The XML libraries and tools

• Libxml2: the core XML Library
• Libxslt: the XSLT-1.0 Library
• LibExslt: the XSLT Extensions Library
• XMLSig: the XML signature and encryption Library
• xmllint: CLI tool for libxml2
• xmlcatalog: CLI tool for XML catalog handling
• xsltproc: CLI tool for XSLT transformations

Architecture of libxml2

Big improvements

• New parsing interface: xmlReader
• New validation code: Relax-NG, W3C Schemas (incomplete)
• Streaming validation: DTD and Relax-NG
• Deploying the thread support, large files
• Finished XInclude, XML Base support
• Even larger API: 1200+ functions

Deployment

Very diverse use cases:

• Largely deployed on Linux/BSDs: Gnome, KDE, DocBook
• Libxml2 part of Solaris 9
• A lot of Windows users
• Industrial use: financial sector, communication, web and publishing
• The Perl and Python bindings are popular
• xmlSig is ready for deployment too: post 1.0
• Known to work on a dozen of OSes

The reader interface

• Used to process large documents
• Based on C# xmlReader interface
• Simpler to program: iterator over the document nodes
• Allows validation

import libxml2

reader = libxml2.newTextReaderFilename("ex.xml")
ret = reader.Read()
while ret == 1:
    print reader.Name()
    ret = reader.Read()

Relax-NG: the specification

More extensive validation than DTDs

Counter proposal to W3C XML Schemas

• online: smaller, clearer, simpler
• more document oriented
• good tutorial is available
• work done at OASIS, in progress to become and ISO standard
• allow reuse of W3C XML Schemas datatypes

Basic example

Consider some simple XML:

<addressBook>
  <card>
    <name>John Smith</name>
    <email>js@example.com</email>
  </card>
  <card>
    <name>Fred Bloggs</name>
    <email>fb@example.net</email>
  </card>
</addressBook>

Basic DTD

The DTD for it:

<!DOCTYPE addressBook [
<!ELEMENT addressBook (card*)>
<!ELEMENT card (name, email)>
<!ELEMENT name (#PCDATA)>
<!ELEMENT email (#PCDATA)>
]>

Basic Relax-NG schema

The Relax-NG schema for it:

<element name="addressBook" xmlns="http://relaxng.org/ns/structure/1.0">
  <zeroOrMore>
    <element name="card">
      <element name="name">
        <text/>
      </element>
      <element name="email">
        <text/>
      </element>
    </element>
  </zeroOrMore>
</element>

Using attributes

If using attributes:

<element name="card">
  <attribute name="name">
    <text/>
  </attribute>
  <attribute name="email">
    <text/>
  </attribute>
</element>

Unified model

Relax-NG has an unified model for attributes and elements.

Using attributes or elements:

<element name="card">
  <choice>
    <element name="name">
      <text/>
    </element>
    <attribute name="name">
      <text/>
    </attribute>
  </choice>
  <choice>
    <element name="email">
      <text/>
    </element>
    <attribute name="email">
      <text/>
    </attribute>
  </choice>
</element>

Type checkig

Relax-NG allows to type-check textual content

Reuse of the W3C XML Schemas Datatype library

Block reuse

Modular structure using includes

Use the define and ref to reuse blocks

<element name="card">
  <ref name="cardContent"/>
</element>
...
<define name="cardContent">
  <element name="name">
    <text/>
  </element>
  <element name="email">
    <text/>
  </element>
</define>

Roadmap

• Finish XML Schemas, some xmlReader extensions
• Work on XML and XML Namespace : 1.1
• Evaluate XPath2 and XSLT2 for implementation
• Documentation: more examples

Questions and Answers