<<It has been a while since my article on standards related to web
services so I think it is time to take a look at recent activity by
some of the significant standards publishing organizations, starting
with the W3C. The W3C continues to be the main organization for
creation of internationally recognized standards for XML, WSDL, and
HTML. At any given time, a large number of related standards are
working their way through the standardization process in various
states of finality. W3C publications occur in a bewildering variety of
flavors: notes, drafts, candidate recommendation, proposed
recommendation and finally W3C Recommendation, essentially a standard.
XML
The current version of the XML 1.0 standard is the fourth edition.
This edition of the recommendation reached final form in August 2006.
XML version 1.1 recommendation (2nd edition) was also published at the
same time but does not seem to have been adopted widely. In fact,
Microsoft has chosen not to support 1.1 since it is not backwards
compatible with 1.0.
The fifth edition of XML 1.0 is currently in the form of a "proposed
recommendation" draft published in Feruary 2008. It includes some
changes defining the characters not allowed in element and attribute
names which first appeared in XML 1.1. The fifth edition might be
regarded as an attempt to save these XML 1.1 improvements from
obscurity. You may need to pay attention to this edition if you need
to make use of some foreign language character sets and other special
characters.
WSDL 2.0
WSDL, the Web Services Description Language, version 1, has been
sucessfully utilized in a variety of SOAP toolkits for a variety of
computer languages to automate creation of basic client and server
code. The current edition, version 1.1, was published published as a
W3C "note" in March 2001, before interest in RESTful style web
services really got started.
Workers on the next version of WSDL, originally called 1.2, made so
many modifications that it became version 2.0, reaching W3C
"recommendation" status in June 2007. Version 2.0 makes major changes
in the approach to describing a web service, but continues to
emphasize SOAP. The published standard does not give any example of
RESTful service description, but this article at the IBM
developerworks site shows how to use WSDL 2.0 for that purpose. I also
found this wikipedia article giving an example WSDL describing a REST
style web service implementing GET, POST, PUT, and DELETE methods.
XQuery and XPath
The W3C groups several standards for manipulating XML documents in the
Extensible Stylesheet Language Family (XSL). The complex interactions
of various XML related standards mean that none of these standards
evolves in isolation and the requirements of one frequently suggest
improvements to others. Here is an abbreviated list of some of these
interacting standards:
* XSLT The language for transforming XML documents, typically for
presentation. The most mature standard, dating from 1999.
* XPath The language for access to selected parts of an XML
document, used in both XSLT and XQuery.
* XQuery The language for expressing database query style
operations on XML documents.
* XML Schema The language used to define data types used in XML,
dating from 2004.
* XDM The Data Model used by XPath and XQuery.
The original (1999) XPath 1.0 specification has stood up well, but as
with so many W3C recommendations, work on a 2.0 version continued,
resulting in a formal 2.0 recommendation in January 2007. XQuery,
XPath 2.0 and XSLT 2.0 share a common "Data Model" also published in
January 2007. The data model refines the basic XML standard to
describe the representation of all legal values in XML document nodes,
and how expressions evaluate them, but it is not tied to any
particular computer language representation. As an example of how
standards evolve and interact, the Data Model working group found it
necessary to add additional types to the XML Schema language list of
allowed primitive types. Presumably the XML Schema Datatypes
recommendation will eventually catch up.
XQuery provides a simplified toolkit to extract data from XML
formatted data sources with a specially formatted query statement.
These statements are similar to SQL statements used with relational
databases and will look quite familiar to SQL programmers. XQuery
depends on the syntax of XPath 2.0 expressions to locate XML items. An
XQuery/XPath expression can replace many lines of Java code but this
convenience comes at a performance cost. This is not surprising since
an XPath tool has to both interpret the expression and navigate
through the XML document.
The W3C has released several important draft standards related to
XQuery in 2008. XQuery version 1.1 reached working draft status in
July. At the present time this version extends 1.0 with a "small
number of new features" related to grouping search results.
What is the significance of these standards?
That is a really good question! Some W3C standardization efforts have
had a great impact on the development of the web and web services,
while others, such as XML 1.1, are generally ignored. In some cases,
publications which never reached the formal "W3C Recommendation"
stage, such as WSDL 1.1, have been accepted as standards without
question by the industry. In my opinion, the developments in the
XQuery and XPath are going to be the most significant since they
vastly simplify working with the world's ever increasing volume of XML
formatted data.>>
You can read this at:
http://searchsoa.techtarget.com/tip/0,289483,sid26_gci1338544,00.html?track=NL-449&ad=671968&asrc=EM_NLT_4995436&uid=5532089
Gervas
