Alessandro Artale

Part-whole relations in object-centered systems: an overview

Abstract Knowledge bases, data bases and object-oriented systems (referred to in the paper as Object-Centered systems) all rely on attributes as the main construct used to associate properties to objects; among these, a fundamental role is played by the so-called part-whole relation. The representation of such structural information usually requires particular semantics together with specialized inference and update mechanisms, but rarely do current modelling formalisms and methodologies give it a specific, ‘first-class’ dignity. The main thesis of this paper is that the part-whole relation cannot simply be considered as an ordinary attribute: its specific ontological nature requires to be understood and integrated within data-modelling formalisms and methodologies. On the basis of such an ontological perspective, we survey the conceptual modelling issues involving part-whole relations, and the various modelling frameworks provided by knowledge representation and object-oriented formalisms.

A survey of temporal extensions of description logics

This paper surveys the temporal extensions of description logics appearearing in the literature. The analysis considers a large spectrum of approaches appearearing in the temporal description logics area: from the loosely coupled approaches – which comprise, for example, the enhancement of simple description logics with a constraint based mechanism – to the most principled ones – which consider a combined semantics for the abstract and the temporal domains. It will be shown how these latter approaches have a strict connection with temporal logics.Advantages of using temporal description logics are their high expressivity combined with desirable computational properties – such as decidability, soundness and completeness of deduction procedures. In this survey the computational properties of various families of temporal description logics will be pointed out.

A temporal description logic for reasoning about actions and plans

A class of interval-based temporal languages for uniformly representing and reasoning about actions and plans is presented. Actions are represented by describing what is true while the action itself is occurring, and plans are constructed by temporally relating actions and world states. The temporal languages are members of the family of Description Logics, which are characterized by high expressivity combined with good computational properties. The subsumption problem for a class of temporal Description Logics is investigated and sound and complete decision procedures are given. The basic language TL-F is considered first: it is the composition of a temporal logic TL - able to express interval temporal networks - together with the non-temporal logic F - a Feature Description Logic. It is proven that subsumption in this language is an NP-complete problem. Then it is shown how to reason with the more expressive languages TLU-FU and TL-ALCF. The former adds disjunction both at the temporal and non-temporal sides of the language, the latter extends the non-temporal side with set-valued features (i.e., roles) and a propositionally complete language.

Representing and reasoning over a taxonomy of part-whole relations

Many types of part-whole relations have been proposed in the literature to aid the conceptual modeller to choose the most appropriate type, but many of those relations lack a formal specification to give clear and unambiguous semantics to them. To remedy this, a formal taxonomy of types of mereological and meronymic part-whole relations is presented that distinguishes between transitive and intransitive relations and the kind of entity types that are related. The demand to use it effectively brings afore new requirements for automated reasoning over a hierarchy of relations. To ensure logically and ontologically correct inferencing over both the class and role hierarchy, the new reasoning service RBox compatibility for Description Logics reasoners is introduced. The proposed combination of formal semantics and the new reasoning service will improve the representation of the application domain when using part-whole relations in conceptual models and ontologies.

Reasoning over extended ER models

We investigate the computational complexity of reasoning over various fragments of the Extended Entity-Relationship (EER) language, which includes a number of constructs: ISA between entities and relationships, disjointness and covering of entities and relationships, cardinality constraints for entities in relationships and their refinements as well as multiplicity constraints for attributes. We extend the known EXPTIME-completeness result for UML class diagrams [5] and show that reasoning over EER diagrams with ISA between relationships is EXPTIME-complete even without relationship covering. Surprisingly, reasoning becomes NP-complete when we drop ISA between relationships (while still allowing all types of constraints on entities). If we further omit disjointness and covering over entities, reasoning becomes polynomial. Our lower complexity bound results are proved by direct reductions, while the upper bounds follow from the correspondences with expressive variants of the description logic DL-Lite, which we establish in this paper. These correspondences also show the usefulness of DL-Lite as a language for reasoning over conceptual models and ontologies.

Temporal Description Logics.

This chapter will survey the temporal extensions of Description Logics. These formalisms give an emphasis to reasoning tasks such as satis ability, subsumption, classi cation, and instance recognition. The analysis will include the whole spectrum of approaches used within the Temporal Description Logics area: from the loosely coupled approaches { which comprise, for example, the enhancement of simple Description Logics with a constraint based mechanism { to the most principled ones { considering a combined semantics for the abstract and the temporal domains. We wil show how these latter approaches described shares many similarities with approaches based on modal temporal logics, since Description Logics share many features with modal logic.

OCL-Lite: Finite reasoning on UML/OCL conceptual schemas

To ensure the quality of an information system we must guarantee the correctness of the conceptual schema that represents the knowledge about its domain. The high expressivity of UML schemas annotated with textual OCL constraints enforces the need for automated reasoning techniques. These techniques should be both terminating and complete to be effectively used in practice. In this paper we identify an expressive fragment of the OCL language that ensures these properties. In this way, we overcome the limitations of current techniques when reasoning on such a fragment. As a consequence, we also have that Description Logics can be appropriately used to reason on UML conceptual schemas with arbitrary OCL constraints. We also show how current tools based on different approaches can be used to reason on conceptual schemas enriched with (a decidable fragment of) OCL constraints.

Evolving objects in temporal information systems

This paper presents a semantic foundation of temporal conceptual models used to design temporal information systems. We consider a modelling language able to express both timestamping and evolution constraints. We conduct a deeper investigation of evolution constraints, eventually devising a model-theoretic semantics for a full-fledged model with both timestamping and evolution constraints. The proposed formalization is meant both to clarify the meaning of the various temporal constructors that appeared in the literature and to give a rigorous definition, in the context of temporal information systems, to notions like satisfiability, subsumption and logical implication. Furthermore, we show how to express temporal constraints using a subset of first-order temporal logic, i.e.,

Temporal ER Modeling with Description Logics

\mathcal{DLR}{_{\mathcal{US}}}

A Temporal Description Logic for Reasoning over Conceptual Schemas and Queries

the description logic