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XML Schema Part 2: Datatypes &WD-XSP2;-&iso.doc.date; W3C Working Draft ⅆ&MM;&year;

(in XML and HTML, with a schema and DTD for datatype definitions, as well as a schema for built-in datatypes only.)

&XSP2.base;/ http://www.w3.org/TR/1999/WD-xmlschema-2-19991217/ http://www.w3.org/TR/1999/WD-xmlschema-2-19991105/ http://www.w3.org/TR/1999/WD-xmlschema-2-19990924/ http://www.w3.org/1999/05/06-xmlschema-2/ http://www.w3.org/TR/xmlschema-2/ Paul V. Biron Kaiser Permanente, for Health Level Seven Paul.V.Biron@kp.org Ashok Malhotra IBM petsa@us.ibm.com

This is a public working draft of XML Schema 1.0 for review by the public and by members of the World Wide Web Consortium.

It has been reviewed by the XML Schema Working Group, and the Working Group has agreed to its publication. The WG believes this draft to be `feature-complete': the functionality included here is substantially complete and is expected to be stable. We do not expect to add major new functionality, or to make major changes to the functionality described in this draft. Some sections of the draft (in particular those on conformance), and some aspects of the design (in particular details of the transfer syntax for schemas), on the other hand, are still rough and are expected to be revised.

Following a period of review and polishing, it is the WG's intent to issue a Last Call for Review by other W3C working groups sometime during March, 2000, and to submit this specification thereafter for publication as a Candidate Recommendation. This schedule may vary, depending on the comments of the public and of other W3C working groups on this draft. Such comments are instrumental in the WG's deliberations, and we encourage readers to review the draft and send comments to www-xml-schema-comments@w3.org (archive).

Although the Working Group does not anticipate further substantial changes to the functionality described here, this is still a working draft, subject to change based on experience and on comment by the public and other W3C working groups. The present version should be implemented only by those interested in providing a check on its design or by those preparing for an implementation of the Candidate Recommendation. The Schema WG will not allow early implementation to constrain its ability to make changes to this specification prior to final release.

A list of current W3C working drafts can be found at http://www.w3.org/TR/. They may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use W3C Working Drafts as reference material or to cite them as other than "work in progress".

Several "note types" are used throughout this draft:

something on which the editors are seeking comment.

something the editors wish to call to the attention of the reader. To be removed prior to the recommendation becoming final.

something the editors wish to call to the attention of the reader. To remain in the final recommendation.

XML Schema: Datatypes is part 2 of a two-part draft of the specification for the XML Schema definition language. This document proposes facilities for defining datatypes to be used in XML Schemas and other XML specifications. The datatype language, which is itself represented in XML 1.0, provides a superset of the capabilities found in XML 1.0 document type definitions (DTDs) for specifying datatypes on elements and attributes.

English 2000-02-08: pvb: spell check 2000-02-08: pvb: added COS's for interaction between min/max-X facets 2000-02-08: pvb: changed datatype of length, min/maxlength facets from positive-integer to non-negative-integer 2000-02-08: pvb: corrected typo in date-lexical-representaion, where a "specific century" was noted as YY (changed to CC) 2000-02-08: pvb: changed defn of atomic from being "intrinsically indivisible" to "regarded as indivisible by this specification" 2000-02-08: pvb: clarified defn of facet, wrt value spaces and not "concepts or objects" 2000-02-08: pvb: merged "terminology" sections from both part 1 and part 2 2000-02-08: pvb: fixed datatype of scale facet (from pos-int to non-neg-int) 2000-02-08: pvb: added "priority feedback note" for bigNums 2000-02-09: pvb: fixed circular defn of decimal, as suggested by DC 2000-02-09: pvb: added 1 and 0 to lexical space of boolean 2000-02-09: pvb: added subsections to section 4...this may get undone when I dump the abstract syntax, we'll see 2000-02-10: pvb: added pattern facet to all datatypes 2000-02-10: pvb: updated several incorrect values in the constraining facets "table" in Appendix C2. 2000-02-10: pvb: changed examples to use <documentation> instead of <info> as the child of <annotation> 2000-02-10: pvb: added the correct built-in datatypes namespace to section 3.1 (closes the datatypes portion of issue 78) 2000-02-10: pvb: changed examples to use <simpleType> instead of <datatype>, equivalent changes to the DTD and schema will come shortly closes the datatypes portion of issue 157) 2000-02-10: pvb: renamed uri datatype to uri-reference; clarified the defn wrt RFC 2396; included specific mention of absolute vs. relative uri-references; still need to be specific about the lexical representation (closes some parts of issue 212) 2000-02-15: pvb: added SVC to binary, which says one must give a value for the encoding facet (i.e., a hack to get around the problem that we don't have the concept of "required" facets) [part of the resolution to issue 81] 2000-02-15: pvb: moved ID to a primitive type (since it has validation requirements above and beyond those provided for subtypes of string). Also added a Note: to it making explicit the fact that the value space is scoped to an instance document (unlike the value space of types such as integer). Also fixed a bug in the definition, which refered to Name instead of NCName [part of the resolution to issue 81] 2000-02-15: pvb: moved IDREF to a primitive type (since it has validation requirements above and beyond those provided for subtypes of string). Added an issue about whether this could be generated from ID. Also added a Note: to it making explicit the fact that the value space is scoped to an instance document (unlike the value space of types such as integer). [part of the resolution to issue 81] 2000-02-15: pvb: moved IDREFS to a primitive type (since it has validation requirements above and beyond those provided for subtypes of string)....this is just a temporary home and it will become generated as list of IDREF when I get the list stuff implemented [part of the resolution to issue 81] 2000-02-15: pvb: moved ENTITY to a primitive type (since it has validation requirements above and beyond those provided for subtypes of string). Also added a Note: to it making explicit the fact that the value space is scoped to an instance document (unlike the value space of types such as integer). Also added a SVC that entity values must match a declared unparsed entity name. [part of the resolution to issue 81] 2000-02-15: pvb: moved ENTITIES to a primitive type (since it has validation requirements above and beyond those provided for subtypes of string)....this is just a temporary home and it will become generated as list of ENTITY when I get the list stuff implemented [part of the resolution to issue 81] 2000-02-15: pvb: moved NOTATION to a primitive type (since it has validation requirements above and beyond those provided for subtypes of string). Also added a Note: to it making explicit the fact that the value space is scoped to an instance document (unlike the value space of types such as integer). Also added a SVC that notation values must match a declared notation name. [part of the resolution to issue 81] 2000-02-15: pvb: updated table in appendix C1, to note that all datatypes are exact 2000-02-16: pvb: added i4, i8, u4, u8, etc. subtypes of integer, using editor's discretion in their naming as instructed at the berkeley f2f...changed the first example in section 4 "Defining Generated Datatypes" to use the Sku datatype from Part 0, instead of i4 since we now have i4 built-in 2000-02-16: pvb: removed issue: definition-overriding from the draft 2000-02-17: pvb: removed the exact vs. approximate distinction entirely (since all our types turned out to be exact) 2000-02-17: pvb: removed all mention of aggregate datatypes. Changed the "atomic vs. aggregate" dichotomy to be: atomic vs. list. [part of resolution to issue 112] 2000-02-17: pvb: clarified defns of value space and lexical space. In particular, moved the notion of a literal denoting a value from the defn to LS to VS and noted that a literal is a character information item from the info set. 2000-02-17: pvb: changed terminology of "generated" to "derived", to be in alignment with the structures spec [part of resolution to issue 204] 2000-02-17: pvb: removed definition of term subtype, changed all prose of the form "for subtypes of X" to "for datatypes derived from X" [part of resolution to issue 204] 2000-02-17: pvb: removed a para from Conformance section which mentioned processor option of turning off validation of certain facets 2000-02-17: pvb: removed note that order-relations are not defined 2000-02-17: pvb: made IDREFS, ENTITIES and NMTOKENS derived by list from IDREF, ENTITY and NMTOKENS respectively. [part of resolution of issue 81] 2000-02-17: pvb: clarified what the values {hex,base64} mean for the encoding facet 2000-02-17: pvb: added pointers from the 4 mechanisms to create a value space to the places in the spec where those mechanisms are described 2000-02-17: pvb: all built-in generated types are now defined in the schema for datatypes 2000-02-21: pvb: clarified list datatypes, wrt use of component type which allows whitespace in its literals and wrt facets applicable for deriving subtypes of a list type 2000-02-23: pvb: change defn of binary and meaning of length facet for binary to be measured in octets, since both lexical encodings are only defined for octet multiples. 2000-02-23: pvb: incorporated prose description of regex language (thanx to Matt Timmermans!!!!) 2000-02-23: pvb: added appinfo's to builtin definitions in the schema for datatypes, which are used to generate the list of constraining facets for each builtin datatype in the html version of the spec 2000-02-23: pvb: replaced abstract syntax with 2 new sections for "schema components" and "xml representation" constructs, still needs a lot of editorial work tho 2000-02-23: pvb: list of derived types for each built-in type is now auto-generated from the builtins.xsd 2000-02-23: pvb: appendix C.2 (list of datatypes to which each facet applies) is now auto-generated form the builtins.xsd 2000-02-24: pvb: put equality back in as a fundamental facet, to help with the vote on today's telcon regarding key, unique and keyref value matching. 2000-02-24: pvb: added 'datatype valid' validation constraint 2000-02-24: pvb: added stub for 'facet valid' validation constraint
Introduction Purpose

