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XForms is an XML application that represents the next generation of forms for the Web. This document specifies the requirements for XForms 1.1.
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This document is a W3C Working Group Note, made available by the W3C XForms Working Group as part of the XForms Activity within the W3C Interaction Domain. The authors of this document are the XForms Working Group participants.
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XForms 1.1 will build upon the solid foundation set forth by XForms 1.0 - the Next Generation of Web Forms. This version makes incremental improvements over version 1.0 to provide expanded behaviors for the existing and established XForms Model-View-Controller Framework and by embracing SOAP. This version also makes adjustments to XForms to facilitate its adoption in other host languages.
Requirement: Support SOAP as a new method of submission.
In XForms 1.0, the submission element allows sending part of
any instance to the server, but there is no reciprocal functionality for
handling the returned data. In particular, there is no ability to pass
partial instance data back and forth between client and server based on
conditions expressed via XForms model properties and/or triggered by user
interactions.
Requirement: Allow the submission element to specify
that the returned data can go in any instance, not just the instance from
which the submitted data was drawn.
Requirement: Allow the submission element to specify
that the returned data can be used to replace a node in the instance data. A
use case would be submitting an element containing a UK postal code and
having the returned data replace an instance subtree containing an
address.
In XForms 1.0, a repeat element creates the user interface
elements in its content once for each node in the collection indicated by its
nodeset attribute. If the nodeset expression
results in an empty collection, then no user interface elements are
created.
To dynamically add user interface elements as more data becomes available,
insert is used to add another node to the collection to which
the repeat nodeset is bound. However, the insert
element in XForms 1.0 requires that the collection contain a prototypical
node in the initial instance data that is to be duplicated in the
collection.
Due to this architecture, it is not possible to use insert on
a repeat collection that is initially empty. The use case for an
initially empty collection is a shopping cart application, where the user
expects to start with an empty shopping cart.
Secondly, it is also more difficult to express forms in which the data
content is derived not from the prototypical instance but from other instance
data obtained after initialization. Each leaf node in the subtree rooted by
the new node in the repeat collection must currently be filled
with a separate invocation of setvalue even if the desired
subtree structure exists elsewhere in instance data.
Requirement: Allow a method for copying a subtree of instance data (identified by a single apex element node) and pasting the subtree copy into an identified instance element node. The method must provide a facility for indicating where to put the subtree copy in the children of the target node (e.g. first, last, after a given child).
The XForms 1.0 Schema currently allows bind elements to be
nested. One capability of nested binds is that an outer bind can
provide the XPath nodeset against which an inner bind operates
to provide various model item properties.
In XForms 1.0, user interface elements can indicate an XPath node or
nodeset using ref or nodeset. Alternately, a
bind attribute can be used to indicate by IDREF a
bind element whose whose XPath nodeset is to be used with the
user interface element.
Other than the possible issue of referring to a bind in another model, a
bind element should be able to reference another
bind element to provide a starting XPath nodeset with the same
effect as if the former bind had been nested within the
latter.
Requirement:Allow a bind element to use a
bind attribute to obtain its starting XPath nodeset from another
bind element.
A use case for this requirement is to allow forms processing systems to separate business rules (the 'inner' binds that specify computed model item properties) from database rules (the 'outer' binds that specify data locations within the instance). Forms management systems could then construct forms more easily since the business rules could simply be concatenated to the database rules if the former referred to the latter by ID reference rather than having to be nested within them.
Requirement: Let email address be a primitive (recognized) XForms datatype for schema data validation.
XForms expresses a processing model and user interface for the
modification of data expressed in XML. Currently, the XML can be obtained
from within the document or from a server. It would be useful to allow XForms
processors to edit XML obtained from the local computer, and to return the
edited XML to the local computer. To avoid security issues, this cannot be
done by simply using a file scheme in the src
attribute of the XForms instance element.
Requirement: Allow an XForms processor to provide an XML editing capability.
Applications that require mathematical exponentiation (raising X to the power Y) are not possible in XForms 1.0, such as the compounded interest calculation for a periodic loan payment.
Requirement: Allow the ability to calculate XY in XForms computational expressions.
The ability to reuse the XPath node-set referenced by a bind
has proven to be a valuable and powerful capability. For example, the XPath
node-set referenced by a bind can be used by another
bind or by a user interface element. It is useful to extend this
referencing capability to XPath expressions.
Requirement: Allow the ability to obtain the XPath node-set
associated with an identified bind from within an XPath
expression.
In some forms, it is necessary to perform a simple table lookup based on
user input. For example, suppose a form contains an element
conversionTable that provides conversion rates for various
currencies to the user's local currency. Based on the conversion selected by
the user, the appropriate exchange rate would be used in a calculation.
XPath provides the ability to perform this type of search using
predicates. To continue the above example, suppose each child of
conversionTable is a rate element with the exchange
rate as content and a currency attribute. Further, let a
separate instance element called currency provide the storage
for the currency selected by the user, and let amount contain
the amount to convert. The converted amount could then be obtained using the
following XPath: /root/amount *
/root/conversionTable/rate[@currency=/root/currency].
The problem with this approach is that it uses absolute referencing to obtain the currency value selected by the user. If the converted amount, amount, and currency elements were moved to a deeper point in the instance data, then the XPath would have to be rewritten.
Requirement: Allow an XPath expression to perform a table search using a key whose value is referenced relative to the initial context node of the XPath expression.
To increase widespread adoption of XForms in web applications, it is necessary to reduce the difficulty of authoring XForms in XHTML, which is currently hindered by the incessant need to flip between the host language namespace and the XForms namespace when authoring the user interface component of a form.
Requirement: Simplify Authoring XForms in XHTML2.
To facilitate the adoption of XForms in other XML tag sets, which is stated as a key goal in the XForms 1.0 requirements, implementation support for the XForms model will be a conformance level formally recognized by a distinct namespace from the XForms user interface related elements and attributes.
Requirement: Let the XForms 1.1 namespace be applied to the XForms 1.1 model, and let the XForms user interface related elements and attributes be defined abstractly so they can appear in a separate namespace or in the namespace of each host language.
This document was produced with the participation of current XForms Working Group participants: