Abstract
Tabling is an implementation technique that improves the declarativeness and expressiveness of Prolog in dealing with recursion and redundant sub-computations. A critical component in the implementation of an efficient tabling framework is the design of the data structures and algorithms to access and manipulate tabled data. One of the most successful data structures for tabling is tries. In previous work, our initial approach to deal with concurrent table accesses, implemented on top of the Yap Prolog system, was to use lock-based trie data structures. In this work, we propose a new design based on lock-free data structures and, in particular, we focus our discussion on the correctness and efficiency of extending Yap's tabling framework to support lock-free expandable tries. Experimental results show that our new lock-free design can effectively reduce the execution time and scale better, when increasing the number of threads, than the original lock-based design. © 2014 Springer International Publishing.

Abstract
Logic Programming languages, such as Prolog, offer a great potential for the exploitation of implicit parallelism. One of the most noticeable sources of implicit parallelism in Prolog programs is or-parallelism. Or-parallelism arises from the simultaneous evaluation of a subgoal call against the clauses that match that call. Nowadays, multicores and clusters of multicores are becoming the norm and, although, many parallel Prolog systems have been developed in the past, to the best of our knowledge, none of them was specially designed to explore the combination of shared and distributed memory architectures. Conceptually, an or-parallel Prolog system consists of two components: an or-parallel engine (i.e., a set of independent Prolog engines which we named a team of workers) and a scheduler. In this work, we propose a team-based scheduling model to efficiently exploit parallelism between different or-parallel engines running on top of clusters of multicores. Our proposal defines a layered approach where a second-level scheduler specifies a clean interface for scheduling work between the base or-parallel engines, thus enabling different scheduling combinations to be used for distributing work among workers inside a team and among teams.

Abstract
Rational terms or rational trees are terms with one or more infinite sub-terms but with a finite representation. Rational terms appeared as a side effect of omitting the occurs check in the unification of terms, but their support across Prolog systems varies and often fails to provide the expected functionality. A common problem is the lack of support for printing query bindings with rational terms. In this paper, we present a survey discussing the support of rational terms among different Prolog systems and we propose the integration of a Prolog predicate, that works in several existing Prolog systems, in order to overcome the technical problem of printing rational terms. Our rational term printing predicate could be easily adapted to work for the top query printouts, for user printing and for debugging purposes.

Abstract

Abstract

Abstract
Linear Meld is a concurrent forward-chaining linear logic programming language where logical facts can be asserted and retracted in a structured way. The database of facts is partitioned by the nodes of a graph structure which leads to parallelism if nodes are executed simultaneously. Communication arises whenever nodes send facts to other nodes by fact derivation. We present an overview of the virtual machine that we implemented to run Linear Meld on multicores, including code organization, thread management, rule execution and database organization for efficient fact insertion, lookup and deletion. Although our virtual machine is a work-in-progress, our results already show that Linear Meld is not only capable of scaling graph and machine learning programs but it also exhibits some interesting performance results when compared against other programming languages.