The specification defines limited facilities for applying datatypes to document content in that documents may contain or refer to DTDs that assign types to elements and attributes. However, document authors, including authors of traditional documents and those transporting data in XML, often require a higher degree of type checking to ensure robustness in document understanding and data interchange.

The table below offers two typical examples of XML instances in which datatypes are implicit: the instance on the left represents a billing invoice, the instance on the right a memo or perhaps an email message in XML.

Data oriented Document oriented
1999-01-21 1999-01-25 Ashok Malhotra 123 IBM Ave. Hawthorne NY 10532-0000 555-1234 555-4321 ]]> Paul V. Biron Ashok Malhotra Latest draft We need to discuss the latest draft immediately. Either email me at mailto:paul.v.biron@kp.org or call 555-9876 ]]>

The invoice contains several dates and telephone numbers, the postal abbreviation for a state (which comes from an enumerated list of sanctioned values), and a ZIP code (which takes a definable regular form). The memo contains many of the same types of information: a date, telephone number, email address and an "importance" value (from an enumerated list, such as "low", "medium" or "high"). Applications which process invoices and memos need to raise exceptions if something that was supposed to be a date or telephone number does not conform to the rules for valid dates or telephone numbers.

In both cases, validity constraints exist on the content of the instances that are not expressible in XML DTDs. The limited datatyping facilities in XML have prevented validating XML processors from supplying the rigorous type checking required in these situations. The result has been that individual applications writers have had to implement type checking in an ad hoc manner. This specification addresses the need of both document authors and applications writers for a robust, extensible datatype system for XML which could be incorporated into XML processors. As discussed below, these datatypes could be used in other XML-related standards as well.

Requirements

The document spells out concrete requirements to be fulfilled by this specification, which state that the XML Schema Language must:

provide for primitive data typing, including byte, date, integer, sequence, SQL & Java primitive data types, etc.;

define a type system that is adequate for import/export from database systems (e.g., relational, object, OLAP);

distinguish requirements relating to lexical data representation vs. those governing an underlying information set;

allow creation of user-defined datatypes, such as datatypes that are derived from existing datatypes and which may constrain certain of its properties (e.g., range, precision, length, format).

Scope

This portion of the XML Schema Language discusses datatypes that can be used in an XML Schema. These datatypes can be specified for element content that would be specified as #PCDATA and attribute values of various types in a DTD. It is the intension of this specification that it be usable outside of the context of XML Schemas for a wide range of other XML-related activities such as and .

Terminology

The terminology used to describe XML Schema Datatypes is defined in the body of this specification. The terms defined in the following list are used in building those definitions and in describing the actions of a datatype processor:

The list below represents a merger of the equivlant sections from both structures and datatypes. Do we really need all of these terms defined in the datatypes spec?

A feature of this specification included solely to ensure that schemas which use this feature remain compatible with

Conforming documents and processors are permitted to but need not behave as described.

(Of strings or names:) Two strings or names being compared must be character for character the same.

(Of URIs) identical, according to the rules for identity in .

Conforming documents and processors are required to behave as described; otherwise they are in error.

A violation of the rules of this specification; results are undefined. Conforming software may detect and report an error and may recover from it.

An error which a conforming processor must detect and report to the application.

Type System

This section describes the conceptual framework behind the type system defined in this specification. The framework has been influenced by the standard on language-independent datatypes as well as the datatypes for and for programming languages such as Java.

The datatypes discussed in this specification are computer representations of well known abstract concepts such as integer and date. It is not the place of this specification to define these abstract concepts; many other publications provide excellent definitions.

Datatype

In this specification, a datatype is defined as a 3-tuple, consisting of a) a set of distinct values, called its , b) a set of lexical representations, called its , and c) a set of facets that characterize properties of the , individual values or lexical items.

Value space

A value space is the set of values for a given datatype. Each value in the value space of a datatype is denoted by one or more literals in its .

The of a given datatype can be defined in one of the following ways:

defined axiomatically from fundamental notions (intensional definition) [see ]

enumerated outright (extensional definition) [see ]

defined by restricting the of an already defined datatype to a particular subset with a given set of properties [see ]

defined as a combination of values from an already defined (s) by a specific construction procedure [see ]

s have certain properties. For example, they always have the property of , some definition of equality and may be by which individual values within the can be compared to one another. The properties of s that are recognized by this specification are defined in .

Lexical space

In addition to its , each datatype also has a lexical space.

A lexical space is the set of valid literals for a datatype (literals may appear as one or more character information items as defined in ).

For example, "100" and "1.0E2" are two different literals from the of which both denote the same value. The type system defined in this specification provides a mechanism for schema designers to control the set of values and the corresponding set of acceptable literals of those values for a datatype.

Facets

A facet is a single defining aspect of a . Generally speaking, each facet characterizes a along independent axes or dimensions.

The facets of a datatype serve to distinguish those aspects of one datatype which differ from other datatypes. Rather than being defined solely in terms of a prose description the datatypes in this specification are defined in terms of the synthesis of facet values which together determine the and properties of the datatype.

Facets are of two types: fundamental facets that define the datatype and non-fundamental or constraining facets that constrain the permitted values of a datatype.

Fundamental facets

A datatype is characterized by properties of its . Each of these properties give rise to a facet that serves to characterize the datatype. These properties are discussed in this section.

Equal

Every supports the notion of equality, with the following rules:

for any two instances of values from the (a,b), either a is equal to b, denoted a = b, or a is not equal to b, denoted a != b;

there is no pair of instances (a, b) of values from the such that both a = b and a != b;

for every value a from the , a = a;

for any two instances (a, b) of values from the , a = b if and only if b = a;

for any three instances (a, b, c) of values from the , if a = b and b = c, then a = c.

On every datatype, the operation Equal is defined in terms of the equality property of the : for any values a, b drawn from the , Equal(a,b) is true if a = b, and false otherwise.

Order

A , and hence a datatype, is said to be ordered if there exists an order relation defined for that .

order relations have the following rules:

for every pair (a, b) from the , either a < b or b < a, or a = b;

for every triple (a, b, c) from the , if a < b and b < c, then a < c.

There may exist several possible order relations for a given . Additionally, there may exist multiple datatypes with the same . In such cases, each datatype will define a different order relation on the .

