Henk M. Blanken

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Recently, extensions for relational database management systems (DBMS) have been proposed to support also hierarchical structures (complex objects). These extensions have been mainly implemented on top of an existing DBMS. Such an approach leads to many disadvantages not only from the conceptual point of view but also from performance aspects. Thus paper(More)
Most declarative SQL-like query languages for object-oriented database systems (OOSQL) are orthogonal languages allowing for arbitrary nesting of expressions in the select-, from-, and where-clause. Expressions in the from-clause may be base tables as well as setvalued attributes. In this paper, we propose a general strategy for the optimization of nested(More)
The execution of a query in a parallel database machine can be controlled in either a control flow way, or in a data flow way. In the former case a single system node controls the entire query execution. In the latter case the processes that execute the query, although possibly running on different nodes of the system, trigger each other. Lately, many(More)
This paper presents a framework for architecture alignment that can be positioned between approaches for software architecture, which concern software artefacts only, and strategic alignment models, which have a business focus. The framework is currently applied in case study research to find alignment patterns used in practice. First results presented in(More)
Transformation of nested SQL queries into join queries is advantageous because a nested SQL query can be looked upon as a nested-loop join, which is just one of the several join implementations that may be available in a relational DBMS. In join queries, dangling (unmatched) operand tuples are lost, which causes a problem in transforming nested queries(More)
An important problem in the physical design of databases is the selection of secondary indices. In general, this problem cannot be solved in an optimal way due to the complexity of the selection process. Often use is made of heuristics such as the well-known ADD and DROP algorithms. In this paper it will be shown that frequently used cost functions can be(More)
Sunil Choenni1 Elisa Bertino2 Henk M. Blanken1 Thiel Chang3 1University of Twente 2University of Genova 3G.A.K. P.O. Box 217, 7500 AE Enschede, Via L.B. Alberti 4, 16132 Genova, P.O. Box 8300, 1005 CA Amsterdam, The Netherlands Italy The Netherlands Abstract An operation in object-oriented databases gives rise to the processing of a path. Several database(More)
In optimizing database queries one inevitably encounters two important estimation problems. The first problem is to estimate the number of page accesses when selecting k tuples from a relation. The other problem is to estimate the number of different equijoin values remaining after selecting k tuples from a relation. The estimated values strongly depend on(More)