Schema(3) User Contributed Perl Documentation Schema(3)NAMEXML::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 recommeded!
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/
perl v5.14.1 2008-01-31 Schema(3)