Bounds

A is bounded above if there exists a unique value U in the such that, for all values v in the , v <= U. The value U is said to be an upper bound of the .

A is bounded below if there exists a unique value L in the space such that, for all values v in the , L <= v. The value L is then said to be a lower bound of the .

A datatype is bounded if its has both an and a .

Cardinality

Every has associated with it the concept of cardinality. Some s are finite, some are countably infinite while still others are uncountably infinite. A datatype is said to have the cardinality of its .

It is sometimes useful to categorize s (and hence, datatypes) as to their cardinality, there are three significant cases:

s that are finite

s that are countably infinite

Numeric

A datatype is said to be numeric if its values are conceptually quantities (in some mathematical number system). A datatype whose values are not is said to be non-numeric .

Constraining or Non-fundamental facets

A Constraining facet is an optional property that can be applied to a datatype to constrain its .

Constraining the consequently constrains the . Adding s to a is described in .

In this section we define all s that are available for use when defining datatypes.

length

length is the number of units of length, where units of length varies depending on the . The value of length must be a .

For datatypes from , length is measured in units of characters. For datatypes from , length is measured in octets (8 bits). For datatypes by , length is measured in list items.

minlength

minlength is the minimum number of units of length, where units of length varies depending on the . The value of minlength must be a .

For datatypes from , minlength is measured in units of characters. For datatypes from , minlength is measured in bits.

length and minlength

It is an for both and to be specified for the same datatype.

minlength <= maxlength

It is an for the value specified for to be greater than the value specified for for the same datatype.

maxlength

maxlength is the maximum number of units of length, where units of length varies depending on the . The value of maxlength must be a .

For datatypes from , maxlength is measured in units of characters. For datatypes from , maxlength is measured in bits.

length and maxlength

It is an for both and to be specified for the same datatype.

pattern

pattern is a constraint on the of a datatype which is achieved by constraining the . The value of pattern must be a .

enumeration

enumeration constrains the to a specified set of values.

No order or any other relationship is implied between the individual items of the enumeration set.

maxInclusive

maxInclusive is the of the for a datatype with the property. The value is inclusive in the sense that the value is itself included in the . The value of maxInclusive must be of the same type as the .

minInclusive <= maxInclusive

It is an for the value specified for to be greater than the value specified for for the same datatype.

maxExclusive

maxExclusive is the of the for a datatype with the property. The value is exclusive in the sense that the value is itself excluded from the . The value of maxExclusive must be of the same type as the .

maxInclusive and maxExclusive

It is an for both and to be specified for the same datatype.

minExclusive <= maxExclusive

It is an for the value specified for to be greater than the value specified for for the same datatype.

minInclusive

minInclusive is the of the for a datatype with the property. The value is inclusive in the sense that the value is itself included in the . The value of minInclusive must be of the same type as the .

minExclusive

minExclusive is the of the for a datatype with the property. The value is exclusive in the sense that the value is itself excluded from the for the datatype. The value of minExclusive must be of the same type as the .

minInclusive and minExclusive

It is an for both and to be specified for the same datatype.

precision

precision is the total number of decimal digits in values of datatypes from . The value of precision must be a .

scale

scale is the total number of decimal digits to the right of the decimal indicator in values of datatypes from . The value of scale must be a . scale less than or equal to precision

It is an for to be greater than .

encoding

encoding is the encoded form of the of datatypes from . The value of encoding must be one of {hex, base64}.

If the value of encoding is hex then each binary octect is encoded as a character tuple, consisting the two hexadecimal digits ([0-9a-fA-F]) representing the octet code. For example, "20" is the hex encoding for the US-ASCII space character.

If the value of encoding is base64 then the entire binary stream is encoding using the Base64 Content-Transfer-Encoding defined in Section 6.8 .

period

period is the frequency of recurrence for values of datatypes from . The value of period must be .

Datatype dichotomies

It is useful to categorize the datatypes defined in this specification along various dimensions, forming a set of characterization dichotomies.

Atomic vs. list datatypes

The first distinction to be made is that between and datatypes.

Atomic datatypes are those having values which are regarded by this specification as being indivisible.

List datatypes are those having values which consist of a sequence of values of an datatype.

For example, a single token which es Nmtoken from could be the value of an datatype (); while a sequence of such tokens could be the value of a datatype ().

Atomic datatypes

datatypes may be either or . The of an datatype is a set of "atomic" values, which for the purposes of this specification, are not further decomposable. The of an datatype is a set of literals whose internal structure is specific to the datatype is question.

List datatypes

datatypes are always . The of a datatype is a set of finite sequences of values. The of a datatype is a set of literals whose internal structure is a whitespace separated sequence of literals of the datatype of the items in the (where whitespace matches S in ).

It is not an to define a datatype from an datatype whose allows whitespace.

<simpleType name='listOfString' base='string' derivedBy='list'/> <someElement xsi:type='listOfString'> this is not list item 1 this is not list item 2 this is not list item 3 </someElement>

In the above example, the value of the someElement element is not a of 3; rather, it is a of 18.

When a datatype is from a datatype, the following s may be used:

For each of the above s, the unit of length is measured in list items.

A datatype which is in this specification need not be an "atomic" datatype in any programming language used to implement this specification. Likewise,a datatype which is a in this specification need not be a "list" datatype in any programming language used to implement this specification.

Primitive vs. derived datatypes

Next, we distinquish between and datatypes.

Primitive datatypes are those that are not defined in terms of other datatypes; they exist ab initio.

Derived datatypes are those that are defined in terms of other datatypes.

For example, a is a well defined mathematical concept that cannot be defined in terms of other datatypes while a is a special case of the more general datatype .

The datatypes defined by this specification fall into both the and categories. It is felt that a judiciously chosen set of datatypes will serve the widest possible audience by providing a set of convenient datatypes that can be used as is, as well as providing a rich enough base from which the variety of datatypes needed by schema designers can be .

Every datatype is defined in terms of an existing datatype, referred to as the base type. base types may be either or .

In the example above, is from the .

A datatype which is in this specification need not be a "primitive" datatype in any programming language used to implement this specification. Likewise, a datatype which is in this specification need not be a "derived" datatype in any programming language used to implement this specification.

Built-in vs. user-derived datatypes

Built-in datatypes are those which are defined in this specification, and may be either or ;

User-derived datatypes are those datatypes that are defined by individual schema designers by giving values to s.

Conceptually there is no difference between the datatypes included in this specification and the datatypes which will be created by individual schema designers. The datatypes are those which are believed to be so common that if they were not defined in this specification many schema designers would end up "reinventing" them. Furthermore, including these datatypes in this specification serves to demonstrate the mechanics and utility of the datatype generation facilities of this specification.

A datatype which is in this specification need not be a "built-in" datatype in any programming language used to implement this specification. Likewise, a datatype which is in this specification need not be a "user-derived" datatype in any programming language used to implement this specification.

Built-in datatypes Namespace considerations

The datatypes defined by this specification are designed so that systems other than the XML Schema Definition Language may use them. To facilitate such usage the datatypes in this specification have the namespace URI:

http://www.w3.org/1999/XMLSchema/datatypes

This applies to both and datatypes.

Each datatype is also associated with a unique namespace. However, datatypes do not come from the XML Datatype Language namespace; rather, they come from the namespace of the schema in which they are defined (see XML Representation of Schemas in ).

As described in more detail in , each datatype must be defined in terms of another datatype in one of two ways: 1) by assigning s which serve to restrict the of the datatype to a subset of the ; 2) by creating a datatype whose consists of finite-length sequences of values of the .

Primitive datatypes

The datatypes defined by this specification are described below. For each datatype, the and are specified, all s which apply to the datatype are and any datatypes from this the datatype are listed.

datatypes can only be added by revisions to this specification.

string

The string datatype represents character strings in XML. The of string is the set of finite sequences of UCS characters ( and ). A UCS character (or just character, for short) is an atomic unit of communication; it is not further specified except to note that every UCS character has a corresponding UCS code point, which is an integer. The property of string is the character number sequence.

