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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 accompanying schema and DTD)

&XSP2.base;/ 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.

The WG expects to spend January, 2000, working out details, clarifying points of uncertainty that arise in the review of this draft, cleaning up inconsistencies, reviewing the design of the concrete transfer syntax, and making editorial improvements.

Following that 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 February, 2000, and to submit this specification in March, 2000, 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 1999-11-08: PVB: removed real datatype and all references to it 1999-11-08: PVB: added inital definitions for float and double datatypes. This initial definition is not intended to be complete, we need a more complete description of the round-to-nearest behavior of mapping literals into the value space (i.e., a more readable description of "best approximation" from the Clinger paper in the non-normative references section). 1999-11-08: PVB: corrected typos in the definitions of datatypes generated from integer to corrected identify the generated type 1999-11-08: PVB: added specref elements to all mentions of constraining facets 1999-11-08: PVB: added term elements to all mentions of a datatype name in the definition of that datatype 1999-11-12: PVB: changed lexical space of timeDuration to be more consistent with ISO 8601, nYnMnDTnHnMnS (minus the 'P' designator). 1999-11-12: PVB fixed productions for decimalLiteral to allow forms such as -.12 and -23. 19991122: AM: Added some more explanation to timeDuration format. Fixed Appendix D to reflect changes. 19991122: AM: Added "uncountable infinite and exact" value space to 2.4.1.3 19991122: AM: Removed issue "Better Reference Mechanisms". 19991122: AM: Added "collation sequence for strings is Unicode characater number". 19991122: AM: Added min/max facets to date/time dataypes. 19991122: AM: Removed issues on URI and binary datatypes. 19991122: AM: Added value space validation to conformance section. 19991122: AM: Added values space definitions to date/time datatypes. 1999-12-08: pvb: Added QName datatype 1999-12-08: pvb: changed language to be a subtype of string 1999-12-10: pvb: many small editorial changes for consistency 1999-12-10: pvb: Added pattern facet to all date/time types (should have been there all along) 1999-12-10: pvb: Added full list of facets and subtypes to each type definition 1999-12-10: pvb: replaced regex appendix with a brief summary of proposed Unicode support, complete proposal coming shortly 1999-12-10: pvb: moved some references from normative to non-normative 1999-12-10: pvb: changed concrete syntax for datatype defns to more closely match the structures draft: in particular, to allow annotations on the datatype element and all facet elements. 1999-12-15: pvb: added normaitive reference to RTC 2045 for def of base64 1999-12-15: pvb: many more small editorial changes, for consistency in style and presentation 1999-12-15: pvb: corrected small errors in table in appendix C.1, Fundamental facets 1999-12-15: pvb: filled out list of datatypes for each facet in appendix C.2, Constraining facets 1999-12-15: expanded abstract 1999-12-15: pvb: updated description of lexical space for float/double to include literals for +- inf, +- 0, nan. 1999-12-16: pvb: modified defns of ID, IDREF, IDREFS, ENTITY, ENTITIES and NOTATION to match NCName instead of Name as required by the Namespaces in XML spec 1999-12-16: pvb: fully specified value space for decimal
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 a 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 .

For the most part, this specification discusses what are sometimes referred to as datatypes in that they constrain the lexical representation of a single literal. In some cases, as for example in , and , the value may consist of a list or set of literals separated by spaces. This is an example of what is called an datatype. Future versions of this specification may contain a more general mechanism for (collection) datatypes such as sets, bags and records.

The WG has voted to have a simple list aggregate construct. A list will be whitespace separated list of some atomic datatype. There was not time to incorporate that vote into this draft. This vote will affect the , , and types. The list generator will be available to all schema authors. 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:

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

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 permitted values for a given datatype.

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

enumerated outright (extensional definition)

defined axiomatically from fundamental notions (intensional definition)

defined as the subset of values from an already defined with a given set of properties

defined as a combination of values from some already defined (s) by a specific construction procedure

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.

Lexical space

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

A lexical space is a set of valid literals for a datatype. Each value in the datatype's is denoted by one or more literals in its lexical space.

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.

Datatype dichotomies

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

Atomic vs. aggregate datatypes

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

Atomic datatypes are those having values which are intrinsically indivisible.

Aggregate datatypes are those having values which can be decomposed into two or more component values.

