Now, let’s finish up with RDF and OWL...my take.

Resource Description Framework (RDF), a part of the XML story, provides interoperability between applications that exchange information. RDF is another Web standard that's finding use everywhere, including SOA. RDF was developed by the W3C to provide a foundation of metadata interoperability across different resource description communities and is the basis for the W3C movement to ontologies such as the use of Web Ontology Language (OWL).

RDF uses XML to define a foundation for processing metadata and to provide a standard metadata infrastructure for both the Web and the enterprise. The difference between the two is that XML is used to transport data using a common format, while RDF is layered on top of XML defining a broad category of data. When the XML data is declared to be of the RDF format, applications are then able to understand the data without understanding who sent it.

RDF extends the XML model and syntax to be specified for describing either resources or a collection of information. (XML points to a resource in order to scope and uniquely identify a set of properties known as the schema.)

RDF metadata can be applied to many areas, including SOA. One example would be searching for data, and cataloging data and relationships. RDF is also able to support new technology (such as intelligent software agents and exchange of content rating).

RDF itself does not offer predefined vocabularies for authoring metadata. However, the W3C does expect standard vocabularies to emerge once the infrastructure for metadata interoperability is in place. Anyone, or any industry, can design and implement a new vocabulary. The only requirement is that all resources be included in the metadata instances using the new vocabulary.

RDF benefits SOA in that it supports the concept of a common metadata layer that is sharable throughout an enterprise or between enterprises. Thus, RDF can be used as a common mechanism for describing data within the SOA problem domain.

The Semantic Web is the abstract representation of data on the World Wide Web, based on the Resource Description Framework standards and other standards still to be defined. It is being developed by the W3C, in collaboration with a large number of researchers and industrial partners, lead by Tim Berners-Lee.

In order for the Semantic Web to function, computers must have access to structured collections of information and sets of inference rules that they can use to conduct automated reasoning. This notion is known as knowledge representation.

To this end, and in the domain of the World Wide Web, computers will find the meaning of semantic data by following hyperlinks to definitions of key terms and rules for logically reasoning about data. The resulting infrastructure will spur the development of automated Web services such as highly functional agents. What's important here is that the work now being driven by the W3C as a way to manage semantics on the Web is applicable, at least at the component level, to the world of SOA, much like XML and Web services.

An example of the W3C contribution to the use of ontologies is the Web Ontology Language. OWL is a semantic markup language for publishing and sharing ontologies on the World Wide Web. OWL is derived from the DAML+OIL Web Ontology Language and builds upon the RDF. OWL assigns a specific meaning to certain RDF triples. The future Formal Specification at the W3C, specifies exactly which triples are assigned a specific meaning, and offers a definition of the meaning. OWL only provides a semantic interpretation for those parts of an RDF graph that instantiate the schema. Any additional RDF statements resulting in additional RDF triples are allowed, but OWL is silent on the semantic consequences of such additional triples. An OWL ontology is made up of several components, some of which are optional, and some of which may be repeated.

Using these Web-based standards as the jumping-off point for ontology and SOA, it's possible to define and automate the use of ontologies in both intra- and intercompany SOA domains. Domains made up of thousands of systems, all with their own semantic meanings, bound together in a common ontology that makes short work of SOA and defines a common semantic meaning of data. This, indeed, is the goal.

Extending from the languages, we have several libraries available for a variety of vertical domains, including financial services and e-Business. We also have many knowledge editors that now exist to support the creation of ontologies, as well as the use of natural-language processing methodologies.

In other words, we have a standards set of tools to define, manage, and share application semantics from domain to domain, including from the enterprise to the Internet, and back. It's time we started to use them.

Posted by Dave Linthicum on November 16, 2006 05:53 AM