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.

INTERFACE

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

Call this method to create a new XML::Validator:Schema object. The only requied option is file which is required and 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 $@;
```

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>

<extension>

  Supported attributes: base

  Notes: only allowed inside <simpleContent>

<simpleType>

  Supported attributes: name

<restriction>

  Supported attributes: base

<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

<annotation>

<documentation>

  Supported attributes: name

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 totalDigits, fractionDigits and enumeration facets are
 not supported on decimal or any types derived from decimal (all
 numeric types).

integer

int

short

byte

unsignedInt

unsignedShort

unsignedByte

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

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:

Line and column numbers are not included in the generated error messages. This will change as soon as XML::Filter::ExceptionLocator is ready for action.
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

AUTHOR

Sam Tregar <sam@tregar.com>

COPYRIGHT AND LICENSE

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.

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