We need to harmonize this definition with the I18N character model. Constraining facets Derived datatypes boolean

boolean has the required to support the mathematical concept of binary-valued logic: {true, false}.

Lexical Representation

An instance of a datatype that is defined as can have the following legal lexical values {true, 1, false, 0}, with '1' being the same as 'true' and '0' being the same as 'false'.

Constraining facets float

float corresponds to the IEEE single-precision 32-bit floating point type . The basic of float consists of the values m × 2^e, where m is an whose absolute value is less than 2^24, and e is an between -149 and 104, inclusive. In addition to the basic described above, the of float also contains the following special values: positive and negative zero, positive negative infinity and not-a-number.

The mapping from a literal in the to a value in the of float follows IEEE round to nearest behavior . For further information on mapping literals to values in the , see .

Lexical representation

float values have a single standard lexical representation consisting of a mantissa followed, optionally, by the character "E" or "e", followed by an exponent. The exponent must be an integer. The mantissa must be a decimal number. The representations for exponent and mantissa must follow the lexical rules for and . If the "E" or "e" and the following exponent are omitted, an exponent value of 0 is assumed.

The special values positive and negative zero, positive and negative infinity and not-a-number have 0, -0, INF, -INF and NaN, respectively.

For example, -1E4, 1267.43233E12, 12.78e-2, 12 and INF are all legal literals for float.

Constraining facets double

The double datatype corresponds to IEEE double-precision 64-bit floating point type . The basic of double consists of the values m × 2^e, where m is an whose absolute value is less than 2^53, and e is an between -1075 and 970, inclusive. In addition to the basic described above, the of double also contains the following special values: positive and negative zero, positive negative infinity and not-a-number.

The mapping from a literal in the to a value in the of double follows IEEE round to nearest behavior . For further information on mapping literals to values in the , see .

Lexical representation

double values have a single standard lexical representation consisting of a mantissa followed, optionally, by the character "E" or "e", followed by an exponent. The exponent must be an integer. The mantissa must be a decimal number. The representations for exponent and mantissa must follow the lexical rules for and . If the "E" or "e" and the following exponent are omitted, an exponent value of 0 is assumed.

The special values positive and negative zero, positive and negative infinity and not-a-number have 0, -0, INF, -INF and NaN, respectively.

For example, -1E4, 1267.43233E12, 12.78e-2, 12 and INF are all legal literals for double.

Constraining facets decimal

decimal represents arbitrary precision decimal numbers. The of decimal consists of the values i × 10^n, where i and n are integers, with n being known as the of the .

The use of arbitrary precision decimal numbers (including all datatypes derived from decimal [e.g., ]) in this design impacts the implementation of schema processors in a number of places: checking constraints on s, for example. It may impact interchange between XML schemas and programming languages, databases, etc.

Our design discussions did not reveal convincing evidence of undue burden because of arbitrary precision decimal numbers in this design, but we welcome further input from implementors.

Lexical representation

decimal has a single standard lexical representation. This consists of a finite sequence of decimal digits separated by a period as a decimal indicator, in accordance with the scale and precision facets, with an optional leading sign. If the sign is omitted, "+" is assumed. Leading and trailing zeroes are optional. For example: -1.23, 12678967.543233, +100000.00.

Constraining facets Derived datatypes timeInstant

timeInstant represents a combination of date and time values representing a single instant in time. The of timeInstant is the space of Gregorian dates and legal time values as defined in § 5.4 of .

Lexical Representation

A single lexical representation, which is a subset of the lexical representations allowed by , is allowed for timeInstant. This lexical representation is the extended format CCYY-MM-DDThh:mm:ss.sss where "CC" represents the century, "YY" the year, "MM" the month and "DD" the day, preceded by an optional leading sign to indicate a negative number. If the sign is omitted, "+" is assumed. The letter "T" is the date/time separator and "hh", "mm", "ss.sss" represent hour, minute and second respectively. Additional digits can be used to increase the precision of fractional seconds if desired. To accommodate year values greater than 9999 additional digits can be added to the left of this representation.

This representation can be immediately followed by a "Z" to indicate Coordinated Universal Time. To indicate the time zone, i.e. the difference between the local time and Coordinated Universal Time, the difference immediately follows the time and consists of a sign, + or -, followed by hh:mm. See also .

For example, to indicate 1:20 pm on May the 31st, 1999 for Eastern Standard Time which is 5 hours behind Coordinated Universal Time, one would write: 1999-05-31T13:20:00-05:00.

Constraining facets timeDuration

timeDuration represents a duration of time. The of timeDuration is the space of time durations as defined in § 5.5.3.2 of .

Lexical Representation

A single lexical representation, conforming to a subset of the representations allowed by , is allowed for timeDuration. This lexical representation is the extended format PnYnMnDTnH nMnS, where nY represents the number of years, nM the number of months, nD the number of days, 'T' is the date/time separator, nH the number of hours, nM the number of minutes and nS the number of seconds. The number of seconds can include decimal digits to arbitrary precision. An optional preceding minus sign ('-') is allowed, to indicate a negative duration. If the sign is omitted a positive duration is indicated. See also .

For example, to indicate a duration of 1 year, 2 months, 3 days, 10 hours, and 30 minutes, one would write: P1Y2M3DT10H30M.

Right truncated forms of the above representation are allowed. For example, P1347Y and P1347M are both allowed; P0Y1347M is also allowed. P0Y1347M0D is not allowed and P-1347M is not allowed although -P1347M is allowed.

Time periods, i.e. specific durations of time, can be represented by supplying two items of information: a start instant and a duration or a start instant and an end instant or an end instant and a duration.

Constraining facets recurringInstant

recurringInstant represents an instant of time that recurs with a specific .

Note that we do not attempt to support general recurring instants of time, just those that needed to support and and those that arise from truncated and reduced lexical representations of . See also .

Lexical Representation

The lexical representation for recurringInstant is the left truncated representation for . For example, if the century "CC" is omitted from the timeInstant representation it means a timeInstant that recurs every hundred years. Similarly, if "CCYY" is omitted it designates a time instant that recurs every year.

Every two character "unit" of the representation that is omitted is indicated by a single hyphen "-". For example, to indicate 1:20 pm on May the 31st every year, one would write write: --05-31T13:20:00-05:00.

Constraining facets Derived datatypes binary

binary represents arbitrary binary data. The of binary is the set of finite sequences of binary octets.

encoding required for binary

It is an for binary to be used directly in a schema. Only datatypes that are from binary by specify a value for can be used in a schema.

Constraining facets What does the pattern facet on binary really mean? Since pattern operates on the lexical space, one would have to give a regex for the base64 or hex that would result for a specifc binary sequence that one wanted to constrain...this is not too far fetched for hex, but almost impossible for base64, isn't it? uri-reference

uri-reference represents a Uniform Resource Identifier (URI) Reference as defined in Section 4 of . A uri-reference may be absolute or relative, and may have an optional fragment identifier.

An absolute uri-reference refers to a resource in a manner which is independent of the context in which the occurs.

A relative uri-reference refers to a resource by describing the difference within a hierarchy of resources between the context in which the relative uri-reference occurs and the of the resource.

Lexical representation

to be filled in a future point release

Constraining facets ID

ID represents the ID attribute type from . The of ID is the set of all strings that match the NCName production in and have been used in an XML document. The of ID is the set of all strings that match the NCName production in .

The of ID is scoped to a specifc instance document.

For compatibility (see ) ID should be used only on attributes.

ID Unique

An ID must not appear more than once in an XML document as a value of this type; i.e., ID values must uniquely identify the elements which bear them.

Constraining facets IDREF

IDREF represents the IDREF attribute type from . The of IDREF is the set of all strings that match the NCName production in and have been used in an XML document as the value of an element or attribute of type . The of IDREF is the set of all strings that match the NCName production in .

