NAME

       XML::Validator::Schema - validate XML against a subset of W3C XML Schema

SYNOPSIS

         use XML::SAX::ParserFactory;
         use XML::Validator::Schema;

         #
         # create a new validator object, using foo.xsd
         #
         $validator = XML::Validator::Schema->new(file => 'foo.xsd');

         #
         # create a SAX parser and assign the validator as a Handler
         #
         $parser = XML::SAX::ParserFactory->parser(Handler => $validator);

         #
         # validate foo.xml against foo.xsd
         #
         eval { $parser->parse_uri('foo.xml') };
         die "File failed validation: $@" if $@;

DESCRIPTION

       This module allows you to validate XML documents against a W3C XML Schema.  This module does not
       implement the full W3C XML Schema recommendation (http://www.w3.org/XML/Schema), but a useful subset.
       See the SCHEMA SUPPORT section below.

       IMPORTANT NOTE: To get line and column numbers in the error messages generated by this module you must
       install XML::Filter::ExceptionLocator and use XML::SAX::ExpatXS as your SAX parser.  This module is much
       more useful if you can tell where your errors are, so using these modules is highly recommended!

INTERFACE

       •   "XML::Validator::Schema->new(file => 'file.xsd', cache => 1)"

           Call this method to create a new XML::Validator:Schema object.  The only required option is "file"
           which must provide a path to an XML Schema document.

           Setting the optional "cache" parameter to 1 causes XML::Validator::Schema to keep a copy of the
           schema parse tree in memory.  The tree will be reused on subsequent calls with the same "file"
           parameter, as long as the mtime on the schema file hasn't changed.  This can save a lot of time if
           you're validating many documents against a single schema.

           Since XML::Validator::Schema is a SAX filter you will normally pass this object to a SAX parser:

             $validator = XML::Validator::Schema->new(file => 'foo.xsd');
             $parser = XML::SAX::ParserFactory->parser(Handler => $validator);

           Then you can proceed to validate files using the parser:

             eval { $parser->parse_uri('foo.xml') };
             die "File failed validation: $@" if $@;

           Setting the optional "debug" parameter to 1 causes XML::Validator::Schema to output elements and
           associated attributes while parsing and validating the XML document. This provides useful information
           on the position where the validation failed (although not at useful as the line and column numbers
           included when XML::Filter::ExceptiionLocator and XML::SAX::ExpatXS are used).

RATIONALE

       I'm writing a piece of software which uses Xerces/C++ ( http://xml.apache.org/xerces-c/ ) to validate
       documents against XML Schema schemas.  This works very well, but I'd like to release my project to the
       world.  Requiring users to install Xerces is simply too onerous a requirement; few will have it already
       and the Xerces installation system leaves much to be desired.

       On CPAN, the only available XML Schema validator is XML::Schema.  Unfortunately, this module isn't ready
       for use as it lacks the ability to actually parse the XML Schema document format!  I looked into
       enhancing XML::Schema but I must admit that I'm not smart enough to understand the code...  One day, when
       XML::Schema is completed I will replace this module with a wrapper around it.

       This module represents my attempt to support enough XML Schema syntax to be useful without attempting to
       tackle the full standard.  I'm sure this will mean that it can't be used in all situations, but hopefully
       that won't prevent it from being used at all.

SCHEMA SUPPORT

   Supported Elements
       The following elements are supported by the XML Schema parser.  If you don't see an element or an
       attribute here then you definitely can't use it in a schema document.

       You can expect that the schema document parser will produce an error if you include elements which are
       not supported.  However, unsupported attributes may be silently ignored.  This should not be misconstrued
       as a feature and will eventually be fixed.

       All of these elements must be in the http://www.w3.org/2001/XMLSchema namespace, either using a default
       namespace or a prefix.

         <schema>

            Supported attributes: targetNamespace, elementFormDefault,
            attributeFormDefault

            Notes: the only supported values for elementFormDefault and
            attributeFormDefault are "unqualified."  As such, targetNamespace
            is essentially ignored.

         <element name="foo">

            Supported attributes: name, type, minOccurs, maxOccurs, ref

         <attribute>

            Supported attributes: name, type, use, ref

         <sequence>

            Supported attributes: minOccurs, maxOccurs

         <choice>

            Supported attributes: minOccurs, maxOccurs

         <all>

            Supported attributes: minOccurs, maxOccurs

         <complexType>

           Supported attributes: name

         <simpleContent>

           The only supported sub-element is <extension>.

