Frames and OWL Side by Side

Understanding the relation of the two most widely-used ontology modeling paradigms, OWL (and other DL paradigm) to frame paradigms is an important issue. Because the Protege tool supports both paradigms within a single overall framework, it provides an opportunity to compare the two paradigms both in theory and practice. In this paper, we focus on the relationship between the Frames paradigm, as defined in the OKBC specification 1 and implemented in core Protege, and OWL and its implementation in Protege-OWL. OWL provides three increasingly expressive sublanguages, OWL Lite, OWL DL, and OWL Full, for different communities of users. In this paper, we will primarily use OWL DL as the basis for comparison, as OWL DL provides the description-logic reasoning capabilities that are the distinctive features of OWL. Therefore, unless otherwise noted, when we use “OWL”, we are actually referring to OWL DL. Contrastingly, there is not a single standard frame representation language analogous to OWL. The past standardization effort has produced the Open Knowledge-Base Connectivity (OKBC) protocol, which is a generic access and manipulation layer for knowledge representation services. For the purpose of this paper, we will primarily use the Protege-Frames implementation of the OKBC Knowledge Model. When appropriate, we comment on features of frame representations that may not be available in Protege. Unless otherwise noted, when we use “Frames,” we are actually referring to Protege-Frames.