Can IDREF be defined as a subtype of ID? Since every IDREF must also be an ID I think we're OK...we get around the problem of validation requirements not being supported by our general facet mechanism because of this. However, the only way to do that today would be as follows: <simpleType name='IDREF' basetype='ID'/>, that is, by not giving any facets and, in effect, saying that the value spaces are identical; but, isn't the "real" value space of IDREF a restriction (i.e., a proper subset) of the value space of ID?

The of IDREF is scoped to a specifc instance document.

For compatibility (see ) this datatype should be used only on attributes.

IDREF

An IDREF must match the value of an in the XML document in which it occurs.

Constraining facets Derived datatypes ENTITY

ENTITY represents the ENTITY attribute type from . The of ENTITY is the set of all strings that match the NCName production in and have been declared as an unparsed entity in a DTD. The of ENTITY is the set of all strings that match the NCName production in .

Need a reference to unparsed entity in XML 1.0

The of ENTITY is scoped to a specifc instance document.

ENTITY declared

ENTITY values must match an unparsed entity name that is declared in the schema.

For compatibility (see ) ENTITY should be used only on attributes.

Constraining facets Derived datatypes NOTATION

NOTATION represents the NOTATION attribute type from . The of NOTATION is the set of all notations declared in a schema. The of NOTATION is the set of all strings that match the NCName production in .

The of NOTATION is scoped to a specifc instance document.

NOTATION declared

NOTATION values must match a notation name that is declared in the schema.

For compatibility (see ) NOTATION should be used only on attributes.

Constraining facets Derived datatypes

This section gives conceptual definitions for all datatypes defined by this specification. The XML Representation used to define datatypes (whether or ) is given in section and the complete definitions of the datatypes are provided in Appendix .

language

language represents natural language identifiers as defined by . The of language is the set of all strings that match the LanguageID production in . The of language is the set of all strings that match the LanguageID production in . The of language is .

Constraining facets IDREFS

IDREFS represents the IDREFS attribute type from . The of IDREFS is the set of finite-length sequences of s that have been used in an XML document. The of IDREFS is the set of whitespace separated tokens, each of which is in the of . The of IDREFS is .

The of IDREFS is scoped to a specifc instance document.

For compatibility (see ) IDREFS should be used only on attributes.

Should we include the type definitions for all built-in-derived types inline, such as the following: ]]> Constraining facets ENTITIES

ENTITIES represents the ENTITIES attribute type from . The of ENTITIES is the set of finite-length sequences of s that have been declared as unparsed entities in a DTD. The of ENTITIES is the set of whitespace separated tokens, each of which is in the of . The of ENTITIES is .

The of ENTITIES is scoped to a specifc instance document.

For compatibility (see ) ENTITIES should be used only on attributes.

Constraining facets NMTOKEN

NMTOKEN represents the NMTOKEN attribute type from . The of NMTOKEN is the set of tokens that the Nmtoken production in . The of NMTOKEN is the set of strings that the Nmtoken production in . The of NMTOKEN is .

For compatibility (see ) NMTOKEN should be used only on attributes.

Constraining facets Derived datatypes NMTOKENS

NMTOKENS represents the NMTOKENS attribute type from . The of NMTOKENS is the set of fininte-length sequences of s. The of NMTOKENS is the set of whitespace separated tokens, each of which is in the of . The of NMTOKENS is .

For compatibility (see ) NMTOKENS should be used only on attributes.

Constraining facets Name

Name represents XML Names. The of Name the set of all strings which match the Name production of . The of Name is the set of all strings which match the Name production of . The of Name is .

Constraining facets Derived datatypes QName

QName represents XML qualified names. The of QName is the set of all strings which match the QName production of . The of QName is the set of all strings which match the QName production of . The of QName is .

Constraining facets NCName

NCName represents XML "non-colonized" Names. The of NCName is the set of all strings which match the NCName production of . The of NCName is the set of all strings which match the NCName production of . The of NCName is .

Constraining facets integer

integer is from by fixing the value of to be 0. This results in the standard mathematical concept of the integer numbers. The of integer is the infinite set {...,-2,-1,0,1,2,...} The of integer is .

Lexical representation

integer values have a single, standard lexical representation. This consists of a string of digits with an optional leading sign. If the sign is omitted, "+" is assumed. For example: -1, 0, 12678967543233, +100000.

Constraining facets Derived datatypes non-positive-integer

non-positive-integer is from by fixing the value of to be 0. This results in the standard mathematical concept of the non-positive integers. The of non-positive-integer is the infinite set {...,-2,-1,0}. The of non-positive-integer is .

Lexical representation

non-positive-integer values have a single, standard lexical representation. This consists of a string of digits with a leading "-" sign. For example: -1, 0, -12678967543233, -100000.

Constraining facets Derived datatypes negative-integer

negative-integer is from by fixing the value of to be -1. This results in the standard mathematical concept of the negative integers. The of negative-integer is the infinite set {...,-2,-1}. The of negative-integer is .

Lexical representation

negative-integer values have a single, standard lexical representation. This consists of a string of digits with a leading "-" sign. For example: -1, -12678967543233, -100000.

Constraining facets &long;

&long; is from by fixing the values of to be 9223372036854775807 and to be -9223372036854775808. The of &long; is .

Lexical representation

&long; values have a single, standard lexical representation. This consists of a string of digits with an optional leading sign. If the sign is omitted, "+" is assumed. For example: -1, 0, 12678967543233, +100000.

Constraining facets Derived datatypes ∫

∫ is from by fixing the values of to be 2147483647 and to be -2147483648. The of ∫ is .

Lexical representation

∫ values have a single, standard lexical representation. This consists of a string of digits with an optional leading sign. If the sign is omitted, "+" is assumed. For example: -1, 0, 126789675, +100000.

Constraining facets Derived datatypes &short;

&short; is from by fixing the values of to be 32767 and to be -32768. The of &short; is .

Lexical representation

&short; values have a single, standard lexical representation. This consists of a string of digits with an optional leading sign. If the sign is omitted, "+" is assumed. For example: -1, 0, 12678, +10000.

Constraining facets Derived datatypes &byte;

&byte; is from by fixing the values of to be 127 and to be -128. The of &byte; is .

Lexical representation

&byte; values have a single, standard lexical representation. This consists of a string of digits with an optional leading sign. If the sign is omitted, "+" is assumed. For example: -1, 0, 126, +100.

Constraining facets non-negative-integer

non-negative-integer is from by fixing the value of to be 0. This results in is the standard mathematical concept of the non-negative integers. The of non-negative-integer is the infinite set {0,1,2,...}. The of non-negative-integer is .

Lexical representation

non-negative-integer values have a single, standard lexical representation. This consists of a string of digits with an optional leading "+" sign. If the sign is omitted, "+" is assumed. For example: 1, 0, 12678967543233, +100000.

Constraining facets Derived datatypes &unsigned-long;

&unsigned-long; is from by fixing the values of to be 18446744073709551615. The of &unsigned-long; is .

Lexical representation

&unsigned-long; values have a single, standard lexical representation. This consists of a string of digits with an optional leading sign. If the sign is omitted, "+" is assumed. For example: 0, 12678967543233, +100000.

Constraining facets Derived datatypes &unsigned-int;

&unsigned-int; is from by fixing the values of to be 4294967295. The of &unsigned-int; is .

Lexical representation

&unsigned-int; values have a single, standard lexical representation. This consists of a string of digits with an optional leading sign. If the sign is omitted, "+" is assumed. For example: 0, 1267896754, +100000.

Constraining facets Derived datatypes &unsigned-short;

&unsigned-short; is from by fixing the value to be 65535. The of &unsigned-short; is .

Lexical representation

&unsigned-short; values have a single, standard lexical representation. This consists of a string of digits with an optional leading sign. If the sign is omitted, "+" is assumed. For example: 0, 12678, +10000.

