Paolo Tiberio

Physical database design for relational databases

This paper describes the concepts used in the implementation of DBDSGN, an experimental physical design tool for relational databases developed at the IBM San Jose Research Laboratory. Given a workload for System R (consisting of a set of SQL statements and their execution frequencies), DBDSGN suggests physical configurations for efficient performance. Each configuration consists of a set of indices and an ordering for each table. Workload statements are evaluated only for atomic configurations of indices, which have only one index per table. Costs for any configuration can be obtained from those of the atomic configurations. DBDSGN uses information supplied by the System R optimizer both to determine which columns might be worth indexing and to obtain estimates of the cost of executing statements in different configurations. The tool finds efficient solutions to the index-selection problem; if we assume the cost estimates supplied by the optimizer are the actual execution costs, it finds the optimal solution. Optionally, heuristics can be used to reduce execution time. The approach taken by DBDSGN in solving the index-selection problem for multiple-table statements significantly reduces the complexity of the problem. DBDSGNs principles were used in the Relational Design Tool (RDT), an IBM product based on DBDSGN, which performs design for SQL/DS, a relational system based on System R. System R actually uses DBDSGNs suggested solutions as the tool expects because cost estimates and other necessary information can be obtained from System R using a new SQL statement, the EXPLAIN statement. This illustrates how a system can export a model of its internal assumptions and behavior so that other systems (such as tools) can share this model.

Dynamic partitioning of signature files

The signature file access method has proved to be a convenient indexing technique, in particular for text data Because it can deal with unformatted data, many application domains have shown interest in signature file techniques, e.g., office information systems, statistical and logic databases. We argue that multimedia databases should also take advantage of this method, provided convenient storage structures for organizing signature tiles are available, Our main concern here is the dynamic organization of signatures based on a partitioning paradigm called Quick Filter. A signature file is partitioned by a hashing function and the partitions are orgamzed by linear hashing, Thorough performance evaluation of the new scheme is provided, and it is compared with single-level and multdevel storage structures Results show that quick filter is economical in space and very convenient for applications dealing with large files of dynamic data, and where user queries result in signatures with high weights. These characteristics are particularly interesting for multimedia databases, where integrated access to attributes, text and images must be provided.

Computer-Aided Analysis of Microwave Circuits

The most relevant techniques that have either found or should find useful application in analyzing microwave circuit performances in the frequency domain are surveyed. The particular needs of the microwave engineer are briefly discussed. Circuit equation formulations in terms of voltages and currents and wave variables are presented and the solution of the set of circuit equations by sparse-matrix techniques is illustrated. Methods based on multiport connection are also reviewed. The techniques for computing the first- and second-order sensitivity are illustrated and a comparison is made between the direct method and the transpose-matrix method, which is in certain cases similar to the method based on the adjoint circuit.

Temporal modelling and management of normative documents in XML format

In this paper, we present the results of a research project concerning the temporal management of normative texts in XML format. In particular, four temporal dimensions (publication, validity, efficacy and transaction times) are used to correctly represent the evolution of norms in time and their resulting versioning. Hence, we introduce a multiversion data model based on XML schema and define basic mechanisms for the maintenance and retrieval of multiversion norm texts. Finally, we describe a prototype management system which has been implemented and evaluated.

A temporal data model and management system for normative texts in XML format

In this paper,we present the results of an on-going research activity concerning the temporal management of normative texts in XML format. In particular, four temporal dimensions (publication,validity,efficacy and transaction times) are used to correctly represent the evolution of norms in time and their resulting versioning. Hence, we introduce a multiversion data model based on XML schema and de?ne basic mechanisms for the management of norm texts. Finally, we describe a prototype management system which has been implemented and evaluated.

Approximate Query Answering for a Heterogeneous XML Document Base

In this paper, we deal with the problem of effective search and query answering in heterogeneous web document bases containing documents in XML format of which the schemas are available. We propose a new solution for the structural approximation of the submitted queries which, in a preliminary schema matching process, is able to automatically identify the similarities between the involved schemas and to use them in the query processing phase, when a query written on a source schema is automatically rewritten in order to be compatible with the other useful XML documents. The proposed approach has been implemented in a web service and can deliver middleware rewriting services in any open-architecture XML repository system offering advanced search capabilities.

Declustering of key-based partitioned signature files

Access methods based on signature files can largely benefit from possibilities offered by parallel environments. To this end, an effective <italic>declustering</italic> strategy that would distribute signatures over a set of parallel independent disks has to be combined with a synergic <italic>clustering</italic> which is employed to avoid searching the whole signature file while executing a query. This article proposes two parallel signature file organizations, Hamming Filter (<italic>HF</italic>) and Hamming <supscrpt>+</supscrpt> Filter (<italic>H<supscrpt>+</supscrpt>F</italic>), whose common declustering strategy is based on <italic>error correcting codes</italic>, and where clustering is achieved by organizing signatures into fixed-size buckets, each containing signatures sharing the same <italic>key</italic> value. <italic>HF</italic> allocates signatures on disks in a static way and works well if a correct relationship holds between the parameters of the code and the size of the file. <italic>H<supscrpt>+</supscrpt>F</italic> is a generalization of <italic>HF</italic> suitable to manage highly dynamic files. It uses a dynamic declustering, obtained through a <italic>sequence</italic> of codes, and organizes a smooth migration of signatures between disks so that high performance levels are retained regardless of current file size. Theoretical analysis characterizes the best-case, expected, and worst-case behaviors of these organizations. Analytical results are verified by experiments on prototype systems.

Frame-sliced partitioned parallel signature files

The retrieval capabilities of the signature file access method have become very attractive for many data processing applications dealing with both formatted and unformatted data. However, performance is still a problem, mainly when large files are used and fast response required. In this paper, a high performance signature file organization is proposed, integrating the latest developments both in storage structure and parallel computing architectures. It combines horizontal and vertical approaches to the signature file fragmentation. In this way, a new, mixed decomposition scheme, particularly suitable for parallel implementation, is achieved. The organization, based on this fragmentation scheme, is called Fragmented Signature File. Performance analysis shows that this organization provides very good and relatively stable performance, covering the full range of possible queries. For the same degree of parallelism, it outperforms any other parallel signature file organization that has been defined so far. The proposed method also has other important advantages concerning processing of dynamic files, adaptability to the number of available processors, load balancing, and, to some extent, fault-tolerant query processing.

A syntactic approach for searching similarities within sentences

Textual data is the main electronic form of knowledge representation. Sentences, meant as logic units of meaningful word sequences, can be considered its backbone. In this paper, we propose a solution based on a purely syntactic approach for searching similarities within sentences, named approximate sub2sequence matching. This process being very time consuming, efficiency in retrieving the most similar parts available in large repositories of textual data is ensured by making use of new filtering techniques. As far as the design of the system is concerned, we chose a solution that allows us to deploy approximate sub2 sequence matching without changing the underlying database.

A method for hierarchy processing in relational systems

Abstract Processing of hierarchies has always been a difficult task in relational database environments. Several approaches have been proposed, but they have focused their attention mostly on improving the semantic power of relational systems in order to express recursive definitions on hierarchies rather than propose feasible computing methods. In this paper we show an encoding method which allows us to cope with one-to-many hierarchical relationships in a very different way. The novel idea is not to store the key of the parent tuple but create a code for the path of all the ancestor tuples. Two major advantages are thus obtained: a considerable reduction in the retrieval of unnecessary intermediate tuples, and an enrichment of the information that is utilized by the optimizer module to choose the best access strategy.