W3C XML schema

There are many ways to write schemas for XML documents, but only a few are commonly used. XML designers usually select from this triumvirate of schema languages Document Type Definition (DTD), W3C XML Schema, and RelaxNG. Sometimes they augment their validation with Schematron rules. 

W3C XML Schema is a schema language defined by the W3C (Thompson et al. 2004 Biron and Malhotra 2004). The choice of name for this schema language was very unfortunate. As discussed above, several schema languages can be used for validation of XML documents, and W3C XML Schema is just one of them. Unfortunately, many people do not understand this nuance and often insist on W3C XML Schemas in situations where another schema language would be more suitable. 

W3C XML Schema is a powerful validation language that is well supported by software tools, but it has some disadvantages that are important to keep in mind. Its specifications are very complex and difficult to thoroughly comprehend. This unfortunate fact led to many corrections to the original specifications, and many problems are still not fully resolved. Although people are shielded from this complexity by schema-authoring software, they become hostages to their tools. If a tool does not offer some validation rule, it may be very difficult to write it correctly by hand if... 

RelaxNG is a very powerful schema language that is much simpler to use and comprehend then W3C XML Schema. It is particularly suitable for validation of flexible data and for fast prototyping. This makes it the validation language of choice in data mining applications where diverse sources are processed and combined. 

In the heart of the language lies a flexible core applicable to many analytical techniques, as described by the W3C XML Schema. Specific needs of individual techniques are addressed in Analytical Technique Definition Documents that are XML files specifying particular parameters. The attempt to separate core features from particularities in a modular way is laudable. Other specification authors would benefit from using this approach. 

W3C, XML Schema Definition Language W3C XML Schema Working Group and Schema Specifications", http //www.w3.org/XML/Schema, 2004... 

The different dialects of XML (XHTML, KML) are constrained by XML schemas (W3C, 2004). These schemas are critical to the success of XML. They are used to ensure that an XML file adheres to a well-defined structure. Schemas are themselves XML files, which must conform to the XSD specification. Schema designers are free to develop constraints to varying degrees. Forcing an XML file to be compatible with a tightly-constrained schema frees developers from having to write their own data validation procedures. This leads to a great simplification of data manipulation software. 

W3C 2004. XML Schema Part 0 Primer Second Edition W3C Recommendation 28 October 2004... 

The W3C - the official owners of the XML and XML Schema recommendations - have a document describing a base set of use cases for evolution of XML Schemas (W3C 2006). The document does not provide any language or framework for mitigating such evolutions, but instead prescribes what the semantics and behavior should be for certain kinds of incremental schema evolution and how applications should behave when faced with the potential for data from multiple schema versions. For instance, Sect. 2.3 lists use cases where the same element in different versions of a schema contains different elements. Applications are instructed to ignore what they don t expect and be able to add extra elements without breaking the application. ... 

W3C (2006) XML schema versioning use cases. Framework for discussion of versioning, 2006. 

Each model format is defined using XML schema. XML Schema, pubhshed as a W3C recommendation, is one of several XML schema languages (W3C 2004). 

SAWSDL W3C Committee, 2007, SAWSDL (Semantic annotations for WSDL and XML schema). Available at http //www.w3.Org/TR/2007/REC-sawsdl-20070828/ Example... 

Introduction of XML formats was a very important step toward better intercomputer communication, but it is not a miraculous solution to all problems. Not every possible relation is easily expressed in XML (Wang et al. 2005), so specifications usually contain many implicit assumptions that are not properly formalized. The Resource Description Framework (RDF) provides a very powerful yet simple model for this formalization (Manola and Miller 2004). In this framework, any information is transformed to basic units called triplets that are combined to map the available information. This unifying mechanism can be used to express hierarchical vocabularies for domain knowledge description, as in RDF Schema (Brickley and Guha 2004) or its extension, Web Ontology Language (OWL) (Smith et al. 2004), both standardized by the W3C. 

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