Veronica Dahl

Computational Logic — CL 2000

Syntax for Variable Binders: An Overview . . . . . . . . . . . . . . . . . . . . 239 Dale Miller Goal-Directed Proof Search in Multiple-Conclusioned Intuitionistic Logic . . 254 James Harland, Tatjana Lutovac, and Michael Winikoff Efficient EM Learning with Tabulation for Parameterized Logic Programs . 269 Yoshitaka Kameya and Taisuke Sato Model Generation Theorem Proving with Finite Interval Constraints . . . . . 285 Reiner Hähnle, Ryuzo Hasegawa, and Yasuyuki Shirai Combining Mobile Processes and Declarative Programming . . . . . . . . . . . . . 300 Rachid Echahed and Wendelin Serwe

On database systems development through logic

The use of logic as a single tool for formalizing and implementing different aspects of database systems in a uniform manner is discussed. The discussion focuses on relational databases with deductive capabilities and very high-level querying and defining features. The computational interpretation of logic is briefly reviewed, and then several pros and cons concerning the description of data, programs, queries, and language parser in terms of logic programs are examined. The inadequacies are discussed, and it is shown that they can be overcome by the introduction of convenient extensions into logic programming. Finally, an experimental database query system with a natural language front end, implemented in PROLOG, is presented as an illustration of these concepts. A description of the latter from the users point of view and a sample consultation session in Spanish are included.

HYPROLOG: a new logic programming language with assumptions and abduction

We present HYPROLOG, a novel integration of Prolog with assumptions and abduction which is implemented in and partly borrows syntax from Constraint Handling Rules (CHR) for integrity constraints. Assumptions are a mechanism inspired by linear logic and taken over from Assumption Grammars. The language shows a novel flexibility in the interaction between the different paradigms, including all additional built-in predicates and constraints solvers that may be available. Assumptions and abduction are especially useful for language processing, and we can show how HYPROLOG works seamlessly together with the grammar notation provided by the underlying Prolog system. An operational semantics is given which complies with standard declarative semantics for the “pure” sublanguages, while for the full HYPROLOG language, it must be taken as definition. The implementation is straightforward and seems to provide for abduction, the most efficient of known implementations; the price, however, is a limited use of negations. The main difference wrt. previous implementations of abduction is that we avoid any level of metainterpretation by having Prolog execute the deductive steps directly and by treating abducibles (and assumptions as well) as CHR constraints.

Discontinuous grammars

This article ties together previously scattered research on discontinuous grammars—logic grammars in which non‐explicit sequences of symbols can be alluded to in the rules and sometimes repositioned by them. After an introduction, we define them formally, present their background, and provide intuitive insight into their use. Next, we examine several motivating arguments, from both formal and natural language processing viewpoints, and we discuss the static discontinuity family of these grammars, in which (a) the nonexplicit strings are not allowed to move and (b) linguistic constraints specifically designed to suit, in particular, Government and Binding theory can be defined modularly and statically in terms of node domination in parse trees and are enforced dynamically. Finally, we discuss implementation issues, related work, and extensions.

LogiMOO: An extensible multi-user virtual world with natural language control

Abstract LogiMOO is a BinProlog-based Virtual World running under Netscape and Internet Explorer for distributed group-work over the INTERNET and user-crafted virtual places, virtual objects and agents. LogiMOO is implemented on top of a multi-threaded blackboard-based logic programming system (BinProlog) featuring Linda-style coordination. Remote and local blackboards support transparent distribution of data and processing over TCP/IP links, while threads ensure high-performance local client-server dynamics. Embedding in Netscape provides advanced VRML and HTML frame-based navigation and multi-media support, while LogiMOO handles virtual presence and acts as a very high-level multi-media object broker. User-friendliness is achieved through a controlled English interface written in terms of Assumption Grammars. Its language coverage is extensible in that the user can incorporate new nouns, verbs and adjectives as needed by changes in the world. Immediate evaluation of world knowledge by the parser yields representations which minimize the unknowns allowing us to deal with advanced Natural Language constructs like anaphora and relativization efficiently. We take advantage of the simplicity of our controlled language to provide as well an easy adaptation to other natural languages than English, with English-like representations as a universal interlingua.