Constraining facets Derived datatypes &unsigned-byte;

&unsigned-byte; is from by fixing the value to be 255. The of &unsigned-byte; is .

Lexical representation

&unsigned-byte; values have a single, standard lexical representation. This consists of a string of digits with an optional leading sign. If the sign is omitted, "+" is assumed. For example: 0, 126, +100.

Constraining facets positive-integer

positive-integer is from by fixing the value of to be 1. This results in the standard mathematical concept of the positive integer numbers. is the standard mathematical concept of the positive integers. The of positive-integer is the infinite set {1,2,...}. The of positive-integer is .

Lexical representation

positive-integer values have a single, standard lexical representation. This consists of a string of digits with an optional leading "+" sign. For example: 1, 12678967543233, +100000.

Constraining facets date

date represents a that starts at midnight of a specified day and lasts for 24 hours. The of date is the set of Gregorian calendar dates as defined in § 5.2.1 of . The of date is .

Lexical Representation

The lexical representation for date is the reduced (right truncated) lexical representation for : CCYY-MM-DD. To accommodate year values greater than 9999 additional digits can be added to the left of this representation. For example, to indicate May the 31st, 1999, one would write: 1999-05-31. See also .

Left truncated representations can be used to represent recurring dates. If the CC is omitted it signifies a date that occurs every century. If the YY is also omitted it signifies a date every year and so on. Every two character "unit" of the representation that is omitted is indicated by a single hyphen "-". For example, ---05 signifies the fifth day of every month.

Right truncated, or reduced precision, date representations can be used to represent a specific month (CCYY-MM), a specific year (CCYY), or a specific century (CC).

Constraining facets time

time represents a recurring instant of time that recurs every day. The of time is the space of time of day values as defined in § 5.3 of . The of time is .

time can be considered to be a shorthand to designate a specific truncated representation for .

Lexical Representation

The lexical representation for time is the left truncated lexical representation for : hh:mm:ss.sss. For example, to indicate 1:20 pm for Eastern Standard Time which is 5 hours behind Coordinated Universal Time, one would write: 13:20:00-05:00. See also .

Constraining facets Datatype components

The following sections provide full details on the properties and significance of each kind of schema component involved in datatype definitions.

this section needs some more explanatory material Datatype definition Optional. An NCName as defined by . A datatype definition. A possibly empty set of . One of {atomic, list}. Either null or a namespace URI, as defined in . Optional. An annotation. Unique datatype definitions

The of the datatype being defined must be unique among the datatypes defined in the containing schema.

Datatype Valid

A sequence of character information items is schema-valid with respect to a datatype definition if:

It is a member of the of the .

The member of the of the denoted by the string is schema-valid with respect to the conditions expressed by all as per .

Datatypes are identified by their and . Except for anonymous datatypes (those with no ), datatype definitions must be uniquely identified within an schema.

Constraining facets

This section provides the details of each component.

Facet valid

A member of a is schema-valid with respect to a component if:

to be specified in detail in the next draft

including mention of a validation constraint for each individual facet below

 length A . Optional. An annotation.

For datatypes from , is in characters. For datatypes from , is in bits. For datatypes by , is in list items.

minlength A . Optional. An annotation.

For datatypes from , is in characters. For datatypes from , is in bits. For datatypes by , is in list items.

maxlength A . Optional. An annotation.

For datatypes from , is in characters. For datatypes from , is in bits. For datatypes by , is in list items.

pattern A . Optional. An annotation. enumeration A value from the of the . Optional. An annotation. maxInclusive A value from the of the . Optional. An annotation. maxExclusive A value from the of the . Optional. An annotation. minExclusive A value from the of the . Optional. An annotation. minInclusive A value from the of the . Optional. An annotation. precision A . Optional. An annotation. scale A . Optional. An annotation. encoding One of {hex, base64}. Optional. An annotation. period A . Optional. An annotation. XML representation of datatype definitions this section needs some more explanatory material Datatype Definitions The value of the name &i-attribute; The value of the base &i-attribute; list ff the value of the derivedBy &i-attribute; (or the derivedBy &i-attribute; of any ancestor) is list; otherwise atomic. The value of the targetNamespace &i-attribute; of the parent schema element information item.

A datatype can be from a datatype or another datatype by one of two means: by restriction or by list.

Derivation by restriction

An electronic commerce schema might define a datatype called Sku (the barcode number that appears on products) from the datatype by supplying a value for the facet.

]]>

In this case, Sku is the name of the new datatype, is its and is the facet.

Derivation by list

blah, blah, blah

]]>

In this case, listOfFloat is the name of the new datatype, is its and is the derivation method.

As mentioned in , when a datatype is from a datatype, the following s may be used:

For each of the above s, the unit of length is measured in list items.

Constraining facets

This section details the XML Representation for specificing s in a datatype definition.

length The value of the value &i-attribute;

The following is the definition of a datatype to represent one form of postal codes in the United States, by limiting strings to be exactly 5 characters in length.

]]> this is a bad example, but its the only one I could think of at the time. minlength The value of the value &i-attribute;

The following is the definition of a datatype which requires strings to have at least one character (i.e., the empty string is not in the of this datatype).

]]> maxlength The value of the value &i-attribute;

The following is the definition of a datatype which might be used to accept form input with an upper limit to the number of characters that are acceptable.

]]> pattern must be a valid . The value of the value &i-attribute;

The following is the definition of a datatype which is a better representation of postal codes in the United States, by limiting strings to those which are matched by a specific .

]]> enumeration must be a valid value of the . The value of the value &i-attribute;

The following example is a datatype definition for a datatype which limits the values of dates to the three US holidays enumerated. This datatype definition would appear in a schema authored by an "end-user" and shows how to define a datatype by enumerating the values in its . The enumerated values must be type-valid literals for the .

some US holidays New Year's day 4th of July Christmas ]]> maxInclusive must be a valid value of the . The value of the value &i-attribute;

The following is the definition of a datatype which limits values to integers less than or equal to 100, using .

]]> maxExclusive must be a valid value of the . The value of the value &i-attribute;

The following is the definition of a datatype which limits values to integers less than or equal to 100, using .

]]>

Note that the of this datatype is identical to the previous one (named 'one-hundred-or-less').

minInclusive must be a valid value of the . The value of the value &i-attribute;

The following is the definition of a datatype which limits values to integers greater than or equal to 100, using .

]]> minExclusive must be a valid value of the . The value of the value &i-attribute;

The following is the definition of a datatype which limits values to integers greater than or equal to 100, using .

]]>

Note that the of this datatype is identical to the previous one (named 'one-hundred-or-more').

precision The value of the value &i-attribute;

The following is the definition of a datatype which limits values to integers greater than or equal to 100, using .

]]> scale The value of the value &i-attribute;

The following is the definition of a datatype which could be used to represent monetary amounts, such as in a financial management application which does not have figures above $1M and only allow whole cents. This definition would appear in a schema authored by an "end-user" and shows how to define a datatype by specifying facet values which constrain the range of the in a manner specific to the (different than specifying max/min values as before)

]]> encoding The value of the value &i-attribute;

The following example is a datatype definition for a datatype whose is the set of binary streams of length 4 octets (32 bits) and whose is the set of base64 encodings of such binary streams. This datatype definition would appear in a schema authored by an "end-user" and shows how to define a datatype by specifying multiple s.

]]> period The value of the value &i-attribute; Conformance This section (both its abstract content and its concrete wording) has not yet garnered consensus among WG members.

