6720403
The visual specification of context
We introduce a simple and novel visual technique for the specification of context in structured documents called T-graphs that we base on T-configurations in document trees. The technique is implemented in the current version of DESIGNER. Although we are applying this technique in the specification of context-dependent style sheets for HTML, XML, and SGML documents, it is clear that it can be used in other environments such as query specification for structured documents and for computer program transformations. We compare T-graphs with the context specification techniques found in other style-sheet systems and we also provide examples of context that we can and cannot specify with T-graphs. Although T-graphs are restrictive, they lend themselves to visual construction and modification, our main requirement when we designed this context specification method. We also investigate the time and space complexity of T-graph matching, a necessity for efficient implementation.
12635352
Planar Strong Visibility
Strong visibility is a generalization of standard visibility, defined with respect to a fixed set of line orientations. We investigate computational properties of this generalized visibility, as well as the related notion of strong convexity, and describe algorithms for the following tasks: 1. Testing the strong visibility of two points in a polygon. 2. Finding the strong convex hull of a point set or polygon. 3. Constructing the strong kernel of a polygon. 4. Identifying the points that are strongly visible from a given point.
29528938
Caterpillars: A Context Specification Technique
6984741
Bandwidth adaptive snooping
This paper advocates that cache coherence protocols use a bandwidth adaptive approach to adjust to varied system configurations (e.g., number of processors) and workload behaviors. We propose Bandwidth Adaptive Snooping Hybrid (BASH), a hybrid protocol that ranges from behaving like snooping (by broadcasting requests) when excess bandwidth is available to behaving like a directory protocol (by unicasting requests) when bandwidth is limited. BASH adapts dynamically by probabilistically deciding to broadcast or unicast on a per request basis using a local estimate of recent interconnection network utilization. Simulations of a microbenchmark and commercial and scientific workloads show that BASH robustly performs as well or better than the best of snooping and directory protocols as available bandwidth is varied. By mixing broadcasts and unicasts, BASH outperforms both snooping and directory protocols in the mid-range where a static choice of either is inefficient.
11025508
Hardware Support for Flexible Distributed Shared Memory
Workstation-based parallel systems are attractive due to their low cost and competitive uniprocessor performance. However, supporting a cache-coherent global address space on these systems involves significant overheads. We examine two approaches to coping with these overheads. First, DSM-specific hardware can be added to the off the-shelf component base to reduce overheads. Second, application-specific coherence protocols can avoid some overheads by exploiting programmer (or compiler) knowledge of an application's communication patterns. To explore the interaction between these approaches, we simulated four designs that add DSM acceleration hardware to a collection of off-the-shelf workstation nodes. Three of the designs support user-level software coherence protocols, enabling application-specific protocol optimizations. To verify the feasibility of our hardware approach, we constructed a prototype of the simplest design. Measured speedups from the prototype match simulation results closely. We find that, even with aggressive DSM hardware support, custom protocols can provide significant speedups for some applications. In addition, the custom protocols are generally effective at reducing the impact of other overheads, including those due to less aggressive hardware support and larger network latencies. However, for three of our benchmarks, the additional hardware acceleration provided by our most aggressive design avoid the need to develop more efficient custom protocols.
11947788
Context-Dependent L Forms
The notions of an EIL form and its interpretations are introduced. The resulting families of L systems and languages are studied from a number of different points of view. Some of the main results are: the family of context-free languages is generated by an EIL form (contrary to the earlier results concerning context-free L forms) and, as regards reducibility in the amount of context, EIL forms lie between IL and EIL systems.
21847551
Bounded Delay L Codes
Abstract Three natural notions of bounded delay for L codes are investigated. All interrelations, many of them rather surprising, between ordinary codes of bounded delay and L codes of bounded delay of various types are established.
14560983
Lower bounds for hot-potato permutation routing on trees
In this paper we consider hot-potato packet routing on trees. As a lower bound, for all sufficiently largen we construct a permutation routing problem on an n-node tree for which an oblivious greedy hot-potato algorithm requires at least 2n o n time steps. This lower bound is also valid for the minimumdistance heuristic. Applying the charging argument of Borodin et al. [8] we establish that any greedy hot-potato algorithm routes a permutation on a tree within 2 n 1 steps.