Reading notes for Lecture 14

The main idea of the semantic web is machine-readable ontology standards. An "ontology" is a theory of the categories of things that comprise a given domain. Familiar examples of ontologies include taxonomies and controlled vocabularies. Every computer system uses an ontology. Computer systems that are built independently of one another, however, often cannot interoperate because they use different ontologies. Now that computer systems are heavily networked, numerous user groups have begun standardizing their ontologies. The semantic web consists of mechanisms for "marking up" ontologies and then processing them.
There are roughly four kinds of ontologies: document ontologies (e.g., the chapters of a book or the footnotes of a paper), metadata ontologies (e.g., the format of a file or the copyright status of a document), domain ontologies (e.g., the components of an automobile or the entries of a schedule), and service ontologies (e.g., the inputs of a software module, the steps of a transaction, or the formats of messages that are passed back and forth between a client and server). Because its topic is information retrieval and not web services generally, this course is mainly about document and metadata ontologies. In practice, however, document and metadata ontologies often include elements of domain ontologies, and many services use documents and metadata. For completeness, therefore, weeks 9 and 10 respectively will be on domain and service ontologies.
The semantic web includes a layered series of markup languages starting with XML (itself derived from SGML). The most distinctive aspect of XML is that user groups can use it to define specialized sublanguages to mark up the ontologies that are meaningful for their own work. "User-centered design" in a semantic web context means precisely the codification of a user group's ontologies. This is important because document collections that have been marked up within a standard XML-based language can be stored and retrieved in much more sophisticated ways than unstructured plain text documents, or documents whose structures have not been marked up in a standardized way. Although it is too soon to be certain, the result may be a revolution in the technology of information retrieval. In the past, this course has generally applied ideas from user interface design to more traditional information retrieval technologies.