 | Level: Intermediate Contributors: OASIS, ISO 06 Feb 2007
Updated 25 Apr 2007 RELAX NG is a grammar-based XML schema language used to
describe, define, and limit XML vocabularies. Find out why some people
dislike Document Type Definition (DTD), and discover how RELAX NG aims
to improve upon it.
RELAX
NG
[OASIS Committee Specification and ISO Standard ISO/IEC 19757-
2:2003] is an XML schema language, meaning it is a language that
you can use to define and limit XML vocabularies. The original XML
schema language is the DTD, defined in XML 1.0 itself. However, some
people dislike DTD for its awkward syntax, limitations in the text and
markup constructs it can express, and the difficulty of handling XML
Namespaces. Several new XML schema languages have emerged to supplant or
augment DTDs, including RELAX NG, which is renowned for its simplicity
and expressiveness. The core specification of RELAX NG defines an XML
syntax for schemata, but there is also a
RELAX NG Compact
Syntax
[OASIS Committee Specification and ISO Standard ISO/IEC
19757-2:2003/Amd.1:2006], which defines a simple text syntax for RELAX
NG schemata. The ISO versions of RELAX NG are now available for free
from ISO's Freely Available
Standards page.
Resources
- Read Nicholas Chase's introductory tutorial Understanding RELAX NG, which gets you up to speed on both
RELAX NG's simplicity and its power, including both its full XML-based
and its compact syntax (developerWorks, December 2003).
- David Mertz's XML Matters column on developerWorks focuses on
RELAX NG in his series "Kicking back with RELAX NG":
-
Part 1 looks at the general semantics of RELAX NG
and touches on datatyping (February 2003).
-
Part 2 continues the discussion by addressing a few
additional semantic issues and looking at tools for working with RELAX
NG (March 2003).
-
Part 3 explores the RELAX NG compact syntax in
detail and explains the exact correspondences between compact syntax and
XML syntax (May 2003).
- Take a look at the official tutorials for RELAX NG's core and its compact
syntax.
- ZVON offers a combined tutorial for RELAX
NG and W3C XML Schema language.
- Many resources are linked from the RELAX NG home page.
- ZVON offers a RELAX NG
Reference.
- One of the aspects of RELAX NG that might trip you up is
expressing simple text patterns, so Uche Ogbuji provides some guidance
in Tip: Use the right pattern for simple text in RELAX NG
(developerWorks, October 2005).
- RELAX NG allows you to define your own data types, as
demonstrated by Elliotte Rusty Harold in RELAX NG
with custom datatype libraries (developerWorks, November 2004).
- Read about other XML standards:
Index of XML
standards.
- Participate in any of several XML-centered forums:
XML
zone discussion forums.
- Get involved in the developerWorks community: developerWorks blogs
- Find out how you can become an IBM-Certified
Developer in XML and related technologies at IBM XML
certification.
- See the developerWorks XML Zone for a wide range of
technical articles and tips, tutorials, standards, and IBM Redbooks at
XML
technical library.
- Stay current with technology in these sessions: developerWorks technical events and webcasts.
- Build your next development project with trial
software available for download directly from developerWorks: IBM trial software
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