Abstract:
The representation of temporal information has been in the center of intensive research activities over the years in
the areas of knowledge representation, databases and more recently, the Semantic Web. The proposed approach extends the
existing framework of representing temporal information in ontologies by allowing for representation of concepts evolving in
time (referred to as “dynamic” information) and of their properties in terms of qualitative descriptions in addition to quantitative
ones (i.e., dates, time instants and intervals). For this purpose, we advocate the use of natural language expressions, such as
“before” or “after”, for temporal entities whose exact durations or starting and ending points in time are unknown. Reasoning
over all types of temporal information (such as the above) is also an important research problem. The current work addresses all
these issues as follows: The representation of dynamic concepts is achieved using the “4D-fluents” or, alternatively, the “N-ary
relations” mechanism. Both mechanisms are thoroughly explored and are expanded for representing qualitative and quantitative
temporal information in OWL. In turn, temporal information is expressed using either intervals or time instants. Qualitative
temporal information representation in particular, is realized using sets of SWRL rules and OWL axioms leading to a sound,
complete and tractable reasoning procedure based on path consistency applied on the existing relation sets. Building upon existing
Semantic Web standards (OWL), tools and member submissions (SWRL), as well as integrating temporal reasoning support into
the proposed representation, are important design features of our approach.