For example, a date that is represented as a single character string could be the value of an date datatype; while another date represented as separate "month", "day" and "year" elements would be the value of an date datatype. Not surprisingly, the distinction is analogous to that between an XML element whose content model is #PCDATA and one with element content.

As discussed above, this specification focuses mainly on datatypes. Later versions of this specification may address datatypes in more detail. Note that the legacy XML attribute types , and are conceptually types (lists), although at present they are defined in this specification as .

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

Primitive vs. generated datatypes

Next, we distinquish between and datatypes.

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

Generated 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 generated.

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 "generated" datatype in any programming language used to implement this specification.

Every datatype is defined in terms of an existing datatype, referred to as the basetype. basetypes may be either or .

If type a is the of type b, then b is said to be a subtype of a. The of a subtype is a subset of the of the .

In the example above, is a of the .

Built-in vs. user-generated datatypes

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

User-generated datatypes are those datatypes that are defined by individual schema designers by giving values to facets.

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-generated" datatype in any programming language used to implement this specification.

Facets

A facet is a single defining aspect of a concept or an object. Generally speaking, each facet characterizes a concept or object along independent aspects 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

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

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 .

Currently, no order relations are defined on the datatypes provided by this specification; additionally, there is no means to specify an order relation on datatypes. This will be addressed in a future draft. 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 and exact (see )

s that are countably infinite and approximate (see )

Every finite is necessarily exact. No computational datatype has a that is is uncountably infinite.

Exact and Approximate

The computational representation of a datatype may limit the degree to which values of the datatype can be distinguished.

If every value in the of the conceptual datatype is distinguishable in the computational representation from every other value in the , then the datatype is said to be exact. If a datatype is not exact then it is approximate.

Certain mathematical datatypes with very large or infinite value spaces have representations which are said to be approximate in that multiple values in the conceptual map to single values in the of the representation. In this specification, all approximate datatypes have computational models which specify, via parametric values, a degree of approximation, that is, they require a certain minimum set of values of the mathematical datatype to be distinguishable in the computational datatype. Further, each value in the conceptual must be capable of being represented in the representational within a certain distance i.e. the difference between the conceptual value and the representational value must not exceed some agreed upon value.

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

Constraining facets are optional properties that can be applied to a datatype to constrain its .

Constraining the consequently constrains the . Adding constraining facets to a is used in .

In this section we define all facets that are available for use when generating subtypes.

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 subtypes of , length is measured in units of characters. For subtypes of , length is measured in bits.

We need to ultimately reconcile the notion of string length with the resolution of the i18n issues around character, indexing, etc. I18N recommends that length and maxlength be a "character count" and do not indicate storage requirements. 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 subtypes of , minlength is measured in units of characters. For subtypes of , minlength is measured in bits.

length and minlength

It is an error for both and to be specified 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 subtypes of , maxlength is measured in units of characters. For subtypes of , maxlength is measured in bits.

length and maxlength

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

pattern

For subtypes of , pattern can be used to constrain the allowable values using . For subtypes of the date and time related types (, , , and ), pattern can be used to constrain the allowable values using IS0 8601 "pictures" ().

enumeration

enumeration constrains the of the datatype to the specified list. No order or any other relationship is implied between the elements of the enumeration list.

can be applied to all datatypes exception for the following: and .

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 .

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 error for both and to be specified 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 error for both and to be specified for the same datatype.

precision

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

scale

scale is the total number of decimal digits to the right of the decimal point in values of subtypes of . The value of scale must be a . scale less or equal to precision

It is an error for to be greater than .

encoding

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

period

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

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 come from the XML Datatype Language namespace, the specific namespace defined by this specification. This applies to both and datatypes.

The exact URIs for the namespace(s) defined by this W3C specification is still an open issue. This issue has been raised with the XML Coordination Group (issue 1999-0201-07 Standardizing W3C namespace URIs) for general coordination and resolution. On August 11, Dan Connolly recommended we make up our own URI for datatypes. See http://lists.w3.org/Archives/Member/w3c-xml-schema-ig/1999Aug/0060.html (Member only).

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 Association of components with a target namespace in .

As described in more detail in , each datatype must be defined in terms of another datatype, by assigning facets which serve to constrain the value set of the datatype to a subset of the .

