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The World Wide Web as an application platform becomes increasingly important. However, the development of Web applications is often more complex than for the desktop. Web-based development environments like Lively Webwerkstatt can mitigate this problem by making the development process more interactive and direct. By moving the development environment into the Web, applications can be developed collaboratively in a Wiki-like manner. This report documents the results of the project seminar on Web-based Development Environments 2010. In this seminar, participants extended the Web-based development environment Lively Webwerkstatt. They worked in small teams on current research topics from the field of Web-development and tool support for programmers and implemented their results in the Webwerkstatt environment. / Das World Wide Web wird immer mehr zu einer Anwendungsplattform. Die Entwicklung von Web-Applikationen ist jedoch oft komplexer als die Erstellung traditioneller Desktop-Anwendungen. Web-basierte Entwicklungsumgebungen wie LivelyWebwerkstatt vereinfachen das Entwickeln, da der Programmierprozess interaktiver und direkter wird. Zudem ist es möglich, dass ähnlich wie in einem Wiki Entwickler bei der Anwendungserstellung zusammenarbeiten. Dieser Bericht dokumentiert die Ergebnisse des Projektseminars Web-basierte Entwicklungsumgebungen 2010. Im Rahmen des Seminars haben sich die Teilnehmer mit aktuellen Fragen aus dem Bereich derWeb-Entwicklung undWerkzeugunterstützung für Programmierer beschäftigt und die bestehende Web-basierte Entwicklungsumgebung Lively Webwerkstatt entsprechend erweitert.

Versionsverwaltungssysteme (VCS) ermöglichen es Entwicklern, Änderungen an Softwareartifakten zu verwalten. VCS werden mit Hilfe einer Vielzahl verschiedener Werkzeuge bedient, wie z.,B. graphische Front-ends oder Kommandozeilenwerkzeuge. Es ist wünschenswert mit einzelnen solcher Werkzeuge unterschiedliche VCS bedienen zu können. Bislang hat sich jedoch keine Abstraktion für Versionsverwaltungssysteme durchgesetzt, mit deren Hilfe solche Werkzeuge erstellt werden können. Stattdessen implementieren Werkzeuge zur Interaktion mit mehreren VCS ad-hoc Lösungen. Diese Masterarbeit stellt Pur vor, eine Abstraktion über Versionsverwaltungskonzepte. Mit Hilfe von Pur können Anwendungsprogramme entwickelt werden, die mit mehreren Versionsverwaltungssystemen interagieren können. Im Rahmen dieser Arbeit wird eine Implementierung dieser Abstraktion bereitgestellt und mit Hilfe eines Anwendungsprogramms validiert. / Version Control Systems (VCS) allow developers to manage changes to software artifacts. Developers interact with VCSs through a variety of client programs, such as graphical front-ends or command line tools. It is desirable to use the same version control client program against different VCSs. Unfortunately, no established abstraction over VCS concepts exists. Instead, VCS client programs implement ad-hoc solutions to support interaction with multiple VCSs. This thesis presents Pur, an abstraction over version control concepts that allows building rich client programs that can interact with multiple VCSs. We provide an implementation of this abstraction and validate it by implementing a client application.

A constraint programming system combines two essential components: a constraint solver and a search engine. The constraint solver reasons about satisfiability of conjunctions of constraints, and the search engine controls the search for solutions by iteratively exploring a disjunctive search tree defined by the constraint program. The Monadic Constraint Programming framework gives a monadic definition of constraint programming where the solver is defined as a monad threaded through the monadic search tree. Search and search strategies can then be defined as firstclass objects that can themselves be built or extended by composable search transformers. Search transformers give a powerful and unifying approach to viewing search in constraint programming, and the resulting constraint programming system is first class and extremely flexible.

In this talk, I would like to share my experiences gained from participating in four CSP solver competitions and the second ASP solver competition. In particular, I’ll talk about how various programming techniques can make huge differences in solving some of the benchmark problems used in the competitions. These techniques include global constraints, table constraints, and problem-specific propagators and labeling strategies for selecting variables and values. I’ll present these techniques with experimental results from B-Prolog and other CLP(FD) systems.

We describe a framework to support the implementation of web-based systems to manipulate data stored in relational databases. Since the conceptual model of a relational database is often specified as an entity-relationship (ER) model, we propose to use the ER model to generate a complete implementation in the declarative programming language Curry. This implementation contains operations to create and manipulate entities of the data model, supports authentication, authorization, session handling, and the composition of individual operations to user processes. Furthermore and most important, the implementation ensures the consistency of the database w.r.t. the data dependencies specified in the ER model, i.e., updates initiated by the user cannot lead to an inconsistent state of the database. In order to generate a high-level declarative implementation that can be easily adapted to individual customer requirements, the framework exploits previous works on declarative database programming and web user interface construction in Curry.

We introduce a simple approach extending the input language of Answer Set Programming (ASP) systems by multi-valued propositions. Our approach is implemented as a (prototypical) preprocessor translating logic programs with multi-valued propositions into logic programs with Boolean propositions only. Our translation is modular and heavily benefits from the expressive input language of ASP. The resulting approach, along with its implementation, allows for solving interesting constraint satisfaction problems in ASP, showing a good performance.

In this paper we consider a simple syntactic extension of Answer Set Programming (ASP) for dealing with (nested) existential quantifiers and double negation in the rule bodies, in a close way to the recent proposal RASPL-1. The semantics for this extension just resorts to Equilibrium Logic (or, equivalently, to the General Theory of Stable Models), which provides a logic-programming interpretation for any arbitrary theory in the syntax of Predicate Calculus. We present a translation of this syntactic class into standard logic programs with variables (either disjunctive or normal, depending on the input rule heads), as those allowed by current ASP solvers. The translation relies on the introduction of auxiliary predicates and the main result shows that it preserves strong equivalence modulo the original signature.

We present the tool Kato which is, to the best of our knowledge, the first tool for plagiarism detection that is directly tailored for answer-set programming (ASP). Kato aims at finding similarities between (segments of) logic programs to help detecting cases of plagiarism. Currently, the tool is realised for DLV programs but it is designed to handle various logic-programming syntax versions. We review basic features and the underlying methodology of the tool.