In this paper a semantic approach for the specification and the management of databases with evolving schemata is introduced. It is shown how a general object-oriented model for schema versioning and evolution can be formalized; how the semantics of schema change operations can be defined; how interesting reasoning tasks can be supported, based on an encoding in description logics.

Recent efforts in the Conceptual Modelling community have been devoted to properly capturing time-varying information. Various temporally enhanced Entity-Relationship (ER) models have been proposed that are intended to model the temporal aspects of database conceptual schemas. This work gives a logical formalisation of the various properties that characterise and extend different temporal ER models which are found in literature. The formalisation we propose is based on Description Logics (DL), which have been proved useful for a logical reconstruction of the most popular conceptual data modelling formalisms.

This paper introduces a new logical formalism, intended for temporal conceptual modelling, as a natural combination of the well-known description logic DLR and point-based linear temporal logic with Since and Until. The expressive power of the resulting DLRUS logic is illustrated by providing a characterisation of the most important temporal conceptual modelling constructs appeared in the literature. We define a query language (where queries are non-recursive Datalog programs and atoms are complex DLRUS expressions) and investigate the problem of checking query containment under the constraints defined by DLRUS conceptual schemas---i.e., DLRUS knowledge bases---as well as the problems of schema satisfiability and logical implication.

Abstract not found

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. DLRUS, the description logic DLR extended with the temporal operators Since and Until. We show how DLRUS is able to capture the various modelling constraints in a succinct way and to perform automated reasoning on temporal conceptual models.

Abstract. The trend towards pervasive computing is driving a need for applications that are highly autonomous, as well as responsive to changes in their environments and in user requirements. Such applications are commonly termed context-aware, and are reliant on accurate information about aspects of their surroundings such as the location, goals and activities of users. Unfortunately, the construction of context-aware applications is a difficult task, and, for this reason, various infrastructures supporting the construction of such applications by assisting with the gathering, processing and dissemination of context information have re-cently appeared [1-3]. However, these are based on models of context that lack formality and expressiveness and offer little support for the design tasks associated with context-aware applications. In this paper, we present a context modelling approach that offers a means for developers to describe and program with context at a high level, without the need to consider issues related to context gathering, management or representation. We also describe a mapping process that transforms high-level context models to management systems capable of maintaining and supplying context information to applications at run-time.

Advanced personalized web applications require a carefully dealing with their users ’ wishes and preferences. Since such preferences do not always hold in general, personalized applications also have to consider the user’s current situation. In this paper we present a novel framework for modeling situations and situated preferences. Our approach consists of a general meta model for situations, which can be applied as foundation for situation models in a wide range of applications. Furthermore, an XML-based preference repository for the storage and management of situated preferences is developed. Long-term and situated preferences can easily be accessed with the preference repository interface. Particularly, preferences best-matching to a given situation can be queried. This approach allows web applications to react flexibly and personalized to the changing situations of their users.

In the first part of this Chapter we will introduce a general temporally enhanced conceptual data model able to represent time varying data, in the spirit of a temporally enhanced Entity-Relationship data model. In the second part, we will introduce an object-oriented conceptual data model enriched with schema change operators, which are able to represent the explicit temporal evolution of the schema while maintaining a consistent view on the (static) instantiated data. We will introduce a provably correct encoding of both conceptual data models and their inference problems in Description Logics. In this way, we study the properties of both the temporal conceptual data model and the object-oriented data model with schema change facilities.

In this paper a semantic approach for the specification and the management of databases with evolving schemata is introduced. It is shown how a general objectoriented model for schema versioning and evolution can be formalised; how the semantics of schema change operations can be defined; how interesting reasoning tasks can be supported, based on an encoding in Description Logics.

Past research work on modelling and managing temporal information has, so far, failed to elicit support in commercial database systems. The increasing popularity of XML and XQuery offers a unique opportunity to change this situation, inasmuch as these support temporal information much better than relational tables and SQL. This is the important conclusion claimed in this paper where we show that valid-time, transaction-time, and bitemporal databases can be naturally viewed in XML using temporally-grouped data models; then we show that complex historical queries, that would be very di#cult to express in SQL on relational tables, can now be easily expressed in standard XQuery on such XML-based representations. We first discuss the management of transaction-time and valid-time histories and then extend our approach to bitemporal histories. The approach can be generalized naturally to support the temporal management of arbitrary XML documents and queries on their version history.