On Safe Folding

In [3] a general fold operation has been introduced for definite programs wrt computed answer substitution semantics. It differs from the fold operation defined by Tamaki and Sato in [26,25] because its application does not depend on the transformation history. This paper extends the results in [3] by giving a more powerful sufficient condition for the preservation of computed answer substitutions. Such a condition is meant to deal with the critical case when the atom introduced by folding depends on the clause to which the fold applies. The condition compares the dependency degree between the fonding atom and the folded clause, with the semantic delay between the folding atom and the ones to be folded. The result is also extended to a more general replacement operation, by showing that it can be decomposed into a sequence of definition, general folding and unfolding operations

Normalization by Evaluation with Typed Abstract Syntax

We present a simple way to implement typed abstract syntax for thelambda calculus in Haskell, using phantom types, and we specify normalization by evaluation (i.e., type-directed partial evaluation) to yield thistyped abstract syntax. Proving that normalization by evaluation preserves types and yields normal forms then reduces to type-checking thespecification

Logic programming in the context of multiparadigm programming: the Oz experience

Oz is a multiparadigm language that supports logic programming as one of its major paradigms. A multiparadigm language is designed to support different programming paradigms (logic, functional, constraint, object-oriented, sequential, concurrent, etc.) with equal ease. This article has two goals: to give a tutorial of logic programming in Oz and to show how logic programming fits naturally into the wider context of multiparadigm programming. Our experience shows that there are two classes of problems, which we call algorithmic and search problems, for which logic programming can help formulate practical solutions. Algorithmic problems have known efficient algorithms. Search problems do not have known efficient algorithms but can be solved with search. The Oz support for logic programming targets these two problem classes specifically, using the concepts needed for each. This is in contrast to the Prolog approach, which targets both classes with one set of concepts, which results in less than optimal support for each class. To explain the essential difference between algorithmic and search programs, we define the Oz execution model. This model subsumes both concurrent logic programming (committed-choice-style) and search-based logic programming (Prolog-style). Instead of Horn clause syntax, Oz has a simple, fully compositional, higher-order syntax that accommodates the abilities of the language. We conclude with lessons learned from this work, a brief history of Oz, and many entry points into the Oz literature.Comment: 48 pages, to appear in the journal "Theory and Practice of Logic Programming

Programming Languages for Distributed Computing Systems

When distributed systems first appeared, they were programmed in traditional sequential languages, usually with the addition of a few library procedures for sending and receiving messages. As distributed applications became more commonplace and more sophisticated, this ad hoc approach became less satisfactory. Researchers all over the world began designing new programming languages specifically for implementing distributed applications. These languages and their history, their underlying principles, their design, and their use are the subject of this paper. We begin by giving our view of what a distributed system is, illustrating with examples to avoid confusion on this important and controversial point. We then describe the three main characteristics that distinguish distributed programming languages from traditional sequential languages, namely, how they deal with parallelism, communication, and partial failures. Finally, we discuss 15 representative distributed languages to give the flavor of each. These examples include languages based on message passing, rendezvous, remote procedure call, objects, and atomic transactions, as well as functional languages, logic languages, and distributed data structure languages. The paper concludes with a comprehensive bibliography listing over 200 papers on nearly 100 distributed programming languages

Harmonizing CMMI-DEV 1.2 and XP Method to Improve The Software Development Processes in Small Software Development Firms

Most software development organizations are small firms, and they have realized the need to manage and improve their software development and management activities. Traditional Software Process Improvement (SPI) models and standards are not realistic for these firms because of high cost, limited resources and strict project deadlines. Therefore, these firms need a lightweight software development method and an appropriate SPI model to manage and improve their software development and management processes. This study aims to construct a suitable software development process improvement framework for Small Software Development Firms (SSDFs) based on eXtreme Programming (XP) method and Capability Maturity Model Integration for Development Version 1.2 (CMMI-Dev1.2) model. Four stages are involved in developing the framework: (1) aligning XP practices to the specific goals of CMMI-Dev1.2 Key Process Areas (KPAs); (2) developing the proposed software development process improvement framework based on extending XP method by adapting the Extension-Based Approach (EBA), CMMI-Dev1.2, and generic elements of the SPI framework; (3) verifying the compatibility of the proposed framework to the KPAs of CMMI-Dev1.2 by using focus group method coupled with Delphi technique; and (4) validating the modified framework by using CMMI-Dev1.2 questionnaire as a main item to validate the suitability of the modified framework for SSDFs, and conducting two case studies to validate the applicability and effectiveness of this framework for these firms. The result of aligning XP practices to the KPAs of CMMI-Dev1.2 shows that twelve KPAs are largely supported by XP practices, eight KPAs are partially supported by XP practices, and two KPAs are not-supported by XP practices. The main contributions of this study are: software development process improvement framework for SSDFs, elicit better understanding of how to construct the framework, and quality improvement of the software development processes. There are possible avenues for extending this research to fulfil the missing specific practices of several KPAs, examining other agile practices and using CMMI-Dev1.3 to improve the framework, and conducting more case studie