Parallel Evaluation of Multi-join Queries

A number of execution strategies for parallel evaluation of multi-join queries have been proposed in the literature. In this paper we give a comparative performance evaluation of four execution strategies by implementing all of them on the same parallel database system, PRISMA/DB. Experiments have been done up to 80 processors. These strategies, coming from the literature, are named: Sequential Parallel, Synchronous Execution, Segmented Right-Deep, and Full Parallel. Based on the experiments clear guidelines are given when to use which strategy. This is an extended abstract; the full paper appeared in Proc. ACM SIGMOD'94, Minneapolis, Minnesota, May 24–27, 199

Searching documents on the intranet

Searching for documents on the internet with today’s search engines, which are mainly based on words in a document, is not satisfactory. Results can be improved by also taking the content of a document into account. The Extensible Markup Language (XML) enables us to do semantic tagging and to make the structure of a document explicit. But this describes a document only at the syntactical level. A more ideal situation would be when the XML tagging is also used to define the document at the semantical level. To realize this we allow an author of a document to describe the relevant concepts by means of tags like he would design an object-oriented database schema. In our approach a user searching for a particular document is presented a graphical description of such a schema, that describes the concepts defined for the webspace of an intranet. Via this interface the user can formulate OO-like queries or navigate to relevant web pages. To realize our ideas we are building an architecture based on the concept of an index-database. A prototype is up and running

ADL - An Algebraic Database Language

In this paper we present the language ADL \Gamma an algebraic database query language for complex objects. Non-administrative database applications pose new requirements on database languages with respect to modelling capability, deductive capability, and performance. To meet those new requirements, on the front end increasingly powerful database programming languages are being defined. On the backend a lot of research is directed towards investigation of the opportunities multi-processor systems offer for database systems. ADL is designed as an intermediate algebraic optimization language to bridge the gap between those new programming languages, which often are of a declarative nature, and the increasingly complex system architectures. The language supports a rich collection of data types including set, list, tuple, variant, object and reference types. With these types, a collection of powerful, set-oriented algebraic operators is defined. Deductive capability will be further increas..

Modelling the Webspace of an Intranet

Searching the internet using the currently available search engines is not satisfactory. The techniques used there focus on the extraction of relevant information directly from the documents available on the web. We introduce a new approach, which aims at describing the content of a webspace, formed by a collection of related documents, instead of looking at the single documents. By identifying concepts and the relationships among them, the content of a webspace is described semantically in a schema for the webspace. The main objective is that by following this approach we can start querying the content of a collection of related documents rather than the content of a single document. In this paper we introduce a model for the webspace that allows us to describe the concepts at a semantical level, in terms of classes, associations over classes, and attributes of classes. At the syntactical level we use XML, to describe information as instantiations of the concepts defined in the websp..

Reverse Engineering of Relational Database Applications

Abstract. This paper presents techniques for reverse engineering of relational database applications. The target of such an effort is the definition of a fully equipped object-oriented view of the relational database, including methods and constraints. Such views can be seen as a full specification of the database semantics, aiding for example in the identification of semantic heterogeneity among interoperable databases. The general problem of translating from an imperative programming language environment to a declarative context such as provided by our target OODML is very hard. However, we show that the specific features of database application software allow for the development of a framework geared towards the particular problems encountered in this context.