Temporal Extensions to RDF

Abstract

The Semantic Web aims at building a foundation of semantic-based data models and languages for not only manipulating data and knowledge, but also in decision making by machines. Naturally, time-varying data and knowledge are required in Semantic Web applications to incorporate time and further reason about it. However, the original specifications of RDF and OWL do not include constructs for handling time-varying data and knowledge. For simplicity, RDF model is confined to binary predicates, hence some form of reification is needed to represent higher-arity predicates. To this date, there are many proposals extending RDF and OWL for handling temporal data and knowledge. They all focus on the valid time. In this paper, we examine each of these proposals and develop a taxonomy to classify them according to the form of reification employed: explicit reification or implicit reification. The implicit reification proposals are further divided into three sub-categories according to semantic constructs 126 Hsien-Tseng Wang and Abdullah Uz Tansel they use. Some of these proposals stay compliant to the RDF and OWL standards whereas others add new constructs to RDF model and SPARQL query language. Additionally, we compare these proposed models with respect to characteristics, such as their syntax and semantics, their compliance to RDF and OWL specifications, their need for additional objects, etc. The comparison provides a useful guideline for the researchers and practitioners of the Semantic Web in managing temporal data and knowledge.

Engineering uncertain time for its practical integration in ontologies

“…Differently from the approaches in Section 3.4, TimeOnto does not create new operators but creates temporal object properties that relate ontological concepts. For example, the Allen's relation Before may be generalised in three uncertain relations, where Before(1) means approximately the same time; Before (2) means just before and Before(3) means long before. Thus, this approach is focused on the qualification of uncertainty about the temporal distance of events, instead of the uncertainty about the existence of temporal relations.…”

“…This problem happens because ontologies use the Description Logics (DL) [1] as their formal basis, which is a decidable fragment of the first-order logic that only uses unary (concepts) and binary (roles) predicates. Therefore, ontologies do not naturally support representations for inputs such as "I slept well from 23:00 to J o u r n a l P r e -p r o o f Journal Pre-proof 04:00", "I had a posttraumatic stress disorder after my car accident", and "I had a heart attack in 1999"; while the current temporal extensions that are still compatible with the current ontology resources (e.g., reasoners and DL formalism) are limited in aspects related to uncertain time, the evolution of events, and relations between time concepts [2]. This lack of expressive and standards-compatible temporal representations restricts the range of reasoning processes because several time aspects, which are usually embedded in knowledge domains (e.g., health and education) [3], cannot be employed.…”