         <extension>

           Supported attributes: base

           Notes: only allowed inside <simpleContent>

         <simpleType>

           Supported attributes: name

         <restriction>

           Supported attributes: base

           Notes: only allowed inside <simpleType>

         <whiteSpace>

           Supported attributes: value

         <pattern>

           Supported attributes: value

         <enumeration>

           Supported attributes: value

         <length>

           Supported attributes: value

         <minLength>

           Supported attributes: value

         <maxLength>

           Supported attributes: value

         <minInclusive>

           Supported attributes: value

         <minExclusive>

           Supported attributes: value

         <maxInclusive>

           Supported attributes: value

         <maxExclusive>

           Supported attributes: value

         <totalDigits>

           Supported attributes: value

         <fractionDigits>

           Supported attributes: value

         <annotation>

         <documentation>

           Supported attributes: name

         <union>
           Supported attributes: MemberTypes

   Simple Type Support
       Supported built-in types are:

         string

         normalizedString

         token

         NMTOKEN

          Notes: the spec says NMTOKEN should only be used for attributes,
          but this rule is not enforced.

         boolean

         decimal

          Notes: the enumeration facet is not supported on decimal or any
          types derived from decimal.

         integer

         int

         short

         byte

         unsignedInt

         unsignedShort

         unsignedByte

         positiveInteger

         negativeInteger

         nonPositiveInteger

         nonNegativeInteger

         dateTime

           Notes: Although dateTime correctly validates the lexical format it does not
           offer comparison facets (min*, max*, enumeration).

         double

           Notes: Although double correctly validates the lexical format it
           does not offer comparison facets (min*, max*, enumeration).  Also,
           minimum and maximum constraints as described in the spec are not
           checked.

         float

           Notes: The restrictions on double support apply to float as well.

         duration

         time

         date

         gYearMonth

         gYear

         gMonthDay

         gDay

         gMonth

         hexBinary

         base64Binary

         anyURI

         QName

         NOTATION

   Miscellaneous Details
       Other known devations from the specification:

       •   Patterns specified in pattern simpleType restrictions are Perl regexes with none of the XML Schema
           extensions available.

       •   No effort is made to prevent the declaration of facets which "loosen" the restrictions on a type.
           This is a bug and will be fixed in a future release.  Until then types which attempt to loosen
           restrictions on their base class will behave unpredictably.

       •   No attempt has been made to exclude content models which are ambiguous, as the spec demands.  In
           fact, I don't see any compelling reason to do so, aside from strict compliance to the spec.  The
           content model implementaton uses regular expressions which should be able to handle loads of
           ambiguity without significant performance problems.

       •   Marking a facet "fixed" has no effect.

       •   SimpleTypes must come after their base types in the schema body.  For example, this is ok:

               <xs:simpleType name="foo">
                   <xs:restriction base="xs:string">
                       <xs:minLength value="10"/>
                   </xs:restriction>
               </xs:simpleType>
               <xs:simpleType name="foo_bar">
                   <xs:restriction base="foo">
                       <xs:length value="10"/>
                   </xs:restriction>
               </xs:simpleType>

           But this is not:

               <xs:simpleType name="foo_bar">
                   <xs:restriction base="foo">
                       <xs:length value="10"/>
                   </xs:restriction>
               </xs:simpleType>
               <xs:simpleType name="foo">
                   <xs:restriction base="xs:string">
                       <xs:minLength value="10"/>
                   </xs:restriction>
               </xs:simpleType>

CAVEATS

       Here are a few gotchas that you should know about:

       •   No Unicode testing has been performed, although it seems possible that the module will handle Unicode
           data correctly.

       •   Namespace processing is almost entirely missing from the module.

       •   Little work has been done to ensure that invalid schemas fail gracefully.  Until that is done you may
           want to develop your schemas using a more mature validator (like Xerces or XML Spy) before using them
           with this module.

BUGS

       Please use "rt.cpan.org" to report bugs in this module:

         http://rt.cpan.org

       Please note that I will delete bugs which merely point out the lack of support for a particular feature
       of XML Schema.  Those are feature requests, and believe me, I know we've got a long way to go.

SUPPORT

       This module is supported on the perl-xml mailing-list.  Please join the list if you have questions,
       suggestions or patches:

         http://listserv.activestate.com/mailman/listinfo/perl-xml

CVS

       If you'd like to help develop XML::Validator::Schema you'll want to check out a copy of the CVS tree:

         http://sourceforge.net/cvs/?group_id=89764

CREDITS

       The following people have contributed bug reports, test cases and/or code:

         Russell B Cecala (aka Plankton)
         David Wheeler
         Toby Long-Leather
         Mathieu
         h.bridge@fasol.fujitsu.com
         michael.jacob@schering.de
         josef@clubphoto.com
         adamk@ali.as
         Jean Flouret

AUTHOR

       Sam Tregar <sam@tregar.com>

COPYRIGHT AND LICENSE

       Copyright (C) 2002-2003 Sam Tregar

       This program is free software; you can redistribute it and/or modify it under the same terms as Perl 5
       itself.

A NOTE ON DEVELOPMENT METHODOLOGY

       This module isn't just an XML Schema validator, it's also a test of the Test Driven Development
       methodology.  I've been writing tests while I develop code for a while now, but TDD goes further by
       requiring tests to be written before code.  One consequence of this is that the module code may seem
       naive; it really is just enough code to pass the current test suite.  If I'm doing it right then there
       shouldn't be a single line of code that isn't directly related to passing a test.  As I add functionality
       (by way of writing tests) I'll refactor the code a great deal, but I won't add code only to support
       future development.

       For more information I recommend "Test Driven Development: By Example" by Kent Beck.

SEE ALSO

       XML::Schema

       http://www.w3.org/XML/Schema

       http://xml.apache.org/xerces-c/