Horn-tooting time. XMLhack just hit 1,000 XML stories. Time to
And to compensate for this interruption to normal programming, here's an
interesting bit from XMLhack about James Clark's latest baby, the TREX
schema language. Yes, now we have three. W3C, ISO RELAX, and TREX.
TREX is at http://www.thaiopensource.com/trex/
Story from http://xmlhack.com/read.php?item=981
James Clark has announced Tree Regular Expressions for XML (TREX) a new
simple and flexible schema language focusing on the structure of XML
The new language is an attempt to define the tree structure of XML
documents without describing the data types or modifying anything in its
Calling it a schema language is perhaps misleading: it's goal is purely
validation. It doesn't aim to assist in interpreting or processing the
document. The post-validation infoset is exactly the same as the
James Clark also mentions that "TREX expects to partner with a
datatyping language, such as XML Schema Part 2: Datatypes".
TREX appears then as an alternative to W3C XML Schema Part 1.
Interestingly, some issues on which James Clark had expressed his
disapproval are addressed by TREX which includes some highly flexible
features such as:
Attributes can be defined before, after or between elements.
Choices between elements and attributes can be defined (a feature that
might help defining RDF TREX schemas).
Choices between elements and PCDATA can be defined (a feature needed to
define a schema for XSLT).
Unordered element sequences can be defined without much restriction.
The TREX specification is available with a tutorial, a sample Java
implementation, a stylesheet to convert Relax schemas into TREX and TREX
schemas including those for TREX, XSLT1.0, Relax Core and Xlink.
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