The XML specification defines two levels of conformance. Well-formed documents conform to valid XML syntax but may or may not obey the constraints defined by a DTD. Valid XML documents conform to the structure laid down in a DTD. Thus, if a DTD defines an attribute as an , instances of XML documents conforming to the DTD can only be valid if the values of such attributes are valid XML names and are unique in the document. By introducing additional datatypes to XML, this specification extends the notion of validity in the sense that values defined to have a certain datatype in the schema must conform to the lexical representations allowed for that datatype. Values that do not conform to the datatype defined for them in the schema raise a conformance error. As, for example, the appearance of a letter in a value defined as . Similarly, for a datatype from with equal to 5, a value of "ABC" would raise an error -- length too short -- as would a value of "abcdefgh" -- length too long.

For conformance it is not enough that the representation conform to a legal literal in the of the datatype; it must also represent a legal value in the . For example, the , , , and values must conform to legal Gregorian dates and legal time values as specified in the descriptions of these datatypes.

It also needs to be said that there are no expressions on datatypes; neither are there operations on datatypes.

If we decide to allow datatype specification or specialization in instance documents (see issue "definition-overriding" above) then validating XML processors should be able to validate the format of values in XML documents in these cases as well by using the datatypes processor.

Schema for Datatype Definitions (normative) DTD for Datatype Definitions (normative) Datatypes and Facets Fundamental Facets

The following table shows the values of the fundamental facets for each datatype.

  Datatype
yes none countably infinite no
no none finite no
yes yes finite yes
yes yes finite yes
yes no countably infinite yes
yes no countably infinite no
yes no countably infinite no
yes no countably infinite no
no no countable infinite no
no no countably infinite no
no no countably infinite no
no no countably infinite no
no no countably infinite no
no no countably infinite no
no no countably infinite no
no no countably infinite no
no no countably infinite no
no none countably infinite no
no no countably infinite no
no no countably infinite no
no no countably infinite no
no no countably infinite no
yes no countably infinite yes
yes yes countably infinite yes
yes yes countably infinite yes
yes yes finite yes
yes yes finite yes
yes yes finite yes
yes yes finite yes
yes yes countably infinite yes
yes yes finite yes
yes yes finite yes
yes yes finite yes
yes yes finite yes
yes yes countably infinite yes
yes no countably infinite no
yes no countably infinite no
Constraining Facets

The s are listed below with all the and datatypes that they apply to.

ISO 8601 Date and Time Formats ISO 8601 Conventions

Three datatypes described above, , , and , and two dataypes, and use lexical formats inspired by . This appendix provides more detail on the ISO formats and discusses some deviations from them for the datatypes we have defined.

"specifies the representation of dates in the Gregorian calendar and times and representations of periods of time". It should be pointed out that the datatypes described in this specification do not cover all the types of data covered by , nor do they support all the lexical representations for those types of data. Specifically, we permit only a single lexical representation for each datatype.

lexical formats are described using "pictures" in which characters are used in place of digits. These characters have the following meanings:

C -- represents a digit used in the thousands and hundreds components, the "century" component, of the time element "year".

Y -- represents a digit used in the tens and units components of the time element "year".

M -- represents a digit used in the time element "month".

D -- represents a digit used in the time element "day".

h -- represents a digit used in the time element "hour".

m -- represents a digit used in the time element "minute".

s -- represents a digit used in the time element "second". In the formats described in this specification the whole number of seconds may be followed by decimal seconds to an arbitrary level of precision. This is represented in the picture by "ss.sss"

For all the information items indicated by the above characters, leading zeros are required where indicated.

In addition to the above, certain characters are used as designators and appear as themselves in lexical formats.

T -- is used as time designator to indicate the start of the representation of the time of day in and . It is also used to to indicate the start of the representation of the time-units for hour, minutes, seconds and fractional seconds in .

Z -- is used as time-zone designator, immediately (without a space) following a data element expressing the time of day in Coordinated Universal Time (UTC) in , , and

Truncated Formats

supports a variety of "truncated" formats in which some of the characters on the left of specific formats, such as, for example, the century, can be omitted. Truncated formats are, in general, not permitted for the datatypes defined in this specification with two exceptions. The datatype uses a truncated format for to indicate recurring instants of time. In fact, only recurring instants that can be represented truncated representations of are permitted.

Left truncated representations are also allowed for the datatype and can be used to represent recurring dates i.e. the same date every century, every year or every month. Right truncated, or reduced precision, representations are also allowed for and can be used to represent a specific month, a specific year, or a specific century.

 Deviations from ISO 8601 Formats Sign Allowed

An optional minus sign is allowed immediately preceding, without a space, the lexical representations for and .

More Than 9999 Years

To accommodate year values greater than 9999, more than four digits are allowed in the year representations of , and . This follows the .

Regular Expressions

A regular expression R is a sequence of characters that denotes a set of strings L(R). When used to constrain the lexical space of a datatype, a regular expression R asserts that only strings in L(R) are valid specifications for values of that type.

A regular expression is composed from one or more es, separated by | characters.

For all es S, and for all s T, valid s R are: Denoting the set of strings L(R) containing:
S all strings in L(S)
S|T all strings in L(S) and all strings in L(T)

A branch consists of zero or more s, concatenated together.

For all s S, and for all es T, valid es R are: Denoting the set of strings L(R) containing:
S all strings in L(S)
ST all strings st with s in L(S) and t in L(T)

A piece is an , possibly followed by a .

For all s S, valid s R are: Denoting the set of strings L(R) containing:
S all strings in L(S)
S? the empty string, and all strings in L(S).
S* All strings st with s in L(S?) and t in L(S*). ( all concatenations of zero or more strings from L(S) )
S+ All strings st with s in L(S) and t in L(S*). ( all concatenations of one or more strings from L(S) )

An atom is either a , a , or a parenthesized .

For all s c, es C, and s S, valid s R are: Denoting the set of strings L(R) containing:
c the single string consisting only of c
C all strings in L(C)
(S) all strings in L(S)

A quantifier is is either ?, *, or +.

A metacharacter is either ., \, ?, *, +, (, ), [, or ]. These characters have special meanings in s, but can be escaped to form s that denote the sets of strings containing only themselves, i.e., an escaped behaves like a .

A normal character is any XML character that is not a metacharacter. In s, a normal character is an atom that denotes the singleton set of strings containing only itself.

Character Classes

A character class is an R that identifies a set of characters C(R). The set of strings L(R) denoted by a character class R contains one single-character string "c" for each character c in C(R).

A character class is either a or a .

A character class expression is a surrounded by [ and ] characters. For all character groups G, [G] is a valid character class expression, identifying the set of characters C([G]) = C(G).

A character group is either , a , or a .

A positive character group consists of one or more s or s, concatenated together. A positive character group identifies the set of characters containing all of the characters in all of the sets identified by its constituent ranges or escapes.

For all s R, all s E, and all s P, valid s G are: Identifying the set of characters C(G) containing:
R all characters in C(R).
E all characters in C(E).
RP all characters in C(R) and all characters in C(P).
EP all characters in C(E) and all characters in C(P).

A negative character group is a preceded by the ^ character. For all s P, ^P is a valid negative character group, and C(^P) contains all XML characters that are not in C(P).

A character class subtraction is a subtracted from a positive or negative character group, using the - character.

For any positive or negative character group G, and any C, G-C is a valid character class subtraction, identifying the set of all characters in C(G) that are not also in C(C).

A character range R identifies a set of characters C(R) containing all XML characters with Unicode code points in a specified range.

A single XML character is a character range that identifies the set of characters containing only itself. All XML chacters are valid character ranges, except as follows:

The [, ], and \ characters are not valid character ranges;

The ^ character is only valid at the beginning of a if it is part of a ; and

The - character is a valid character range only at the beginning or end of a .

A character range may also be written in the form s-e, identifying the set that contains all XML characters with Unicode code points greater than or equal to the code point of s, but not greater than the code point of e.

s-e is a valid character range iff:

s is a , or an XML character;

s is not \

If s is the first character in a , then s is not ^

e is a , or an XML character;

e is not \ or [; and

The code point of e is greater than or equal to the code point of s;

The code point of a is the code point of the single character in the set of characters that it identifies.

