An Envisioned Approach for Modeling and Supporting User-Centric Query Activities on Data Warehouses

In this vision paper, the authors discuss models and techniques for integrating, processing and querying data, information and knowledge within data warehouses in a user-centric manner. The user-centric emphasis allows us to achieve a number of clear advantages with respect to classical data warehouse architectures, whose most relevant ones are the following: (i) a unified and meaningful representation of multidimensional data and knowledge patterns throughout the data warehouse layers (i.e., loading, storage, metadata, etc); (ii) advanced query mechanisms and guidance that are capable of extracting targeted information and knowledge by means of innovative information retrieval and data mining techniques. Following this main framework, the authors first outline the importance of knowledge representation and management in data warehouses, where knowledge is expressed by existing ontology or patterns discovered from data. Then, the authors propose a user-centric architecture for OLAP query processing, which is the typical applicative interface to data warehouse systems. Finally, the authors propose insights towards cooperative query answering that make use of knowledge management principles and exploit the peculiarities of data warehouses (e.g., multidimensionality, multi-resolution, and so forth).

An Integrated Query Relaxation Approach Adopting Data Abstraction and Fuzzy Relation

This paper proposes a cooperative query answering approach that relaxes query conditions to provide approximate answers by utilizing similarity relationships between data values. The proposed fuzzy abstraction hierarchy (FAH) represents a similarity relationship based on the integrated notion of data abstraction and fuzzy relations. Based on FAH, the authors develop query relaxation operators like query generalization, approximation, and specialization of a value. Compared with existing approaches, FAH supports more effective information retrieval by processing various kinds of cooperative queries through elaborate relaxation control and providing ranked query results according to fitness scores. Moreover, FAH reduces maintenance cost by decreasing the number of similarity relationships to be managed.

Consistent Queries over Databases with Integrity Constraints

Integrating data from different sources consists of two main steps, the first in which the various relations are merged together, and the second in which some tuples are removed (or inserted) from the resulting database in order to satisfy integrity constraints. There are several ways to integrate databases or possibly distributed information sources, but whatever integration architecture we choose, the heterogeneity of the sources to be integrated causes subtle problems. In particular, the database obtained from the integration process may be inconsistent with respect to integrity constraints, that is, one or more integrity constraints are not satisfied. Integrity constraints represent an important source of information about the real world. They are usually used to define constraints on data (functional dependencies, inclusion dependencies, etc.) and have, nowadays, a wide applicability in several contexts such as semantic query optimization, cooperative query answering, database integration, and view update. Since the satisfaction of integrity constraints cannot generally be guaranteed, if the database is obtained from the integration of different information sources, in the evaluation of queries, we must compute answers that are consistent with the integrity constraints. The following example shows a case of inconsistency. Example 1: Consider the following database schema consisting of the single binary relation Teaches (Course, Professor) where the attribute Course is a key for the relation. Assume there are two different instances for the relations Teaches, D1={(c1,p1),(c2,p2)} and D2={(c1,p1),(c2,p3)}. The two instances satisfy the constraint that Course is a key, but from their union we derive a relation that does not satisfy the constraint since there are two distinct tuples with the same value for the attribute Course. In the integration of two conflicting databases simple solutions could be based on the definition of preference criteria such as a partial order on the source information or a majority criterion (Lin & Mendelzon, 1996). However, these solutions are not generally satisfactory, and more useful solutions are those based on (1) the computation of “repairs” for the database, and (2) the computation of consistent answers (Arenas, Bertossi, & Chomicki, 1999). The computation of repairs is based on the definition of minimal sets of insertion and deletion operations so that the resulting database satisfies all constraints. The computation of consistent answers is based on the identification of tuples satisfying integrity constraints and on the selection of tuples matching the goal. For instance, for the integrated database of Example 1, we have two alternative repairs consisting in the deletion of one of the tuples (c2,p2) and (c2,p3). The consistent answer to a query over the relation Teaches contains the unique tuple (c1,p1) so that we do not know which professor teaches course c2. Therefore, it is very important, in the presence of inconsistent data, not only to compute the set of consistent answers, but also to know which facts are unknown and if there are possible repairs for the database.

An Integrated Query Relaxation Approach Adopting Data Abstraction and Fuzzy Relation

This paper proposes a cooperative query answering approach that relaxes query conditions to provide approximate answers by utilizing similarity relationships between data values. The proposed fuzzy abstraction hierarchy (FAH) represents a similarity relationship based on the integrated notion of data abstraction and fuzzy relations. Based on FAH, the authors develop query relaxation operators like query generalization, approximation, and specialization of a value. Compared with existing approaches, FAH supports more effective information retrieval by processing various kinds of cooperative queries through elaborate relaxation control and providing ranked query results according to fitness scores. Moreover, FAH reduces maintenance cost by decreasing the number of similarity relationships to be managed.

Consistent Queries over Databases with Integrity Constraints

Integrating data from different sources consists of two main steps, the first in which the various relations are merged together, and the second in which some tuples are removed (or inserted) from the resulting database in order to satisfy integrity constraints. There are several ways to integrate databases or possibly distributed information sources, but whatever integration architecture we choose, the heterogeneity of the sources to be integrated causes subtle problems. In particular, the database obtained from the integration process may be inconsistent with respect to integrity constraints, that is, one or more integrity constraints are not satisfied. Integrity constraints represent an important source of information about the real world. They are usually used to define constraints on data (functional dependencies, inclusion dependencies, etc.) and have, nowadays, a wide applicability in several contexts such as semantic query optimization, cooperative query answering, database integration, and view update.