Meaning in context

A model for context-dependent natural language semantics is proposed and formalized in terms of possible worlds. The meaning of a sentence depends on context and at the same time affects that context representing the knowledge about the world collected from a discourse. The model fits well with a “flat” semantic representation as first proposed by Hobbs (1985), consisting basically of a conjunction of atomic predications in which all variables are existentially quantified with the widest possible scope; in our framework, this provides very concise semantic terms as compared with other representations. There is a natural correspondence between the possible worlds semantics and a constraint solver, and it is shown how such a semantics can be defined using the programming language of Constraint Handling Rules (Fruhwirth, 1995). Discourse analysis is clearly a process of abduction in this framework, and it is shown that the mentioned constraint solvers serve as effective and efficient abductive engines for the purpose.

High-level networking with mobile code and first order AND-continuations

We describe a scheme for moving living code between a set of distributed processes coordinated with unification based Linda operations, and its application to building a comprehensive Logic programming based Internet programming framework. Mobile threads are implemented by capturing first order continuations in a compact data structure sent over the network. Code is fetched lazily from its original base turned into a server as the continuation executes at the remote site. Our code migration techniques, in combination with a dynamic recompilation scheme, ensure that heavily used code moves up smoothly on a speed hierarchy while volatile dynamic code is kept in a quickly updatable form. Among the examples, we describe how to build programmable client and server components (Web servers, in particular) and mobile agents.

Backtrackable State with Linear Affine Implication and Assumption Grammars

A general framework of handling state information for logic programming languages on top of backtrackable assumptions (linear affine and intuitionistic implications ranging over the current continuation) is introduced. Assumption Grammars (AGs), a variant of Extended DCGs handling multiple streams without the need of a preprocessing technique, are specified within our framework. Equivalence with DCGs is shown through a translation from AGs to DCGs and through use of an implementation-independent meta-interpreter, customized for handling both DCGs and AGs.

A logic programming infrastructure for remote execution, mobile code and agents

We describe a set of programming patterns used for implementing a scalable infrastructure which supports remote execution mechanisms, mobile code and agents in a distributed logic programming framework. The particular focus of this paper is on the use of BinPrologs strong metaprogramming abilities. Some advanced logic programming constructs as intuitionistic implication, high-order call/N cooperate with encapsulated socket-level constructs for maximum configurability and efficiency. We show that strong metaprogramming is not a security threat if used through a set of filtering interactors which allow source level implementation of arbitrary security policies. Mobile code is implemented in a scalable way through a set of distributed client+server pairs interconnected through a master server acting only as an address exchange broker for peer-to-peer interactors. We have thoroughly tested our programming patterns and design principles through a realistic implementation in a widely used, freely available Prolog system (http://clement.info.umoncton.ca/BinProlog) as well as with its Java peers built on top of our unification enhanced Java based Linda implementation (http://clement.info.umoncton.ca/LindaInteractor).

Efficient algorithms for the discovery of DNA oligonucleotide barcodes from sequence databases.

Efficient design of barcode oligonucleotides can lead to significant cost reductions in the manufacturing of DNA arrays. Previous methods are based on either a preliminary alignment, which reduces their efficiency for intron‐rich regions, or on a brute force approach, not feasible for large‐scale problems or on data structures with very poor performance in the worst case. One of the algorithms we propose uses ‘oligonucleotide sorting’ for the discovery of oligonucleotide barcodes of given sizes, with good asymptotic performance. Specific barcode oligonucleotides with at least one base difference from other sequences in a database are found for each individual sequence. With another algorithm, specific oligonucleotides can also be found for groups or clades in the database, which have 100% homology for all oligonucleotide sequences within the group or clade while having differences with the rest of the data. By re‐organizing the sequences/groups in the database, oligonucleotides for different hierarchical levels can be found. The oligonucleotides or polymorphism locations identified as species or clade specific by the new algorithm are refined and screened further for hybridization thermodynamic properties with third party software.