188,478 research outputs found
Testing Termination of Query Satisfiability Checking on Expressive Database Schemas
A query is satisfiable if there is at least one consistent instance of the database in which it has a non-empty answer. Defining queries on a database schema and checking their satisfiability can help the database designer to be sure whether the produced database schema is what was intended. The formulation of such queries may easily require the use of some arithmetic comparisons or negated expressions. Unfortunately, checking the satisfiability of this class of queries on a database schema that most likely have some
integrity constraints (e.g., keys, foreign keys, Boolean checks) is, in general, undecidable.
However, although the problem is undecidable for such a class of schemas and queries, it
may not be so for a particular query satisfiability check. In this paper, we propose to perform a termination test as a previous step to query satisfiability checking. If positive, the termination test guarantees that the corresponding query satisfiability check will terminate. We assume the CQC method is the underlying query satisfiability checking method; to the best of our knowledge, it is the only method of this kind able to deal with schemas and queries as expressive as the ones we consider.Preprin
Output constraints in multimedia database systems
Zusammenfassung
Semantische Fehler treten bei jeder Art von Datenverwaltung auf. Herkömmliche
Datenbanksysteme verwenden eine Integritätskontrolle, um semantische Fehler zu
vermeiden. Um die Integrität der Daten zu gewährleisten werden Integritätsregeln
benutzt. Diese Regeln können allerdings nur die Konsistenz einfach
strukturierter Daten überprüfen.
Multimedia Datenbanksystem verwalten neben einfachen alphanumerischen Daten auch
komplexe Mediendaten wie Videos. Um die Konsistenz dieser Daten zu sichern,
bedarf es einer erheblichen Erweiterung des bestehenden Integritätskonzeptes.
Dabei muss besonders auf die konsistente Datenausgabe geachtet werden. Im
Gegensatz zu alphanumerischen Daten können Mediendaten während der Ausgabe
verfälscht werden. Dieser Fall kann eintreten, wenn eine geforderte
Datenqualität bei der Ausgabe nicht erreicht werden kann oder wenn
Synchronisationsbedingungen
zwischen Medienobjekten nicht eingehalten werden können. Es besteht daher die
Notwendigkeit, Ouptut Constraints einzuführen. Mit ihrer Hilfe kann definiert
werden, wann die Ausgabe von Mediendaten semantisch korrekt ist. Das
Datenbanksystem kann diese Bedingungen überprüfen und so gewährleisten, dass der
Nutzer semantisch einwandfreie Daten erhält.
In dieser Arbeit werden alle Aspekte betrachtet, die notwendig sind, um
Ausgabebedingungen in ein Multimedia Datenbanksystem zu integrieren. Im
einzelnen werden die Modellierung der Bedingungen, deren datenbankinterne
Repräsentation sowie die Bedingungsüberprüfung betrachtet.
Für die Bedingungsmodellierung wird eine Constraint Language auf Basis der
Prädikatenlogik eingeführt. Um die Definition von zeitlichen und räumlichen
Synchronisationen zu ermöglichen, verwenden wir Allen-Relationen. Für die
effiziente Überprüfung der Ausgabebedingungen müssen diese aus der
Spezifikationssprache in eine datenbankinterne Darstellung überführt werden.
Für die datenbankinterne Darstellung werden Difference Constraints verwendet.
Diese erlauben eine sehr effiziente Bedingungsüberprüfung. Wir haben Algorithmen
entwickelt, die eine effiziente Überprüfung von Ausgabebedingungen erlauben und
dies anhand von Experimenten nachgewiesen. Neben der Überprüfung der Bedingungen
müssen Mediendaten so synchronisiert werden, dass dies den Ausgabebedingungen
entspricht. Wir haben dazu das Konzept des Output Schedules entwickelt. Dieser
wird aufgrund der definierten Ausgabebedingungen generiert.
Durch die Ausgabebedingungen, die in dieser Arbeit eingeführt werden, werden
semantische Fehler bei der Verwaltung von Mediendaten erheblich reduziert. Die
Arbeit stellt daher einen Beitrag zur qualitativen Verbesserung der Verwaltung
von Mediendaten dar.Semantic errors exist as long as data are managed. Traditional database systems try to prevent this errors by proposing integrity
concepts for stored data. Integrity constraints are used to implement these integrity concepts. However, integrity constraints can only detect semantic errors in elementary data.