 Character Class Escapes

A character class escape is a short sequence of characters that identifies predefined character class. The valid character class escapes include the s, the s, and the s.

A single character escape identifies a set containing a only one character -- usually because that character is difficult or impossible to write directly into a .

The valid single character escapes are: Identifying the set of characters C(R) containing:
\n the newline character (&#xA;)
\r the return character (&#xD;)
\t the tab character (&#x9;)
\\ \
\. .
\- -
\^ ^
\? ?
\* *
\+ +
\( (
\) )
\[ [
\] ]

The Unicode Standard defines a number of character properties and provides mappings from code points to specific character properties. The set containing of all characters that have property X, may be identified with a category escape \p{X}. The compliment of this set may be specified with the category escape \P{X}. ([\P{X}] = [^\p{X}]).

The following table specifies the main character properties (for more information, see Chapter 4 of ).

CategoryPropertyMeaning
LettersLAll Letters
LuUppercase
LlLowercase
LtTitlecase
LmModifier
LoOther
 
MarksMAll Marks
MnNon-Spacing
McSpacing Combining
MeEnclosing
 
NumbersNAll Numbers
NdDecimal Digit
NlLetter
NoOther
 
PunctuationPAll Punctuation
PcConnector
PdDash
PsOpen
PeClose
PiInitial quote (may behave like Ps or Pe depending on usage)
PfFinal quote (may behave like Ps or Pe depending on usage)
PoOther
 
SeparatorsZAll Separators
ZsSpace
ZlLine
ZpParagraph
 
SymbolsSAll Symbols
SmMath
ScCurrency
SkModifier
SoOther
 
OtherCAll Others
CcControl
CfFormat
CsSurrogate
CoPrivate Use
CnNot Assigned

A multi-character escape provides a simple way to identify a commonly used set of characters:

Character Sequence Equivalent
.[^\n\r]
\s[&#x20;\t\n\r]
\S[^\s]
\i[\p{L}\p{Nl}:_]
\I[^\i]
\c[\p{?}\p{?}]
\C[^\c]
\d\p{Nd}
\D[^\d]
\w[\p{?}\p{?}]
\W[^\w]
References Normative IEEE. IEEE Standard for Binary Floating-Point Arithmetic. See http://standards.ieee.org/reading/ieee/std_public/description/busarch/754-1985_desc.html World Wide Web Consortium. XML Information Set (public WD) Available at: http://www.w3.org/TR/xml-infoset World Wide Web Consortium. Extensible Markup Language (XML) 1.0. Available at: &xmlspec; XML Schema Part 1: Structures. Available at: &xsdl; XML Schema Requirements. Available at: http://www.w3.org/TR/NOTE-xml-schema-req ISO (International Organization for Standardization). ISO/IEC 10646-1993 (E). Information technology --- Universal Multiple-Octet Coded Character Set (UCS) --- Part 1: Architecture and Basic Multilingual Plane. [Geneva]: International Organization for Standardization, 1993 (plus amendments AM 1 through AM 7). The Unicode Consortium. The Unicode Standard, Version 2.0. Reading, Mass.: Addison-Wesley Developers Press, 1996. The Unicode Consortium. The Unicode Character Database. Available at: ftp://ftp.unicode.org/Public/3.0-Update/UnicodeCharacterDatabase-3.0.0.html World Wide Web Consortium. Namespaces in XML. Available at: &xmlnsspec; Tim Berners-Lee, et. al. RFC 2396: Uniform Resource Identifiers (URI): Generic Syntax.. 1998 Available at: http://www.ietf.org/rfc/rfc2396.txt N. Freed and N. Borenstein. RFC 2045: Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies. 1996 Available at: http://www.ietf.org/rfc/rfc2045.txt H. Alvestrand, ed. RFC 1766: Tags for the Identification of Languages 1995. Available at: http://www.ietf.org/rfc/rfc1766.txt Non-normative Mark Davis. Unicode Regular Expression Guidelines, 1988. Available at: http://www.unicode.org/unicode/reports/tr18/ The Perl Programming Language. See http://www.perl.com The Perl Programming Language, Version 5.6. See http://www.perl.com/language/misc/ann58/index.html SQL Standard. See http://www.jcc.com/SQLPages/jccs_sql.htm William D Clinger. How to Read Floating Point Numbers Accurately. In Proceedings of Conference on Programming Language Design and Implementation, pages 92-101. Available at: ftp://ftp.ccs.neu.edu/pub/people/will/howtoread.ps ISO (International Organization for Standardization). Representations of dates and times, 1988-06-15. Available at: http://www.iso.ch/markete/8601.pdf ISO (International Organization for Standardization). Representations of dates and times, draft revision, 1998. ISO (International Organization for Standardization). Language-independent Datatypes. See http://www.iso.ch/cate/d19346.html World Wide Web Consortium. RDF Schema Specification. Available at: &rdfschspec; World Wide Web Consortium. Extensible Stylesheet Language (XSL). Available at: &xslspec; Acknowledgments (non-normative)

The following have contributed material to this draft:

Matt Timmermans Mark Reinhold

The editors acknowledge the members of the XML Schema Working Group, the members of other W3C Working Groups, and industry experts in other forums who have contributed directly or indirectly to the process or content of creating this document. The Working Group is particularly grateful to Lotus Development Corp. and IBM for providing teleconferencing facilities.

The current members of the XML Schema Working Group are:

David Beech Oracle Corp. Paul V. Biron Health Level Seven Don Box DevelopMentor Allen Brown Microsoft Greg Bumgardner Rogue Wave Software Lee Buck Extensibility Charles Campbell Informix Peter Chen Bootstrap Alliance and LSU David Cleary Progress Software Dan Connolly W3C staff contact Andrew Eisenberg Progress Software Rob Ellman Calico Commerce David Ezell Hewlett Packard Company David Fallside IBM Matthew Fuchs Commerce One Paul Grosso ArborText, Inc. Dave Hollander CommerceNet co-chair Mary Holstege Calico Commerce Jane Hunter Distributed Systems Technology Centre (DSTC Pty Ltd) Renato Iannella Distributed Systems Technology Centre (DSTC Pty Ltd) Rick Jelliffe Academia Sinica Dianne Kennedy Graphic Communications Association Andrew Layman Microsoft Dmitry Lenkov Hewlett Packard Company Eve Maler Sun Microsystems Ashok Malhotra IBM Murray Maloney Commerce One John McCarthy Lawrence Berkeley National Laboratory Noah Mendelsohn Lotus Development Corporation Don Mullen Extensibility Frank Olken Lawrence Berkeley National Laboratory Dave Peterson Graphic Communications Association Mark Reinhold Sun Microsystems Jonathan Robie Software AG Lew Shannon NCR C. M. Sperberg-McQueen W3C co-chair Henry S. Thompson University of Edinburgh Matt Timmermans Microstar Jim Trezzo Oracle Corp. Steph Tryphonas Microstar Mark Tucker Health Level Seven Asir Vedamuthu webMethods Priscilla Walmsley XMLSolutions Norm Walsh ArborText, Inc. Aki Yoshida SAP AG

The XML Schema Working Group has benefited in its work from the participation and contributions of a number of people not currently members of the Working Group, including in particular those named below. Affiliations given are those current at the time of their work with the WG.

Paula Angerstein Vignette Corporation Gabe Beged-Dov Rogue Wave Software Dean Burson Lotus Development Corporation George Feinberg Object Design Charles Frankston Microsoft Ernesto Guerrieri Inso Michael Hyman Microsoft Setrag Khoshafian Technology Deployment International (TDI) Janet Koenig Sun Microsystems Ara Kullukian Technology Deployment International (TDI) Murata Makoto Xerox Chris Olds Wall Data Shriram Revankar Xerox William Shea Merrill Lynch Ralph Swick W3C Tony Stewart Rivcom Open Issues Revisions from Previous Draft