Catálogo de publicaciones - libros

We study, in the context of object/relational mapping tools, the problem of describing mappings between inheritance hierarchies and relational schemas. To this end, we introduce a novel mapping model, called M^2ORM^2 + HIE , and investigate its mapping capabilities. We first show that M^2ORM^2 + HIE subsumes three well-know basic representation strategies for mapping a hierarchy to relations. We then show that M^2ORM^2 + HIE also allows expressing further mappings, e.g., where the three basic strategies are applied independently to different parts of a multi-level hierarchy. We describe the semantics of M^2ORM^2 + HIE in term of how CRUD (i.e., Create, Read, Update, and Delete) operations on objects (in a hierarchy) can be translated into operations over a corresponding relational database. We also investigate correctness conditions.

This paper presents a detailed integration process for XML schemata called BInXS. BInXS adopts a global-as-view integration approach that builds a global schema from a set of heterogeneous XML schemata related to a same application domain. This bottom-up approach maps all element and attribute definitions in XML schemata to correspondent concepts at the global schema, allowing access to all data available at the XML sources. The integration process is semi-automatically performed over conceptual representations of the XML schemata, which provides a better understanding of the semantics of the XML data to be unified. A conceptual schema is generated by a set of conversion rules that are applied to a schema definition for XML data. Once this conceptual schema is the result of a meticulous analysis of the XML logical model, it is able to abstract the particularities of semistructured and XML data, like elements with mixed contents and elements with alternative representations. Therefore, the further unification of such conceptual schemata implicitly deals with structural conflicts inherent to semistructured and XML data. In addition, BInXS supports a mapping strategy based on XPath expressions in order to maintain correspondences among global concepts and data at the XML sources.

Recently, the database and AI research communities have paid increased attention to ontologies . The main motivating reason is that ontologies promise solutions for complex problems caused by the lack of a good understanding of the semantics of data in many cases. In particular, ontologies have extensively been used to overcome the interoperability problem during the integration of heterogeneous information sources. Moreover, many efforts have been put into developing ontology based techniques for improving the query answering process in database and information systems. In this paper, we present a new approach for query processing within single (object) relational databases using ontology knowledge. Our goal is to process database queries in a semantically more meaningful way. In fact, our approach shows how an ontology can be effectively exploited to rewrite a user query into another one such that the new query provides more meaningful results satisfying the intention of the user. To this end, we develop a set of transformation rules which rely on semantic information extracted from the ontology associated with the database. In addition, we propose a semantic model and a set of criteria to prove the validity of the transformation results. We also address the necessary mappings between an ontology and its underlying database w.r.t. our framework.

In vague queries, a user enters a value that represents some real world object and expects as the result the set of database values that represent this real world object even with not exact matching. The problem appears in databases that collect data from different sources or databases were different users enter data directly. Query engines usually rely on the use of some type of similarity metric to support data with inexact matching. The problem of building query engines to execute vague queries has been already studied, but an important problem still remains open, namely that of defining the threshold to be used when a similarity scan is performed over a database column. From the bibliography it is known that the threshold depends on the similarity metrics and also on the set of values being queried. Thus, it is unrealistic to expect that the user supplies a threshold at query time. In this paper we propose a process for estimation of recall/precision values for several thresholds for a database column. The idea is that this process is started by a database administrator in a pre-processing phase using samples extracted from database. The meta-data collected by this process may be used in query processing in the optimization phase. The paper describes this process as well as experiments that were performed in order to evaluate it.

Tree structures provide a popular means to organize the information on the Web. Taxonomies of thematic categories, concept hierarchies, e-commerce product catalogs are examples of such structures. Querying multiple data sources that use tree structures to organize their data is a challenging issue due to name mismatches, structural differences and structural inconsistencies that occur in such structures, even for a single knowledge domain. In this paper, we present a method to query tree-structured data. We introduce dimensions which are sets of semantically related nodes in tree structures. Based on dimensions, we suggest dimension graphs. Dimension graphs can be automatically extracted from trees and abstract their structural information. They are semantically rich constructs that provide query guidance to pose and evaluate queries on trees. We design a query language to query tree-structured data. A key feature of this language is that queries are not restricted by the structure of the trees. We present a technique for evaluating queries and we provide necessary and sufficient conditions for checking query unsatisfiability. We also show how dimension graphs can be used to query multiple trees in the presence of structural differences and inconsistencies.

In the main, the attention of workflow researchers and workflow developers has focussed on the process perspective, i.e., control-flow. As a result, issues associated with the resource perspective, i.e., the people and machines actually doing the work, have been largely neglected. Although the process perspective is of most significance, appropriate consideration of the resource perspective is essential for successful implementation of workflow technology. Previous work has identified recurring, generic constructs in the control-flow and data perspectives, and presented them in the form of control-flow and data patterns. The next logical step is to describe workflow resource patterns that capture the various ways in which resources are represented and utilised in workflows. These patterns include a number of distinct groupings such as push patterns (“the system pushes work to a worker”) and pull patterns (“the worker pulls work from the system”) to describe the many ways in which work can be distributed. By delineating these patterns in a form that is independent of specific workflow technologies and modelling languages, we are able to provide a comprehensive treatment of the resource perspective and we subsequently use these patterns as the basis for a detailed comparison of a number of commercially available workflow management systems.

In this paper, a declarative foundation for process models is proposed. Three issues in process management and modeling are identified: business orientation, traceability, and flexibility. It is shown how these issues can be addressed by basing process models on business models, where a business model focuses on the transfer of value between agents. As a bridge between business models and process models, the notion of activity dependency model is introduced, which identifies, classifies, and relates activities needed for executing and coordinating value transfers.

Workflow management systems integrate applications and data resources in business processes. Frequently they have to keep local copies of data in the so called workflow repository. We introduce and define synchronization policies for these copies with their external data sources ranging from the provision of fully synchronized replications of external data sources to unsynchronized storage of read results. We analyze in detail the effects of combining various pull and push policies and show in an example how these policies can be used in different situations.

The focus of this paper is not on the requirements of an information system to be developed, but rather on the requirements that apply to the modelling techniques used during information system development. We claim that in past and present, many information systems modelling techniques have been developed without a proper understanding of the requirements that follow from the development processes in which these techniques are to be used. This paper provides a progress report on our research e.orts to obtain a fundamental understanding of the requirements mentioned. We discuss the underlying research issues, the research approach we use, the way of thinking ( weltanschauung ) that will be employed in finding the answers, and some first results.

It is widely acknowledged that the system functionality captured in a system model has to match organisational requirements available in the business model. However, fitness measures are rarely integrated in design methodologies. The paper proposes a framework to ease the generation of fitness measures adapted to a given methodology in order to quantify to which extent there is fit between the business and the system. The framework comprises a generic level and a specific level. The former provides generic evaluation criteria and metrics expressed on the basis of business and system ontologies. The specific level is dealing with a specific set of metrics adapted to specific business and system models. The paper presents the process for generating a specific set of measures from the generic set, illustrates it with two specific models and shows how the use of the generated metrics can help in making design decisions in the development of a hotel room booking system.