NOTE: These slides have not been updated since 2003. They have been superseded by the book An Introduction to XML and Web Technologies Addison-Wesley, and the accompanying online material. Please see http://www.brics.dk/ixwt/ for more information. Anders Møller and Michael Schwartzbach, February 2006

THE XML REVOLUTION  -  TECHNOLOGIES FOR THE FUTURE WEB

Namespaces

XML Schema

• uses namespaces itself - to distinguish schema instructions from the language we are describing
• supports namespace assigning - by associating a target namespace to the language we are describing

Example:

<schema xmlns="http://www.w3.org/2001/XMLSchema" xmlns:b="http://businesscard.org" targetNamespace="http://businesscard.org"> <element name="card" type="b:card_type"/> ... <complexType name="card_type"> <sequence> <element ref="b:name"/> ... </sequence> </complexType> ... </schema>

• the default namespace is that of XML Schema (such that e.g. complexType is considered an XML Schema element)
• the target namespace is our business card namespace
• the b prefix also denotes our business card namespace (such that we can refer to target language constructs from within the schema)

Unfortunately, XML Schema has a rather unconventional use of namespaces:

• prefixes in attribute values (e.g. ref="b:name") - the namespace spec does not tell how to resolve this
• a notion of "unqualified locals" (which is even a default) - allowing prefixes to be omitted from locally declared elements in instance documents
  (for a reasonable semantics, always use elementFormDefault="qualified" if using local definitions)

COPYRIGHT © 2000-2003 ANDERS MØLLER & MICHAEL I. SCHWARTZBACH