Interner Bericht des Fachbereich Informatik
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20
Partitioned chain grammars
(1979)
This paper introduces a new class of grammars, the partitioned chain grammars, for which efficient parsers can be automatically generated. Besides being efficiently parsable these grammars possess a number of other properties, which make them very attractive for the use in parser-generators. They for instance form a large grammarclass and describe all deterministic context-free languages. Main advantage of the partitioned chain grammars however is, that given a language it is usually easier to describe it by a partitioned chain grammar than to construct a grammar of some other type commonly used in parser-generators for it.
213
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.
216
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.
223
Gauss Frame Offsets
(1992)
225
Virtual Reality (VR) is to be seen as the superset of simulation and animation. Visualization is done by rendering. The fundamental model of VR accounts for all phenomenons to be modelled with help of a computer. Examples range from simple dragging actions with a mouse device to the complex simulation of physically based animation.
222
User interfaces for large distributed applications have to handle specific problems: the complexity of the application itself and the integration of online-data into the user interface. A main task of the user interface architecture is to provide powerful tools to design and augment the end-user system easily, hence giving the designer more time to focus on user requirements. Our experiences developing a user interface system for a process control room showed that a lot of time during the development process is wasted for the integration of online-data residing anywhere but not in the user interface itself. Furtheron external data may be kept by different kinds of programs, e.g. C-programs running
a numerical process model or PROLOG-programs running a diagnosis system, both in parallel to the process and in parallel to the user interface. Facing these specific requirements, we developed a user interface architecture following two main goals: 1. integration of external information into high-level graphical objects and 2. the system should be open for any program running as a separate process using its own problem-oriented language. The architecture is based on two approaches: an asynchronous, distributed and language independent communication model and an object model describing the problem domain and the interface using object-oriented techniques. Other areas like rule-based programming are involved, too. With this paper, we will present the XAVIA user interface architecture, the (as far as we know) first user inteface architecture, which is consequently based on a distributed object model.
233
This paper describes some new algorithms for the accurate calculation of surface properties. In the first part an arithmetic on Bézier surfaces is introduced. Formulas are given, which determine the Bézier points and weights of the resulting surface from the points and weights of the operand surfaces. An application of the arithmetic operations to the surface interrogation methods are described in the second part. It turns out, that the quality analysis can be reduced to a few numerical stable operations. Finally the advantages and disadvantages of this method are discussed.
235
The composition of Bézier curves and tensor product Bézier surfaces, polynomial as well as rational, is applied to exactly and explicitely represent trim curves of tensor product Bézier surfaces. Trimming curves are assumed to be defined as Bézier curves in surface parameter domain. A Bézier spline approximation of lower polynomial degree is built up as weil which is based on the exact trim curve representation in coordinate space.