Secure Agents

With the rapid proliferation of software agents, there comes an increased need for agents to ensure that they do not provide data and/or services to unauthorized users. We first develop an abstract definition of what it means for an agent to preserve data/action security. Most often, this requires an agent to have knowledge that is impossible to acquire – hence, we then develop approximate security checks that take into account, the fact that an agent usually has incomplete/approximate beliefs about other agents. We develop two types of security checks – static ones that can be checked prior to deploying the agent, and dynamic ones that are executed at run time. We prove that a number of these problems are undecidable, but under certain conditions, they are decidable and (our definition of) security can be guaranteed. Finally, we propose a language within which the developer of an agent can specify her security needs, and present provably correct algorithms for static/dynamic security verification.     

Disjunctive LP+integrity constraints= stable model semantics

We show that stable models of logic programs may be viewed as minimal models of programs that satisfy certain additional constraints. To do so, we transform the normal programs into disjunctive logic programs and sets of integrity constraints. We show that the stable models of the normal program coincide with the minimal models of the disjunctive program thatsatisfy the integrity constraints. As a consequence, the stable model semantics can be characterized using theextended generalized closed world assumption for disjunctive logic programs. Using this result, we develop a bottomup algorithm for function-free logic programs to find all stable models of a normal program by computing the perfect models of a disjunctive stratified logic program and checking them for consistency with the integrity constraints. The integrity constraints provide a rationale as to why some normal logic programs have no stable models.     

The Advanced Video Information System: data structures and query processing

We describe how video data can be organized and structured so as to facilitate efficient querying. We develop a formal model for video data and show how spatial data structures, suitably modified, provide an elegant way of storing such data. We develop algorithms to process various kinds of video queries and show that, in most cases, the complexity of these algorithms is linear. A prototype system, called the Advanced Video Information System (AVIS), based on these concepts, has been designed at the University of Maryland.     

THE SCOPE OF DIMENSIONAL ANALYSIS IN QUALITATIVE REASONING

Dimensional analysis, traditionally used in physics and engineering to identify quantitative relationships, has recently been applied to qualitative reasoning of physical systems. We illustrate some problems of this approach. In the light of this, we reexamine the fundamentals of dimensional analysis in order to more precisely characterize its scope and limitations as a tool in qualitative reasoning. We also explore its relationship to state equation representations of physical systems. In particular, we describe its value in providing a set of constraints to reduce the ambiguity that bedevils qualitative reasoning schemes. We argue that dimensional analysis should not be seen as a substitute for knowledge about the physics but rather a supplement to other sources of knowledge.     

Guest Editorial

Multimedia Tools and Applications -     

An Algebra for PowerPoint Sources

There are now millions of PowerPoint documents available within corporate intranets and/or over the Internet. In this paper, we develop a formal model of PowerPoint databases. We propose a relational style algebra called pptA (PowerPoint Algebra) to query PowerPoint databases. The algebra contains some new operators (such as the APPLY operator that changes properties of objects, slides and presentations) as well as interesting twists on relational operators (e.g. join and cartesian product allow different entities being joined together to share attributes whose values may be merged). We prove a set of equivalence results within this algebra. We have implemented a version of pptA—the paper provides a cost model and experimental results on the conditions under which these equivalences are useful.     

An algebra for creating and querying multimedia presentations

Over the last few years, there has been a tremendous increase in the number of interactive multimedia presentations prepared by different individuals and organizations. In this paper, we present an algebra for creating and querying interactive multimedia presentation databases. This algebra operates on trees whose branches reflect different possible playouts of a set of presentations. The algebra not only extends all the classical relational operators to such databases, but also introduces a variety of novel operators for combining multiple presentations. As our algebra supports merging parts or all of existing presentations, this algebra can also be used as an authoring tool for creating multimedia presentations. We prove a host of equivalence results for queries in this algebra, which may be used to build query optimizers for interactive presentation databases.     

Creativity and scientific discovery with infused design and its analysis with C–K theory

Creativity is central to human activity and is a powerful force in personal and organizational success. Approaches to supporting creativity are diverse and numerous. The only way to understand the diversity and utility of these methods is through their careful analysis. The analysis conducted in this paper is done with the aid of a theory. As a first step, we use infused design (ID) method to generate new concepts and methods in the classic discipline of statics, in addition to its prior use in the generation of a number of creative designs. The use of the ID method in the creative scientific discovery process is modeled with C–K design theory, leading to better understanding of ID and C–K. The exercise in this paper illustrates how the synthesis of a theory, a framework, and methods that support discovery and design is useful in modeling and evaluation of creativity methods. Several topics for future research are described in the discussion.