18315365
Towards a theory of collaborative multimedia
We develop a theory of media objects, and present optimal algorithms for collaborative synthesis of media objects. We then extend the algorithms to incorporate quality constraints (such as image size) as well as distribution across multiple nodes. The theoretical model is validated by an experimental implementation that supports the theoretical results.
629579
Query caching and optimization in distributed mediator systems
Query processing and optimization in mediator systems that access distributed non-proprietary sources pose many novel problems. Cost-based query optimization is hard because the mediator does not have access to source statistics information and furthermore it may not be easy to model the source's performance. At the same time, querying remote sources may be very expensive because of high connection overhead, long computation time, financial charges, and temporary unavailability. We propose a cost-based optimization technique that caches statistics of actual calls to the sources and consequently estimates the cost of the possible execution plans based on the statistics cache. We investigate issues pertaining to the design of the statistics cache and experimentally analyze various tradeoffs. We also present a query result caching mechanism that allows us to effectively use results of prior queries when the source is not readily available. We employ the novel invariants mechanism, which shows how semantic information about data sources may be used to discover cached query results of interest.
19021462
Combining Knowledge Bases Consisting of First Order Theories
Consider the construction of an expert system by encoding the knowledge of different experts. Suppose the knowledge provided by each expert is encoded into a knowledge base. Then the process of combining the knowledge of these different experts is an important and non-trivial problem. We study this problem here when the expert systems are considered to be first order theories. We present techniques for resolving inconsistencies in such knowledge bases. We also provide algorithms for implementing these techniques.
14637576
Heterogeneous active agents, III: Polynomially implementable agents
Abstract In “Heterogeneous active agents, I” (Eiter et al., 1999), two of the authors have introduced techniques to build agents on top of arbitrary data structures, and to “agentize” new/existing programs. They provided a series of successively more sophisticated semantics for such agent systems, and showed that as these semantics become epistemically more desirable, a computational price may need to be paid. In this paper, we identify a class of agents that are called weakly regular —this is done by first identifying a fragment of agent programs (Eiter et al., 1999) called weakly regular agent programs ( WRAP s for short). It is shown that WRAP s are definable via three parameters—checking for a property called “safety”, checking for a property called “conflict-freedom” and checking for a “deontic stratifiability” property. Algorithms for each of these are developed. A weakly regular agent is then defined in terms of these concepts, and a regular agent is one that satisfies an additional boundedness property. We then describe a polynomial algorithm that computes (under suitable assumptions) the reasonable status set semantics of regular agents—this semantics was identified by Eiter et al. (1999) as being epistemically most desirable. Though this semantics is coNP-complete for arbitrary agent programs (Eiter and Subrahmanian, 1999), it is polynomially computable via our algorithm for regular agents. Finally, we describe our implementation architecture and provide details of how we have implemented RAP s, together with experimental results.