Sonia Bergamaschi

Semantic integration of semistructured and structured data sources

Providing an integrated access to multiple heterogeneous sources is a challenging issue in global information systems for cooperation and interoperability. In this context, two fundamental problems arise. First, how to determine if the sources contain semantically related information, that is, information related to the same or similar real-world concept(s). Second, how to handle semantic heterogeneity to support integration and uniform query interfaces. Complicating factors with respect to conventional view integration techniques are related to the fact that the sources to be integrated already exist and that semantic heterogeneity occurs on the large-scale, involving terminology, structure, and context of the involved sources, with respect to geographical, organizational, and functional aspects related to information use. Moreover, to meet the requirements of global, Internet-based information systems, it is important that tools developed for supporting these activities are semi-automatic and scalable as much as possible. The goal of this paper is to describe the MOMIS [4, 5] (Mediator envirOnment for Multiple Information Sources) approach to the integration and query of multiple, heterogeneous information sources, containing structured and semistructured data. MOMIS has been conceived as a joint collaboration between University of Milano and Modena in the framework of the INTERDATA national research project, aiming at providing methods and tools for data management in Internet-based information systems. Like other integration projects [1, 10, 14], MOMIS follows a “semantic approach” to information integration based on the conceptual schema, or metadata, of the information sources, and on the following architectural elements: i) a common object-oriented data model, defined according to the ODL<subscrpt><italic>I</italic><supscrpt>3</supscrpt></subscrpt> language, to describe source schemas for integration purposes. The data model and ODL<subscrpt><italic>I</italic><supscrpt>3</supscrpt></subscrpt> have been defined in MOMIS as subset of the ODMG-93 ones, following the proposal for a standard mediator language developed by the <italic>I</italic><supscrpt>3</supscrpt>/POB working group [7]. In addition, ODL<subscrpt><italic>I</italic><supscrpt>3</supscrpt></subscrpt> introduces new constructors to support the semantic integration process [4, 5]; ii) one or more wrappers, to translate schema descriptions into the common ODL<subscrpt><italic>I</italic><supscrpt>3</supscrpt></subscrpt> representation; iii) a mediator and a query-processing component, based on two pre-existing tools, namely ARTEMIS [8] and ODB-Tools [3] (available on Internet at http://sparc20.dsi.unimo.it/), to provide an <italic>I</italic><supscrpt>3</supscrpt> architecture for integration and query optimization. In this paper, we focus on capturing and reasoning about semantic aspects of schema descriptions of heterogeneous information sources for supporting integration and query optimization. Both semistructured and structured data sources are taken into account [5]. A Common Thesaurus is constructed, which has the role of a shared ontology for the information sources. The Common Thesaurus is built by analyzing ODL<subscrpt><italic>I</italic><supscrpt>3</supscrpt></subscrpt> descriptions of the sources, by exploiting the Description Logics OLCD (Object Language with Complements allowing Descriptive cycles) [2, 6], derived from KL-ONE family [17]. The knowledge in the Common Thesaurus is then exploited for the identification of semantically related information in ODL<subscrpt><italic>I</italic><supscrpt>3</supscrpt></subscrpt> descriptions of different sources and for their integration at the global level. Mapping rules and integrity constraints are defined at the global level to express the relationships holding between the integrated description and the sources descriptions. ODB-Tools, supporting OLCD and description logic inference techniques, allows the analysis of sources descriptions for generating a consistent Common Thesaurus and provides support for semantic optimization of queries at the global level, based on defined mapping rules and integrity constraints.

Semantic integration of heterogeneous information sources

Abstract Developing intelligent tools for the integration of information extracted from multiple heterogeneous sources is a challenging issue to effectively exploit the numerous sources available on-line in global information systems. In this paper, we propose intelligent, tool-supported techniques to information extraction and integration from both structured and semistructured data sources. An object-oriented language, with an underlying Description Logic, called ODLI3, derived from the standard ODMG is introduced for information extraction. ODLI3 descriptions of the source schemas are exploited first to set a Common Thesaurus for the sources. Information integration is then performed in a semiautomatic way by exploiting the knowledge in the Common Thesaurus and ODLI3 descriptions of source schemas with a combination of clustering techniques and Description Logics. This integration process gives rise to a virtual integrated view of the underlying sources for which mapping rules and integrity constraints are specified to handle heterogeneity. Integration techniques described in the paper are provided in the framework of the MOMIS system based on a conventional wrapper/mediator architecture.

Agents and Peer-to-Peer Computing

Invited Paper.- Information Flow Analysis in Autonomous Agent and Peer-to-Peer Systems for Self-organizing Electronic Health Records.- P2P Infrastructure.- Hybrid DHT Design for Mobile Environments.- DANTE: A Self-adapting Peer-to-Peer System.- The Exclusion of Malicious Routing Peers in Structured P2P Systems.- Agents in P2P.- Cooperative CBR System for Peer Agent Committee Formation.- Mobile Agent-Based Approach for Resource Discovery in Peer-to-Peer Networks.- P2P Search.- Chora: Expert-Based P2P Web Search.- K-link: A Peer-to-Peer Solution for Organizational Knowledge Management.- An Analysis of Interest-Community Facilitated Peer-to-Peer Search.- Applications.- Mitigating the Impact of Liars by Reflecting Peers Credibility on P2P File Reputation Systems.- A Comparative Study of Reasoning Techniques for Service Selection.- PROSA: P2P Resource Organisation by Social Acquaintances.- Reliable P2P File Sharing Service.- Studying Viable Free Markets in Peer-to-Peer File Exchange Applications without Altruistic Agents.- Distributed Multi-layered Network Management for NEC Using Multi-Agent Systems.- Facilitating Collaboration in a Distributed Software Development Environment Using P2P Architecture.- A Peer to Peer Grid Computing System Based on Mobile Agents.

