Description Logics Emerge from Ivory Towers

Description logic (DL) has existed as a field for a few decades yet somewhat recently have appeared to transform from an area of academic interest to an area of broad interest. This paper provides a brief historical perspective of description logic developments that have impacted their usability beyond just in universities and research labs and provides one perspective on the topic. Description logics (previously called terminological logics and KL-ONE-like systems) started with a motivation of providing a formal foundation for semantic networks. The first implemented DL system – KL-ONE – grew out of Brachman’s thesis [Brachman, 1977]. This work was influenced by the work on frame systems but was focused on providing a foundation for building term meanings in a semantically meaningful and unambiguous manner. It rejected the notion of maintaining an ever growing (seemingly adhoc) vocabulary of link and node names seen in semantic networks and instead embraced the notion of a fixed set of domain-independent “epistemological primitives” that could be used to construct complex, structured object descriptions. It included constructs such as “defines-an-attribute-of” as a built-in construct and expected terms like “has-employee” to be higher-level terms built up from the epistemological primitives. Higher level terms such as “has-employee” and “has-part-time-employee” could be related automatically based on term definitions instead of requiring a user to place links between them. In its original incarnation, this led to maintaining the motivation of semantic networks of providing broad expressive capabilities (since people wanted to be able to represent natural language applications) coupled with the motivation of providing a foundation of building blocks that could be used in a principled and well-defined manner. KL-ONE provided an important first step in description logic history and since then, many systems have been designed and implemented taking differing positions on the requirements of expressive power, completeness of reasoning, and tractability of reasoning. One early paper describing some description logic systems up to 1990 is provided in [MacGregor, 1991] and includes some of the earlier implemented and used systems such as BACK [Peltason, 1991], CLASSIC [Brachman et al, 1989], and LOOM [MacGregor, 1991]. K-REP [Mays et al, 1991], although not included in that article, also appeared in the same time frame. Some of these early systems are interesting from the perspective of DLs emerging from ivory towers since one (BACK) made an attempt to be the basis of a company, another (K-REP) was the basis of a domain-specific commercial application in medical information systems which spun out of IBM, another (CLASSIC) was the basis of a family of some commercially fielded applications in the areas of data mining (IMACS [Selfridge-et-al, 1993]), knowledge-enhanced search (FindUR [McGuinness-et-al, 1998; McGuinness,2000]), and a family of configurators fielded at AT&T and Lucent that were deployed for over a decade(PROSE/QUESTAR[McGuinness-Wright, 2000]). Another (LOOM) was also was used extensively in a number of government research and application programs. Some of these (and other) early systems have had success moving from their roots in universities or industrial research labs into use in fielded (e.g. [Brachman et al, 1999], [Rychtyckyj, 1996]) applications and provide good examples of use in practice for the description logic-based applications of today.