Karen Villaverde

A methodology for order-sensitive execution of non-deterministic languages on Beowulf platforms

We propose a novel methodology, based on stack splitting, to efficiently support order-sensitive computations (e.g., I/O, side-effects) during search-parallel execution of non-deterministic languages on Beowulf platforms. The methodology has been validated in the context of the PALS Prolog system and results on a Pentium Beowulf are discussed.

PALS: An Or-Parallel Implementation of Prolog on Beowulf Architectures

This paper describes the development of the PALS system, an implementation of Prolog that efficiently exploits or-parallelism on share-nothing platforms. PALS makes use of a novel technique, called incremental stack-splitting. The technique builds on the stack-splitting approach, which in turn is an evolution of the stack-copying method used in a variety of parallel logic systems. This is the first distributed implementation based on the stack-splitting method ever realized. Experimental results obtained on a Beowulf system are presented and analyzed.

Exact Bounds for Interval and Fuzzy Functions Under Monotonicity Constraints, with Potential Applications to Biostratigraphy

The age of fossil species in samples recovered from a well that penetrates an undisturbed sequence of sedimentary rocks increases with depth. The results of biostratigraphic analysis of such a sequence consist of several age-depth values - both known with interval (or fuzzy) uncertainty - and we would like to find, for each possible depth, the interval of the possible values of the corresponding age. A similar problem of bounding an intervally (fuzzily) defined function under monotonicity constraint occurs in many other application areas. In this paper, we provide an efficient algorithm for solving this problem

Incremental stack-splitting mechanisms for efficient parallel implementation of search-based AI systems

Incremental stack-copying is a technique which has been successfully used to support efficient parallel execution of a variety of search-based Al systems-e.g., logic-based and constraint-based systems. The idea of incremental stack-copying is to only copy the difference between the data areas of two agents, instead of copying them entirely, when distributing parallel work. In order to further reduce the communication during stack-copying and make its implementation efficient on message-passing platforms, a new technique, called stack-splitting, has recently been proposed. In this paper, we describe a scheme to effectively combine stack-splitting with incremental stack copying, to achieve superior parallel performance in a non-shared memory environment. We also describe a scheduling scheme for this incremental stack-splitting strategy. These techniques are currently being implemented in the PALS system-a parallel constraint logic programming system.

How to tell when a product of two partially ordered spaces has a certain property: General results with application to fuzzy logic

In this paper, we describe how checking whether a given property F is true for a product A1 × A2 of partially ordered spaces can be reduced to checking several related properties of the original spaces Ai. This result in useful in fuzzy logic, where, to compare our degree of confidence in several statements, we often need to combine relative confidence comparison results provided by different experts. For example, Cartesian product corresponds to the cautious approach, when our confidence in S′ is higher than confidence in S if and only if all the experts are more confident in S′ than in S. Alternatively, if we have an absolute confidence in the first expert and we use the opinion of the second expert only if the first expert cannot decide, we get a lexicographic product.

Cheshire: Towards an Alice Based Game Development Tool

This paper presents on-going research that aims to modify the open source 3D programming environment Alice in order to adapt it for use as a development tool for teaching game programming. The advantages and disadvantages of the current version of Alice for game development are described, along with an account of experiences using Alice for game development in the classroom. We set forth the changes that we plan to make to Alice and the challenges that we are facing.

Why Ellipsoid Constraints, Ellipsoid Clusters, and Riemannian Space-Time: Dvoretzky’s Theorem Revisited

In many practical applications, we encounter ellipsoid constraints, ellipsoid-shaped clusters, etc. A usual justification for this ellipsoid shape comes from the fact that many real-life quantities are normally distributed, and for a multi-variate normal distribution, a natural confidence set (containing the vast majority of the objects) is an ellipsoid. However, ellipsoids appear more frequently than normal distributions (which occur in about half of the cases). In this paper, we provide a new justification for ellipsoids based on a known mathematical result – Dvoretzky’s Theorem.

Towards a new justification of the Tastle-Wierman (TW) dissention and consensus measures (and their potential role in education)

To estimate how close the estimates of different experts are, W. J. Tastle and M. J. Wierman proposed numerical measures of dissention and consensus, and showed that these measures indeed capture the intuitive ideas of dissent and consensus. In this paper, we show that the Tastle-Wierman formulas can be naturally derived from the basic formulas of fuzzy logic. We also show that these formulas can be used in education, to describe how different the grades of different students are.

Towards more detailed value-added teacher assessments

Sometimes, the efficiency of a class is assessed by assessing the amount of knowledge that the students have after taking this class. However, this amount depends not only on the quality of the class, but also on how prepared were the students when they started taking this class. A more adequate assessment should therefore be value-added, estimating the added value that the class brought to the students. In pedagogical practice, there are many value-added assessment models. However, most existing models have two limitations. First, they model the effect of the class as an additive factor independent on the initial knowledge. In reality, the amount of knowledge learned depends on the amount of the initial knowledge. Second, the existing models are statistical, they implicitly assume that the assessment values are objective — and are subject to random measurement errors and noises. In reality, many assessment values are subjective. Thus, fuzzy techniques provide, in our opinion, a more adequate way of processing these values. In this paper, we describe how the use of fuzzy techniques can help us overcome both limitations of the existing value-added assessments.

PALS: Efficient Or-Parallel execution of Prolog on Beowulf clusters

This paper describes the development of the PALS system, an implementation of Prolog capable of efficiently exploiting or-parallelism on distributed-memory platforms—specifically Beowulf clusters. PALS makes use of a novel technique, called incremental stack-splitting. The technique proposed builds on the stack-splitting approach, previously described by the authors and experimentally validated on shared-memory systems, which in turn is an evolution of the stack-copying method used in a variety of parallel logic and constraint systems—e.g., MUSE, YAP, and Penny. The PALS system is the first distributed or-parallel implementation of Prolog based on the stack-splitting method ever realized. The results presented confirm the superiority of this method as a simple yet effective technique to transition from shared-memory to distributed-memory systems. PALS extends stack-splitting by combining it with incremental copying; the paper provides a description of the implementation of PALS, including details of how distributed scheduling is handled. We also investigate methodologies to effectively support order-sensitive predicates (e.g., side-effects) in the context of the stack-splitting scheme. Experimental results obtained from running PALS on both Shared Memory and Beowulf systems are presented and analyzed.