Optimization of Spatial Joins Using Filters

When viewing present-day technical applications that rely on the use of database systems, one notices that new techniques must be integrated in database management systems to be able to support these applications efficiently. This paper discusses one of these techniques in the context of supporting a Geographic Information System. It is known that the use of filters on geometric objects has a significant impact on the processing of 2-way spatial join queries. For this purpose, filters require approximations of objects. Queries can be optimized by filtering data not with just one but with several filters. Existing join methods are based on a combination of filters and a spatial index. The index is used to reduce the cost of the filter step and to minimize the cost of retrieving geometric objects from disk. In this paper we examine n-way spatial joins. Complex n-way spatial join queries require solving several 2-way joins of intermediate results. In this case, not only the profit gained from using both filters and spatial indices but also the additional cost due to using these techniques are examined. For 2-way joins of base relations these costs are considered part of physical database design. We focus on the criteria for mutually comparing filters and not on those for spatial indices. Important aspects of a multi-step filter-based n-way spatial join method are described together with performance experiments. The winning join method uses several filters with approximations that are constructed by rotating two parallel lines around the object

Incremental Evaluation of Rules and its Relationship to Parallelism

Rule interpreters usually start with an initial database and perform the inference procedure in cycles, ending with a final database. In a real time environment it is possible to receive updates to the initial database after the inference procedure has started or even after it has ended. We present an algorithm for incremental maintenance of the deductive database in the presence of such updates. Interestingly, the same algorithm is useful for parallel and distributed rule processing in the following sense. \\'hen the processors evaluating a program operate asynchronously. then they may have different views of the database. The incremental maintenance procedure we present can be used to synchronize these views

Database research at the University of Twente

The University of Twente is one of the leading technical universities in the Netherlands. It is the only Dutch university that has an independent computerscience department. The database research group is comprised of approximately 15 researchers and graduate students. It is participating in a number of externally funded, national and international research projecs, and has done so in the recent past. The research interests of the database group are in the field of object-oriented, logical and extended relational systems. The three main points of interest are: i) development of well-founded (objed-oriented) data models and tools, ii) design of and optimization in database systems, with a strong emphasis on distribution aspects, and iii) database support for new (technical) applications. In the following, We will give a brief description of our main research efforts, and mention some of the associated publications