Multimedia database systems manage elementary data as well as complex media data, like videos. Considering these media data we need a much wider consistency concept as traditional database systems provide. Especially, data output of media data must be taken into account. In contrast to alphanumeric data the semantics of media data can be falsified during data output if data quality or
synchronization of data are not suitable. Thus, we need a concept for output constraints that allow for preventing semantic errors in case of data output. For integrating output constraints into a multimedia database system we have to consider modelling, representation and checking of output constraints.
For modelling output constraints we have introduced a constraint language which uses the same principles as traditional constraint languages. Our constraint specification language must support temporal and spatial synchronization constraints. However, it is desired to support both kinds of synchronization in almost the same manner. Therefore, we use Allen-Relations for defining temporal
synchronization constraints as well as for defining spatial synchronization constraints.
We need a database internal representation of output constraints that makes efficient constraint checking possible. The Allen-Relations used in the constraint language cannot be checked efficiently. However, difference constraints are a class of constraints that allows an very efficient checking. Therefore, we use difference constraints as database internal representation of output constraints.
As methods for checking consistency of output constraints we use an approach based on graph theory as well as an analytical approach. Both approaches require a constraint graph as data structure. For data output we need an output order that is adequate to the defined output constraints. This output schedule can be produced based on the output constraints.
With output constraints, proposed in this thesis, semantical correctness of media data considering the data output can be supported.Thus, the contribution of this work is an qualitative improvement of managing media data by database systems
Using formal metamodels to check consistency of functional views in information systems specification
UML notations require adaptation for applications such as Information Systems (IS). Thus we have defined IS-UML. The purpose of this article is twofold. First, we propose an extension to this language to deal with functional aspects of IS. We use two views to specify IS transactions: the first one is defined as a combination of behavioural UML diagrams (collaboration and state diagrams), and the second one is based on the definition of specific classes of an extended class diagram. The final objective of the article is to consider consistency issues between the various diagrams of an IS-UML specification. In common with other UML languages, we use a metamodel to define IS-UML. We use class diagrams to summarize the metamodel structure and a formal language, B, for the full metamodel. This allows us to formally express consistency checks and mapping rules between specific metamodel concepts. (C) 2007 Elsevier B.V. All rights reserved
Integrity Constraints in Trust Management
We introduce the use, monitoring, and enforcement of integrity constraints in
trust management-style authorization systems. We consider what portions of the
policy state must be monitored to detect violations of integrity constraints.
Then we address the fact that not all participants in a trust management system
can be trusted to assist in such monitoring, and show how many integrity
constraints can be monitored in a conservative manner so that trusted
participants detect and report if the system enters a policy state from which
evolution in unmonitored portions of the policy could lead to a constraint
violation.Comment: An extended abstract appears in the proc. of the 10th ACM Symp. on
Access Control Models and Technologies (SACMAT). 200
The Constructive method for query containment checking (extended version)
We present a new method that checks Query Containment for queries with negated derived atoms and/or integrity constraints.
Existing methods for Query Containment checking that deal with these cases do not check actually containment but another
related property called uniform containment, which is a sufficient but not necessary condition for containment. Our method can
be seen as an extension of the canonical databases approach beyond the class of conjunctive queries.Postprint (published version
The CIFF Proof Procedure for Abductive Logic Programming with Constraints: Theory, Implementation and Experiments
We present the CIFF proof procedure for abductive logic programming with
constraints, and we prove its correctness. CIFF is an extension of the IFF
proof procedure for abductive logic programming, relaxing the original
restrictions over variable quantification (allowedness conditions) and
incorporating a constraint solver to deal with numerical constraints as in
constraint logic programming. Finally, we describe the CIFF system, comparing
it with state of the art abductive systems and answer set solvers and showing
how to use it to program some applications. (To appear in Theory and Practice
of Logic Programming - TPLP)
LCM and MCM: specification of a control system using dynamic logic and process algebra
LCM 3.0 is a specification language based on dynamic logic and process algebra, and can be used to specify systems of dynamic objects that communicate synchronously. LCM 3.0 was developed for the specification of object-oriented information systems, but contains sufficient facilities for the specification of control to apply it to the specification of control-intensive systems as well. In this paper, the results of such an application are reported. The paper concludes with a discussion of the need for theorem-proving support and of the extensions that would be needed to be able to specify real-time properties
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