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Authoring Schemas With XSD
Dare Obasanjo points to his own "article on O'Reilly's XML.com that specifies a set of guidlelines for authoring schemas using the W3C XML Schema Definition language commonly abbreviated as XSD. The primary theme is embracing simplicity by showing how to avoid the more complex and esoteric features of the language."
I've found XML to be useful for data transfer and syndication. I haven't looked into building sites with it, but it's handy to have Company A export their data so Company B and Company C can use it. I work on a site that displays pricing and availability of houses using XML data exported from a third party in XML. It's also widely used in weblogs (save the flames) and news sites so people can syndicate the content.
When the W3C XML Schema recommendation was first released, there were certain parties whom overwhelmed by its newness, complexity and buggy implementations began to advocate using as few features as possible which culminated in the article W3C XML Schema Made Simple by Kohsuke Kawaguchi. However, a year later with parser implementations getting up to speed and more people using the technology it is clear that a number of the earlier misgivings about using some parts of the technology were misguided.
This is very similar to the situation with Mozilla and C++. In 1998, a few months after the ISO standard was ratified a set of guidelines for using C++ were specified by the Mozilla team which included rules like don't use templates, don't use exceptions, and don't use namespaces. Since then the Mozilla team has looked back at their decision and realized that some of the decisions they made were unwise specifically listed as mistakes were avoiding exceptions and templates. I truly commend the Mozilla team for making their post mortem available online for other [C++ or otherwise based] software development projects to learn from.
This article aims to do the same thing for the XML community and the W3C XML Schema recommendation.
You wont see XML show up in web browsers for a while, HTML still does the job on the client side. I have been writing applications in the XML/Java space for 2+ years. The uses of XML are countless, XML Schemas provide the meta information needed by applications that use XML. Most of the XML apps I've written are in the enterprise application-to-application area, but Ive found use for it almost everywhere else. Any application that needs its data to be descriptive and portable can use XML. Many high end user apps store information primarily in XML, the ones that don't probably will soon. The problem remains that many people dont understand the need for XML and descriptive data.
XSD is a Language for describing XML documents. Whats not a language about that? Its more of a grammar, so maybe you have a point. Schemas dont actually DO anything (neither does XSLT on its own) they just describe to you (or your application) the semantics and structure of an XML document, so a grammar would be more appropriate. The use of 'language' confuses newbies into thinking that XSD is a programming language and has the same set of responsibilities as a pl.
XML is good for industry standards bodies. It's open, there are open implementations, and you can irrefutably lay down the syntactic and semantic law in a schema without any ambiguity.
FpML, ArApXML, MDML are good examples of industry-specific XML standards. Going into the wider space, you get ebXML, SOAP and more.
XML is the new-world replacement for EDI (Electronic Data Interchange) and it's biggest uses are B2B and company-internal, with a small B2C following starting up for things like weather data, news feeds etc. It's not surprising you've not come across it... and until you go and work for a megalithic corporation on the IT side, you probably won't.
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I think they already have a copy. The author, Dare Obasanjo, works for them.
I watched C-beams glitter in the dark near the Tannhauser gate.
I'm not sure how much traffic they get these days, but the InfoWorld website is XML based. I believe it uses server-side XSLT transforms to turn XML into HTML.
Also, don't assume that just because the URLs don't have ".xml" in them that the site isn't using XML - it's often transparent, such as when using Apache Cocoon
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SERENITY NOW!!!!!!!!!!!!!!!!
Dark Age of Camelot uses XML to display the character stats.
Here is the display page and here is the XML source.
This page explains how they do it. Very nifty for making guild web pages using their data.
Take a look at www.gentoo.org The whole site uses XML.
Also check out Daniel's articles for IBM developerWorks describing the site... Part 1 Part 2 Part 3 Part 4Moreover, XML itself is intended only to express content. It is standards built on top of XML (such as XHTML), that define how that content should appear. Many websites use XHTML, but the casual observer would not notice -- the source code of the page is nearly identical.
In all of the three programming internships I've held (I'm still in college), XML was the underlying technology.
Try Relax NG. Relax was developed in Japan and is quite popular there. TREX is James Clark's attempt at a type system that is more flexible than DTDs but less complicated than XML Schema. Relax NG is the merger of those two systems. It looks appealing but I have not used it in anger yet.
Not to mention testing is much easier. I can capture an input call to the API created by whatever client program is being used and hack it with my favorite text editor to test.
And as another person mentioned, xml can be used by a far larger range of programming languages and tools than CORBA bindings.
I'd also contend that xsd files are far easier to understand than IDL.
Check out tldp.org. All the documents are created usi ng XML/SGML. The idea offcourse is to ultimately create structured content, that can be queried and linked in future.
Consensus is good, but informed dictatorship is better