Primitive datatypes

The datatypes defined by this specification are described below. For each datatype, the and are specified, all facets which apply to the datatype are enumerated and , if any, defined by this specification 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 of string

string has the following constraining facets:

Subtypes of string

string has the following subtypes:

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, false}.

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" 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 default lexical rules for and . If the "E" and the the following exponent are omitted, an exponent value of 1 is assumed.

The specical 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 of float

float has the following 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" 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 default lexical rules for integer and decimal numbers discussed above. If the "E" and the the following exponent are omitted, an exponent value of 1 is assumed.

The specical 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 of double

double has the following constraining facets:

decimal

decimal represents arbitrary precision decimal numbers. The of decimal consists of the values i × 10^n, where i is an and n is an .

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 of decimal

decimal has the following constraining facets:

Subtypes of decimal

decimal has the following subtypes:

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 accomodate 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 of timeInstant

timeInstant has the following 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 PnYnMnDTnHnMnnS, where Y represents the number of years, M the number of months, D the number of days, T is the date/time separator, H the number of hours, M the number of minutes and S 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: 1Y2M3DT10H30M.

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 of timeDuration

timeDuration also has the following 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 of recurringInstant

recurringInstant has the following constraining facets:

Subtypes of recurringInstant

recurringInstant has the following subtypes:

binary

binary represents binary data. The of binary is the set of finite sequences of binary bits.

Constraining facets of binary

binary has the following constraining facets:

uri

uri represents a Uniform Resource Identifier (URI) Reference as defined in .

Constraining facets of uri

uri has the following constraining facets:

Generated datatypes

This section gives conceptual definitions for all datatypes defined by this specification. The used to define datatypes (whether or ) is given in section and the complete definitions of the datatypes (written in the based on that abstract syntax given in Appendix ) 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 of language

language has the following constraining facets:

NMTOKEN

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

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

Constraining facets of NMTOKEN

NMTOKEN has the following constraining facets:

Subtypes of NMTOKEN

NMTOKEN has the following subtypes:

NMTOKENS

NMTOKENS represents the NMTOKENS attribute type from . It consists of a whitepsace-separated list of NMTOKENs. The of NMTOKENS is the set of all strings that match the Nmtokens production in . The of ID is the set of all strings that match the Nmtokens production in . The of NMTOKENS is .

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

Constraining facets of NMTOKENS

NMTOKENS has the following constraining facets:

Subtypes of NMTOKENS

NMTOKENS has the following subtypes:

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 of Name

Name has the following constraining facets:

Subtypes of Name

Name has the following subtypes:

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 of QName

QName has the following 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 of NCName

NCName has the following constraining facets:

Subtypes of NCName

NCName has the following subtypes:

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 Name production in . The of ID is .

Constraining facets of ID

ID has the following constraining facets:

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.

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 ID. The of IDREF is the set of all strings that match the NCName production in . The of IDREF is .

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

Constraining facets of IDREF

IDREF has the following constraining facets:

IDREF

each Name must match the value of an in the XML document; i.e. IDREF values must match the value of some .

IDREFS

IDREFS represents the IDREFS attribute type from . It consists of a whitespace-separated list of s. The of IDREFS is the set of all strings that match the Names production in (modified as required by Conformance in ) and have been used in an XML document as the value of an element or attribute of type ID. The of IDREFS is the set of all strings that match the Names production in (modified as required by Conformance in ). The of IDREFS is .

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

Constraining facets of IDREFS

IDREFS has the following constraining facets:

Subtypes of IDREFS

IDREFS has the following subtypes:

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 schema. The of ENTITY is the set of all strings that match the NCName production in . The of ENTITY is .

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

Constraining facets of ENTITY

ENTITY has the following constraining facets:

ENTITIES

ENTITIES represents the ENTITIES attribute type from . It consists of a whitespace-separated list of s. The of ENTITIES is the set of all strings that match the Names production in (modified as required by Conformance in ) and have been declared as an Unparsed Entity in a schema. The of ENTITIES is the set of all strings that match the Names production in (modified as required by Conformance in ). The of ENTITIES is .

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

Constraining facets of ENTITIES

ENTITIES has the following constraining facets:

Subtypes of ENTITIES

ENTITIES has the following subtypes:

NOTATION

NOTATION represents the NOTATION attribute type from and allows the identification of the format of unparsed entities by name. 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 .

