Showing papers by "Giuseppe De Giacomo published in 2001"

A framework for ontology integration

Abstract: One of the basic problems in the development of techniques for the semantic web is the integration of ontologies. Indeed, the web is constituted by a variety of information sources, each expressed over a certain ontology, and in order to extract information from such sources, their semantic integration and reconciliation in terms of a global ontology is required. In this paper, we address the fundamental problem of how to specify the mapping between the global ontology and the local ontologies. We argue that for capturing such mapping in an appropriate way, the notion of query is a crucial one, since it is very likely that a concept in one ontology corresponds to a view (i.e., a query) over the other ontologies. As a result query processing in ontology integration systems is strongly related to view-based query answering in data integration.

Data integration in data warehousing

Abstract: Information integration is one of the most important aspects of a Data Warehouse. When data passes from the sources of the application-oriented operational environment to the Data Warehouse, possible inconsistencies and redundancies should be resolved, so that the warehouse is able to provide an integrated and reconciled view of data of the organization. We describe a novel approach to data integration in Data Warehousing. Our approach is based on a conceptual representation of the Data Warehouse application domain, and follows the so-called local-as-view paradigm: both source and Data Warehouse relations are defined as views over the conceptual model. We propose a technique for declaratively specifying suitable reconciliation correspondences to be used in order to solve conflicts among data in different sources. The main goal of the method is to support the design of mediators that materialize the data in the Data Warehouse relations. Starting from the specification of one such relation as a query over the conceptual model, a rewriting algorithm reformulates the query in terms of both the source relations and the reconciliation correspondences, thus obtaining a correct specification of how to load the data in the materialized view.

Identification constraints and functional dependencies in description logics

Abstract: DLR is an expressive Description Logic (DL) with n-ary relations, particularly suited for modeling database schemas. Although DLR has constituted one of the crucial steps for applying DL technology to data management, there is one important aspect of database schemas that DLs, including DLR, do not capture yet, namely the notion of identification constraints and functional dependencies. In this paper we introduce a DL which extends DLR and fully captures the semantics of such constraints, and we address the problem of reasoning in such a logic. We show that, verifying knowledge base satisfiability and logical implication in the presence of identification constraints and nonunary functional dependencies can be done in EXPTIME, thus with the same worst-case computational complexity as for plain DLR. We also show that adding just unary functional dependencies to DLR leads to undecidability.

Ontology of Integration and Integration of Ontologies.

Abstract: One of the basic problems in the development of techniques for the semantic web is the integration of ontologies. In this paper we deal with a situation where we have various local ontologies, developed independently from each other, and we are required to build an integrated, global ontology as a mean for extracting information from the local ones. In this context, the problem of how to specify the mapping between the global ontology and the local ontologies is a fundamental one, and its solution is essential for establishing an ontology of integration. Description Logics (DLs) are an ideal candidate to formalize ontologies, due to their ability to express complex relationships between concepts. We argue, however, that, for capturing the mapping between different ontologies, the direct use of a DL, even a very expressive one, is not sufficient, and it is necessary to resort to more flexible mechanisms based on the notion of query. Also, we elaborate on the observation that, in the semantic web, the case of mutually inconsistent local ontologies will be very common, and we present the basic ideas in order to extend the integration framework with suitable nonmonotonic features for dealing with this case.

Accessing Data Integration Systems through Conceptual Schemas

Abstract: Data integration systems provide access to a set of heterogeneous, autonomous data sources through a so-called global, or mediated view. There is a general consensus that the best way to describe the global view is through a conceptual data model, and that there are basically two approaches for designing a data integration system. In the global-as-view approach, one defines the concepts in the global schema as views over the sources, whereas in the local-as-view approach, one characterizes the sources as views over the global schema. It is well known that processing queries in the latter approach is similar to query answering with incomplete information, and, therefore, is a complex task. On the other hand, it is a common opinion that query processing is much easier in the former approach. In this paper we show the surprising result that, when the global schema is expressed in terms of a conceptual data model, even a very simple one, query processing becomes difficult in the global-as-view approach also. We demonstrate that the problem of incomplete information arises in this case too, and we illustrate some basic techniques for effectively answering queries posed to the global schema of the data integration system.

Reasoning on UML Class Diagrams using Description Logic Based Systems

Abstract: Recently, a growing interest in description logics and their applications can be observed. This is mainly due to the development of very expressive description logics and optimized description logic systems which support terminological and/or assertional reasoning for these logics. This workshop intended to gather researchers as well as practitioners who are interested in description logics and their applications. The primary focus of this workshop was on applications of description logics. Ian Horrocks, University of Manchester, gives a tutorial-style talk about latest developments in description logic research. These proceedings can also be found at http://www.CEUR-WS.org.

View-Based Query Answering and Query Containment over Semistructured Data

Abstract: The basic querying mechanism over semistructured data, namely regular path queries, asks for all pairs of objects that are connected by a path conforming to a regular expression. We consider conjunctive two-way regular path queries (C2RPQc's), which extend regular path queries with two features. First, they add the inverse operator, which allows for expressing navigations in the database that traverse the edges both backward and forward. Second, they allow for using conjunctions of atoms, where each atom specifies that a regular path query with inverse holds between two terms, where each term is either a variable or a constant. For such queries we address the problem of view-based query answering, which amounts to computing the result of a query only on the basis of a set of views. More specifically, we present the following results: (1) We exhibit a mutual reduction between query containment and the recognition problem for view-based query answering for C2RPQc's, i.e., checking whether a given tuple is in the certain answer to a query. Based on such a result, we can show that the problem of view-based query answering for C2RPQc's is EXPSPACE-complete. (2) By exploiting techniques based on alternating two-way automata we show that for the restricted class of tree two-way regular path queries (in which the links between variables form a tree), query containment and view-based query answering are, rather surprisingly, in PSPACE (and hence, PSPACE-complete). (3) We present a technique to obtain view-based query answering algorithms that compute the whole set of tuples in the certain answer, instead of requiring to check each tuple separately. The technique is parametric wrt the query language, and can be applied both to C2RPQc's and to tree-queries.

Incremental execution of guarded theories

Abstract: When it comes to building controllers for robots or agents, high level programming languages like Golog and ConGolog offer a useful compromise between planning-based approaches and low-level robot programming. However, two serious problems typically emerge in practical implementations of these languages: how to evaluate test in a program efficiently enough in an open-world setting, and how to make appropiate nondeterministic choices while avoiding full lookahead. Recent proposals in the literature suggest that one could tackle the first problem by exploiting sensing information, and tackle the second by specifying the amount of lookahead allowed explicitly in the program. In this paper, we combine these two ideas and demonstrate their power by presenting an interpreter, written in Prolog, for a variant of Golog that is suitable for efficiently operating in open-world setting by exploiting sensing and bounded lookahead.

Description Logic Formalization of CIM

Abstract: Common Information Model (CIM) has the goal of providing a suitable approach for modeling systems and networks using the object-oriented paradigm In this document we illustrate how to map CIM onto an expressive Description Logics, called DLRifd, so as to obtain a rigorous logical framework for representing and reasoning on managed systems The document is organized as follows We first give an overview of both CIM and the Description Logic DLRifd We then illustrate the formalization of CIM in terms of DLRifd Finally, we present an example of how such a formalization works, by showing how the CIM Core model and the CIM Common model is expressed in DLRifd