The multi-layered architecture of the DArmStadt Data Base System (DASDBS) for advanced applications is introduced DASDBS is conceived as a family of application-specific database systems on top of a common database kernel system. The main design problem considered here is, What features are common enough to be integrated into the kernel and what features are rather application-specific? Kernel features must be simple enough to be efficiently implemented and to serve a broad class of clients, yet powerful enough to form a convenient basis for application-oriented layers. Our kernel provides mechanisms to efficiently store hierarchically structured complex objects, and offers operations which are set-oriented and can be processed in a single scan through the objects. To achieve high concurrency in a layered system, a multi-level transaction methodology is applied. First experiences with our current implementation and some lessons we have learned from it are reported.

The signature approach is an access method for partial-match retrieval which meets many requirements of an office environment. Signatures are hash coded binary words derived from objects stored in the data base. They serve as a filter for retrieval in order to discard a large number of nonqualifying objects. In an indexed signature method the signatures of objects stored on a single page are used to form a signature for that page. In this paper we describe a new technique of indexed signatures which combines the dynamic balancing of B-trees with the signature approach. The main problem of appropriate splitting is solved in a heuristic way. Operations are described and a simple performance analysis is given. The analysis and some experimental results indicate a considerable performance gain. Moreover, the new S-tree approach supports a clustering on a signature basis. Further remarks on adaptability complete this work.