The world of XML and Web services is huge, and growing. developerWorks does much to map it out for you, but when you're looking for a schema or a public Web service to meet some pressing need, it's useful to have handy several key resources. In the early years of XML, James Tauber's SCHEMA.NET was a great one-stop shop, but it has fallen into disrepair. No single resource covers the entire universe, but collectively the sites I list here can save you from reinvention, or even giving up on a need altogether.

Finding XML schemata

In my article, "A survey of XML standards: Part 3", I gathered together discussion of the most important general-purpose XML schemata. I recommend that you become familiar with at least the basics of all those schemata, as a sort of foundation. See also the master article of my XML standards survey. developerWorks also hosts a technical library of XML standards, which primarily focuses on the XML vocabularies that would be of interest to most developers.

When it comes to comprehensive coverage, it's hard to beat XML.org, and in particular The Cover Pages. Robin Cover, who maintains the resource, was honored by his peers this year with the XML Cup for his long chronicling of XML (and SGML) standards. The easiest way to filter The Cover Pages to find only schemata is by reference to the XML Applications and Initiatives page. Overall, The Cover Pages offer so much volume that it doesn't necessarily make the best quick reference, but it is a good place to go to find the details on some schema you've heard about. However the parent page, XML.org, has a Schemas/DTD Registry, organized by topic and searchable by keyword.

One way to find XML schemata is to search for the instances and work backwards. Standard search technologies can help here. Bob DuCharme's article "Googling for XML" offers some very interesting and useful tips on how to conduct such searches with the most popular engine. Google also provides a useful resource in its Google Directory index for XML.

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Finding Web services and RDF schemata

The best known source for finding public SOAP Web services is XMethods. It has a comprehensive list of SOAP services that you can sort by several criteria. It also provides a demo client so you can try out the services right from the index site. You can also keep track of the listings on XMethods programmatically using UDDI, RSS, and other means. IBM provides a public (free, but requiring registration) UDDI registry. As it says "[y]ou can describe your business, discover business partners, and use the UDDI technical standards to communicate with the world." Naturally one of the things you can do is look up or register the Web services you make available in public or private.

Other sites that provide directories of Web services include RemoteMethods.com and Web Service List. A chronicle of interesting Web services is Web service of the Day.

One resource that straddles the Web services/Semantic Web is WSindex.org, a directory of Web services, XML, SOAP, UDDI, WSDL, and Semantic Web resources. This site is a hierarchical and searchable directory. The Web Services node has listings of many publicly-available services. The Semantic Web node is really just an index of resources about the Semantic Web, and not of actual Semantic Web content or schemata. The XML Schema node does indeed offer a directory of XML schemata.

For RDF, OWL, and other Semantic Web schemata, make SchemaWeb your first stop. This site is a searchable directory and chronicle of Semantic Web schemata, which you can access with RDF query. Another important stop is Bob DuCharme's rdfdata.org, which was born of his own search for public RDF on the Web.

Resources

• Keep an eye on SCHEMA.NET, formerly a great compendium of XML schemata. James Tauber recently posted the following message: "I've received enough expressions of interest to prompt me to bring back SCHEMA.NET. The next few weeks will be spent gathering updated information and putting together the site infrastructure."
  
  
• Check out John E. Simpson's XML Tourist column, where he showcases lesser known XML applications serving various communities.
  
  
• If you need to manage a registry of your own, learn about the IBM alphaWorks XML Registry , "a data management system that manages and provides services for XML artifacts, including schemas (DTD, XSD), stylesheets (XSL) and instance documents (WSDL, WSFL, XML). XML Registry can be used to obtain an XML artifact automatically, to search or browse for an XML artifact, to deposit an XML artifact with or without related data, and to register an XML artifact without deposit."
  
  
• Find more XML resources on the developerWorks XML zone, including Uche Ogbuji's Thinking XML column, where he covers many XML and metadata specifications and registries.
  
  
• For a complete list of XML tips to date, check out the tips summary page.
  
  
• Browse for books on these and other technical topics.
  
  
• And, of course, the developerWorks SOA and Web services zone offers a treasure trove of Web services information. The "New to SOA and Web services" page is an excellent place to get started.
  
  
• Find out how you can become an IBM Certified Developer in XML and related technologies.
  
  

About the author

Uche Ogbuji is a consultant and co-founder of Fourthought Inc., a consulting firm specializing in XML solutions for enterprise knowledge management applications. Fourthought develops 4Suite, the open source platform for XML middleware. Mr. Ogbuji is a Computer Engineer and writer born in Nigeria, living and working in Boulder, Colorado, USA. You can reach him at uche@ogbuji.net.

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Table of contents

• Finding XML schemata
• Finding Web services and RDF schemata
• Resources
• About the author
• Comments

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