14 research outputs found
ON PERIODICITY IN TEMPORAL DATABASES
The issue of periodicity is generally understood to be a desirable property of temporal
data that should be supported by temporal database models and their query
languages. Nevertheless, there has so far not been any systematic examination of how
to incorporate this concept into a temporal DBMS. In this paper we describe two concepts
of periodicity, which we call strong periodicity and near periodicity, and discuss
how they capture formally two of the intuitive meanings of this term. We formally
compare the expressive power of these two concepts, relate them to existing temporal
query languages, and show how they can be incorporated into temporal relational
database query languages, such as the proposed temporal extension to SQL, in a clean
and straightforward manner.Information Systems Working Papers Serie
An efficient algorithm for minimizing time granularity periodical representations
This paper addresses the technical problem of efficiently reducing the periodic representation of a time granularity to its minimal form. The minimization algorithm presented in the paper has an immediate practical application: it allows users to intuitively define granularities (and more generally, recurring events) with algebraic expressions that are then internally translated to mathematical characterizations in terms of minimal periodic sets. Minimality plays a crucial role, since the value of the recurring period has been shown to dominate the complexity when processing periodic sets.
Temporal Data Modeling and Reasoning for Information Systems
Temporal knowledge representation and reasoning is a major research field in Artificial
Intelligence, in Database Systems, and in Web and Semantic Web research. The ability to
model and process time and calendar data is essential for many applications like appointment
scheduling, planning, Web services, temporal and active database systems, adaptive
Web applications, and mobile computing applications. This article aims at three complementary
goals. First, to provide with a general background in temporal data modeling
and reasoning approaches. Second, to serve as an orientation guide for further specific
reading. Third, to point to new application fields and research perspectives on temporal
knowledge representation and reasoning in the Web and Semantic Web
Irregular Indeterminate Repeated Facts in Temporal Relational Databases
Time is pervasive of reality, and many relational database approaches have been developed to cope with it. In
practical applications, facts can repeat several times, and only the overall period of time containing all the repetitions may be
known (consider, e.g., On January, John attended five meetings of the Bioinformatics project). While some temporal relational
databases have faced facts repeated at (known) periodic time, or single facts occurred at temporally indeterminate time, the
conjunction of non-periodic repetitions and temporal indeterminacy has not been faced yet. Coping with this problem requires
an in-depth extension of current techniques. In this paper, we have introduced a new data model, and new definitions of
relational algebraic operators coping with the above issues. We have studied the properties of the new model and algebra (with
emphasis on the reducibility property), and how it can be integrated with other models in the literature
An ontology design pattern for representing recurrent situations
In this Chapter, we present an Ontology Design Pattern for representing situations that recur at regular periods and share some invariant factors, which unify them conceptually: we refer to this set of recurring situations as recurrent situation series. The proposed pattern appears to be foundational, since it can be generalised for modelling the top-level domain-independent concept of recurrence, which is strictly associated with invariance. The pattern reuses other foundational patterns such as Collection, Description and Situation, Classification, Sequence. Indeed, a recurrent situation series is formalised as both a collection of situations occurring regularly over time and unified according to some properties that are common to all the members, and a situation itself, which provides a relational context to its members that satisfy a reference description. Besides including some exemplifying instances of this pattern, we show how it has been implemented and specialised to model recurrent cultural events and ceremonies in ArCo, the Knowledge Graph of Italian cultural heritage
Nearly Periodic Facts in Temporal Relational Databases
Despite the huge amount of work devoted to the treatment of time within the relational context, few relevant
temporal phenomena still remain to be addressed. One of them is the treatment of \u201cnearly periodic events\u201d, i.e., eventsacts
that occur in intervals of time which repeat periodically (e.g., a meeting occurring twice each Monday, possibly not at regular
times). Nearly periodic events are quite frequent in everyday life, and thus in many applicative contexts. Their treatment within
the relational model is quite challenging, since it involves the integrated treatment of three aspects: (i) the number of repetitions,
(ii) their periodicity, and (iii) temporal indeterminacy. Coping with this problem requires an in-depth extension of current temporal
relational database techniques. In this paper, we introduce a new data model, and new definitions of relational algebraic
operators coping with the above issues. We ascertain the properties of the new model and algebra, with emphasis on the
expressiveness of our representation model, on the reducibility property, and on the correctness of the algebraic operators
Dynamic context adaptation in multimedia documents
ABSTRACT Multimedia documents are collections of media objects, synchronized by means of sets of temporal and spatial constraints. Any multimedia document definition is valid as long as the referred media objects are available and the constraints are satisfiable. Document validity depends on the context in which the document has to be presented. In this paper, we introduce a framework to characterize context adaptation, in the presence of both physical and user oriented context requirements. We define semantically equivalent presentation fragments as alternative to undeliverable ones. In the absence of equivalence, undeliverable media are replaced with candidates that minimize the loss of information/quality in the presentation