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

Constraining facets of NOTATION

NOTATION has the following constraining facets:

integer

integer is 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 of integer

integer has the following constraining facets:

Subtypes of integer

integer has the following subtypes:

non-negative-integer

non-negative-integer 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 of non-negative-integer

non-negative-integer has the following constraining facets:

Subtypes of non-negative-integer

non-negative-integer has the following subtypes:

positive-integer

positive-integer 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 of positive-integer

positive-integer has the following constraining facets:

non-positive-integer

non-positive-integer is 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 of non-positive-integer

non-positive-integer has the following constraining facets:

Subtypes of non-positive-integer

non-positive-integer has the following subtypes:

negative-integer

negative-integer is 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 of negative integer

negative-integer has the following 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 accomodate 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 (YY).

Constraining facets of date

date has the following 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 of time

time has the following constraining facets:

Defining Generated Datatypes

A datatype can be defined from a datatype (or another datatype) by adding optional constraining facets. For example, it may be useful to define a datatype called i4 (signed 4-byte integer) from the datatype by supplying and facets. In this case, i4 is the name of the new datatype, is its and and are the facets.

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This section defines the abstract syntax used for defining datatypes. This abstract syntax is used for defining both and datatypes; the only difference between the and datatypes being that the datatype definitions for datatypes are included in the while the datatype definitions for datatypes appear in schemas written by users.

An abstract syntax provides a formal specification of the information provided for each datatype definition. The abstract syntax is presented using a simplified BNF. Defined terms are to the left. Their components are to the right, with a small amount of meta-syntax: ()s for grouping, | to separate alternatives, ? for optionality, * and + for iteration.

The concrete syntax for datatype definitions is the exact element and attribute names used in definitions.. The concrete syntax is a key feature of its proposed design. The concrete syntax is the form in which the schema language is used by datatype designers. Though its elements and attributes are often different from the terms of the abstract syntax bnf, the features and expressive power of the two are congruent.

We include a preliminary concrete syntax in this draft, via examples, as well as in (defined using the schema language of ) and . The emphasis in this version has been to stay quite close to the abstract syntax.

The abstract syntax proposed here (and hence, the concrete syntax) are preliminary, as they allow datatype definitions which are logically inconsistent (e.g., they allow facets on datatypes). This will be corrected in future drafts, as the XML Schema language comes to allow the specification of tighter constraints. This section needs more explanatory text describing the productions and their relationship to the conceptual framework described in sections and . Datatype definitions datatypeDefn NCName basetype facets basetype datatypename facets ordered? unordered?

The following is the definition for a possible datatype "currency". This datatype definition would appear in the schema which defines datatypes for XML Schemas and shows that a datatype can have the same as its , which might mean that it is just an "alias" or "renaming" of . In this case, the specification would probably also define some "semantics" for currency which went beyond those of decimal.

]]> Unique datatype definitions

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

Appropriate facets

If the of the is , then only facets may appear in a datatype definition.

Datatype names datatypename builtinname | usergenname builtinname Name | QName | NCName | ID | IDREF |IDREFS | NMTOKEN | NMTOKENS | ENTITY | ENTITIES | string | uri | timeInstant | timeDuration | recurringInstant binary | float | double | decimal |integer | non-negative-integer | positive-integer | non-positive-integer | negative-integer | date | time | language usergenname datatypeRef

The datatypename production above is not to be confused with that labeled datatypeName in .

Facets ordered bounds? numeric? dateTime? unordered pattern? enumeration? length? minlength? maxlength? encoding? Ordered facets bounds (minInclusive | maxInclusive)? (minExclusive | maxExclusive)? maxInclusive literalValue minInclusive literalValue minExclusive literalValue maxExclusive literalValue Literal type

The literal value give must be of the same type as the datatype as the basetype given in the datatype definition in which this facet appears.

Numeric facets numeric precision? scale? precision integerLiteral scale integerLiteral dateTime facets dateTime period? period timeDurationLiteral

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)

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This type could just as well have been defined with the potential type "currency" (defined above) as its .

Unordered facets length integerLiteral minlength integerLiteral maxlength integerLiteral enumeration literal+ pattern regularExpression | IS08601picture encoding 'hex' | 'base64'

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 ]]> Literals literal literalValue literalValue stringLiteral | numericLiteral | dateTimeLiteral | uriLiteral |