PHP web applications development at the speed of light
This page was last updated
Wednesday 24 September 2003
eXtensible Markup Language (XML) is an industry standard offering data
encapsulation mechanisms for IT systems. Because it facilitates the
development of arbitary schemas (vocabularies) within it's framework, other satelite
standards based on XML are also available. Since XAO encourages the use
of standards based web applications development, it is appropriate to
list some of the XML based standards affecting web development.
- eXtensible Markup Language (XML) W3C website
"Extensible Markup Language (XML) is a simple, very flexible
text format derived from SGML (ISO 8879). Originally designed to
meet the challenges of large-scale electronic publishing, XML is
also playing an increasingly important role in the exchange of a
wide variety of data on the Web and elsewhere."
- an absolute fantastic place for the newbie to start
- another good learning place.
- xml.org - run by the
Organization for the Advancement of Structured Information
- xml.com - lots of news and
articles specifically XML related.
- XML schema
XML Schemas express shared vocabularies and allow machines to carry
out rules made by people. They provide a means for defining the
structure, content and semantics of XML documents.
Schema definition files can be used to validate XML datagrams.
These vocabularies/schema-definitions themselves often form the
basis of other standards.
Docbook is a standard established in the publishing industry for the
purposes of marking up documents and books. It often forms the basis
of good content management systems. We plan to use docbook as the
format for marking up documentation in the XSLT files that will go
into the XSLT library distributed with XAO.
This standard forms the basis of what people refer to as "Web
Services". The SOAP specification provides a good example of
XML employed as a data encapsulation technique for datagrams subject
to transmission over various widely available protocols.
While the overhead of using XML is very high, it's
wide-spread adoption makes it a powerful option for remote method
invocations/client-server requests. Perfromance is sacrificed for
- XML:DB Initiative for XML Databases
The XML format lends itself to structures not easily replicated in
traditional database systems such as relational database management
systems (RDBMS (SQL databases)). Pure XML databases are
rapidly gaining popularity as an acceptable alternative to RDBMSs
for mass data storage of cirtain types of data. While not replacing
RDBMSs or competing with them head-on, pure XML databases
provide advantages in cirtain circumstances. For instance,
the tend to be more suited to situations where it's not entirely
possible to predict the structure of the data to be stored. Also,
the query mechanism employed is more suitable for lookups on
heirachial data structures and even unstructured data. They are not
good at storing relational data the way RDBMSs are. Hence,
applications will often adopt them in addition to
traditional RDBMSs. While utilising existing XML standards such as
XPath, they have
neccecitated the introduction of at least one new standard -
- Xindice - open source
- Xindice was born out of the first open-source attempt at a pure-XML
database. Anyone considdering building a content management system
with XAO would do well to considder using Xindice for document storage
(perhaps encoding the documents in Docbook). XAO will provide a Xindice
object specifically for interacting with this service.
- XSLT (dedicated links page)
- Since it is used so extensively by XAO users, it has it's own
dedicated links page on this site.