Skip to Main Content
XML Schema
book

XML Schema

by Eric van der Vlist
June 2002
Intermediate to advanced content levelIntermediate to advanced
396 pages
11h 8m
English
O'Reilly Media, Inc.
Content preview from XML Schema

Name

xs:field — Definition of the field to use for a uniqueness constraint.

Synopsis

<xs:field
           id             = xs:ID
           xpath          = xs:token
           {any attributes with non-schema namespace}
           >
           Content: (xs:annotation?)
</xs:field>

May be included in: xs:key, xs:keyref, xs:unique

Description

xs:field is used to define the location of the fields on which a uniqueness constraint or reference will be checked.

The fields are elements or attributes that are identified by relative XPath expressions (i.e., xpath attributes) evaluated against the nodes selected by the xs:selector element.

Concatenated keys can be expressed defining multiple fields under a xs:unique, xs:key, or xs:keyref element.

Restrictions

The xpath attribute uses a simple subset of XPath 1.0. The motivation of the W3C XML Schema Working Group for defining this subset is to simplify the work of the implementers of schema processors, and also to define a subset that constraints the path to stay within the scope of the current element.

This subset is restricted to using only the child, attribute, self, and descendant or self XPath axes through their abbreviated syntaxes without including any test in any of the XPath location steps, and without using any XPath functions. It is identical to the subset defined for xs:selector, except that attributes are allowed in xs:field and forbidden in xs:selector.

The formal extended BNF given in the W3C Recommendation is as follows:

Field ::= Path ( '|' Path )* Path ::= ('.//')? ( Step '/' )* ( Step | '@' NameTest ...
Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
and much more.
Start your free trial

You might also like

XML in a Nutshell, 3rd Edition

XML in a Nutshell, 3rd Edition

Elliotte Rusty Harold, W. Scott Means
Beginning XML, 5th Edition

Beginning XML, 5th Edition

Danny Ayers, Liam R.E. Quin, Joe Fawcett
XML Schema Complete Reference, The

XML Schema Complete Reference, The

Cliff Binstock, Chris Galtenberg, Mike Wooding, Chris Dix, Mitchell Smith, Dave Peterson
Programming Web Services with SOAP

Programming Web Services with SOAP

James Snell, Doug Tidwell, Pavel Kulchenko

Publisher Resources

ISBN: 0596002521Supplemental ContentErrata Page