Kaiserslautern - Fachbereich Informatik
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Based on the experiences from an autonomous mobile robot project called MOBOT-III, we found hard realtime-constraints for the operating- system-design. ALBATROSS is "A flexible multi-tasking and realtime network-operating-system-kernel". The focusin this article is on a communication-scheme fulfilling the previous demanded assurances. The centralchapters discuss the shared buffer management and the way to design the communication architecture.Some further aspects beside the strict realtime-requirements like the possibilities to control and watch a running system, are mentioned. ALBATROSS is actually implemented on a multi-processor VMEbus-system.
Retrieval of cases is one important step within the case-based reasoning paradigm. We propose an improvement of this stage in the process model for finding most similar cases with an average effort of O[log2n], n number of cases. The basic idea of the algorithm is to use the heterogeneity of the search space for a density-based structuring and to employ this precomputed structure, a k-d tree, for efficient case retrieval according to a given similarity measure sim. In addition to illustrating the basic idea, we present the expe- rimental results of a comparison of four different k-d tree generating strategies as well as introduce the notion of virtual bounds as a new one that significantly reduces the retrieval effort from a more pragmatic perspective. The presented approach is fully implemented within the (Patdex) system, a case-based reasoning system for diagnostic applications in engineering domains.
Trimming of surfaces and volumes, curve and surface modeling via Bézier's idea of destortion, segmentation, reparametrization, geometric continuity are examples of applications of functional composition. This paper shows how to
compose polynomial and rational tensor product Bézier representations. The problem of composing Bezier splines and B-spline representations will also be addressed in this paper.
The use of non-volatile semiconductor memory within an extended storage hierarchy promises significant performance improvements for transaction processing. Although page-addressable semiconductor memories like extended memory, solid-state disks and disk caches are commercially available since several years, no detailed investigation of their use for transaction processing has been performed so far. We present a comprehensive simulation study that compares the performance of these storage types and of different usage forms. The following usage forms are considered: allocation of entire log and database files in non-volatile semiconductor memory, using a so-called write buffer to perform disk writes asynchronously, and caching of database pages at intermediate storage levels (in addition to main memory caching). Our simulations are conducted with both synthetically generated workloads and traces from real-life database applications. In particular, simulation results will be presented for the debit-credit workload frequently used in transaction processing benchmarks. As expected, the greatest performance improvements (but at the highest cost) can be achieved by storing log and database files completely in non-volatile semiconductor memory. For update-intensive
workloads, a limited amount of non-volatile memory used as a write buffer also proved to be very effective. To reduce the number of disk reads; caching of database pages in addition to main memory is best supported by an extended memory buffer. In this respect, disk caches are found to be less effective as they are designed for one-level caching. Different storage costs suggest that it may be cost-effective to use two or even three of the intermediate storage types together. The performance improvements obtainable by the use of non-volatile semiconductor memory is also found to reduce the need for sophisticated DBMS buffer management in order to achieve high transaction processing performance.