On taxonomic reasoning in conceptual design

Taxonomic reasoning is a typical task performed by many AI knowledge representation systems. In this paper, the effectiveness of taxonomic reasoning techniques as an active support to knowledge acquisition and conceptual schema design is shown. The idea developed is that by extending conceptual models with defined concepts and giving them rigorous logic semantics, it is possible to infer isa relationships between concepts on the basis of their descriptions. From a theoretical point of view, this approach makes it possible to give a formal definition for consistency and minimality of a conceptual schema. From a pragmatic point of view it is possible to develop an active environment that allows automatic classification of a new concept in the right position of a given taxonomy, ensuring the consistency and minimality of a conceptual schema. A formalism that includes the data semantics of models giving prominence to type constructors (E/R, TAXIS, GALILEO) and algorithms for taxonomic inferences are presented: their soundness, completeness, and tractability properties are proved. Finally, an extended formalism and taxonomic inference algorithms for models giving prominence to attributes (FDM, IFO) are given.

Synthesizing an integrated ontology

The Mediator Environment for Multiple Information Sources (Momis) supports semiautomatic building, annotation, and extension of domain ontologies.

Keyword search over relational databases: a metadata approach

Keyword queries offer a convenient alternative to traditional SQL in querying relational databases with large, often unknown, schemas and instances. The challenge in answering such queries is to discover their intended semantics, construct the SQL queries that describe them and used them to retrieve the respective tuples. Existing approaches typically rely on indices built a-priori on the database content. This seriously limits their applicability if a-priori access to the database content is not possible. Examples include the on-line databases accessed through web interface, or the sources in information integration systems that operate behind wrappers with specific query capabilities. Furthermore, existing literature has not studied to its full extend the inter-dependencies across the ways the different keywords are mapped into the database values and schema elements. In this work, we describe a novel technique for translating keyword queries into SQL based on the Munkres (a.k.a. Hungarian) algorithm. Our approach not only tackles the above two limitations, but it offers significant improvements in the identification of the semantically meaningful SQL queries that describe the intended keyword query semantics. We provide details of the technique implementation and an extensive experimental evaluation.

Description logics for semantic query optimization in object-oriented database systems

Semantic query optimization uses semantic knowledge (i.e., integrity constraints) to transform a query into an equivalent one that may be answered more efficiently. This article proposes a general method for semantic query optimization in the framework of Object-Oriented Database Systems. The method is effective for a large class of queries, including conjunctive recursive queries expressed with regular path expressions and is based on three ingredients. The first is a Description Logic, ODLRE, providing a type system capable of expressing: class descriptions, queries, views, integrity constraint rules and inference techniques, such as incoherence detection and subsumption computation. The second is a semantic expansion function for queries, which incorporates restrictions logically implied by the query and the schema (classes + rules) in one query. The third is an optimal rewriting method of a query with respect to the schema classes that rewrites a query into an equivalent one, by determining more specialized classes to be accessed and by reducing the number of factors. We implemented the method in a tool providing an ODMG-compliant interface that allows a full interaction with OQL queries, wrapping underlying Description Logic representation and techniques to the user.

Consistency checking in complex object database schemata with integrity constraints

Integrity constraints are rules that should guarantee the integrity of a database. Provided an adequate mechanism to express them is available, the following question arises: is there any way to populate a database which satisfies the constraints supplied by a database designer? That is, does the database schema, including constraints, admit at least a nonempty model? This work answers the above question in a complex object database environment, providing a theoretical framework, including the following ingredients: (1) two alternative formalisms, able to express a relevant set of state integrity constraints with a declarative style; (2) two specialized reasoners, based on the tableaux calculus, able to check the consistency of complex objects database schemata expressed with the two formalisms. The proposed formalisms share a common kernel, which supports complex objects and object identifiers, and which allow the expression of acyclic descriptions of: classes, nested relations and views, built up by means of the recursive use of record, quantified set, and object type constructors and by the intersection, union, and complement operators. Furthermore, the kernel formalism allows the declarative formulation of typing constraints and integrity rules. In order to improve the expressiveness and maintain the decidability of the reasoning activities, we extend the kernel formalism into two alternative directions. The first formalism, OLCP, introduces the capability of expressing path relations. Because cyclic schemas are extremely useful, we introduce a second formalism, OLCD, with the capability of expressing cyclic descriptions but disallowing the expression of path relations. In fact, we show that the reasoning activity in OLCDP (i.e., OLCP with cycles) is undecidable.

An information integration framework for e-commerce

One of the main challenges for e-commerce infrastructure designers is to retrieve data from different sources and create a unified view that overcomes contradictions and redundancies. Virtual catalogs, such as the Momis project, can help synthesize data and present it in a unified manner to the customer.

ODB-QOPTIMIZER: a tool for semantic query optimization in OODB

ODB-QOPTIMIZER is a ODMG 93 compliant tool for the schema validation and semantic query optimization. The approach is based on two fundamental ingredients. The first one is the OCDL description logics (DLs) proposed as a common formalism to express class descriptions, a relevant set of integrity constraint rules (IC rules) and queries. The second one are DLs inference techniques, exploited to evaluate the logical implications expressed by IC rules and thus to produce the semantic expansion of a given query.