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Eclipse Logic Framework (ELF)


Eclipse Logic Framework (ELF) is a proposed open source project under the Eclipse Technology Project.

This proposal is in the Project Proposal Phase (as defined in the Eclipse Development Process document) and is written to declare its intent and scope. This proposal is written to solicit additional participation and input from the Eclipse community. You are invited to comment on and/or join the project. Please send all feedback to the ELF forum.


Prolog (PROgramming LOGic) was developed in 1972 (although sources vary) by Alain Colmerauer and Phillipe Roussel, both of University of Aix-Marseille, France, in collaboration with Robert Kowalski of the University of Edinburgh, United Kingdom. While popular in the Artificial Intelligence community, which used it amongst other things for the development of expert systems and natural language processing, its significance has waxed and waned over time. Even though the language has been ISO standardized in 1995, it has never broken through in the computer industry in the way other languages have, especially when compared to the now ubiquitous Java, developed by James Gosling at Sun Microsystems and released in 1995.

In 1996, Bart Demoen of the Katholieke Universiteit Leuven, Belgium, and Paul Tarau, at that time at the Université de Moncton, Canada, outlined a method to run Prolog programs on a Java virtual machine. A limited proof-of-concept implementation was made available under the moniker 'jProlog'. The idea was picked up again soon after by Mutsunori Banbara and Naoyuki Tamura of Kobe University, Japan, and developed into a feature-complete clean-room implementation under the moniker 'Prolog Cafe' (, of which the last update dates June 24th 2009.

In 2002, Tobias Rho created the ‘Prolog Development Tool’ (PDT), the first Eclipse-based IDE for working with SWI-Prolog, as part of his diploma thesis at the University of Bonn. Since then the PDT project has continuously evolved in its academic environment, led by Dr. Günter Kniesel, with contributions of Tobias Rho, Lukas Degener and Eva Stöwe. The PDT will be subsumed by the ELF, but for now the original project can still be found at

With the advent of the Semantic Web, a new spin was put on the A.I. research accomplishments of the last 50 years. While Tim Berners Lee contended in 1998 that a Semantic Web is not Artificial Intelligence, he did call it a 'language of logic'. Logic languages were designed with the specific purpose of making the expression of the solution to problems straightforward. Yet, Semantic Technologies are developed using popular contemporary languages, all of which are notoriously ill-suited for that very same purpose. Equally true, those (early) logic languages have become sidelined because they made many real-world everyday-programming tasks cumbersome.

The ELF represents a renewed interest in the pursuit of practical logic programming.


The Eclipse Logic Framework project will provide a complete Prolog development and run-time environment, adding Prolog to the existing Eclipse ecosystem of supported languages:

  • The IDE will support editing, code navigation and refactoring of Prolog code. It will be configurable to support external native Prolog run-time engines (such as SWI-Prolog) and the project's own internal run-time.
  • The internal run-time will allow running Prolog programs on the Java Virtual Machine, providing the basis for a seamless integration of Prolog and Java in a multi-paradigm approach that lets developers use the best of each language for each particular task.

As a platform, the ELF will provide the means to integrate with results from specific areas of research into the Prolog language. It will invite researchers and tool makers from the logic programming and multi-paradigm programming community to actively contribute to the development and critical evaluation of the project.

Value Proposition

Industrial: While the ELF project recognizes its academic origins, the emphasis is on the development of an industry-grade, production-ready product. The project is aimed at developers and researchers who can benefit from logic programming solutions in general. Beyond that, it will provide a unique platform for novel families of logic-based applications that can take advantage from running on a Java virtual machine. The project provides complete support for the Equinox OSGi framework and Google App Engine for Java (GAE/J).

Educational: Because it offers an all-in-one Prolog IDE, the ELF has the potential to become the tool-of-choice for educational purposes. It lowers the barrier for entry into the realm of logic programming. By supporting multiple run-times out-of-the-box, teachers and students will be able to focus on the language issues, as opposed to the installation issues.

Semantic: The ELF will increase the presence of the Eclipse community at the Semantic Technologies frontier and will leverage development of Semantic Web applications on the Java platform. It will prove especially relevant in the area of 'Logic Frameworks' in the Semantic Web Technology Stack.

Proposed Components

The project's initial target is the introduction of the following components:

  1. a set of IDE contributions to edit Prolog source files which meet the expected standards of well-known, existing Eclipse IDE projects,
  2. a connector framework to interact with native Prolog run-time engines and interpreters,
  3. a Java-based Prolog interpreter, which runs without the need of a native Prolog run-time environment,
  4. a Prolog-to-Java source-to-source translator system,
  5. a high-performance Java-based Prolog run-time,
  6. a 'Java Architecture for Prolog Binding' (JAPB) API to facilitate integration with pure Java programs,
  7. a set of built-in example projects.

Beyond the scope of the initial target, the following components are under consideration:

  • support for Common Logic (CL) data formats: the Import Common Logic Interchange Format (CLIF), for the Conceptual Graph Interchange Format (CGIF) and the XML-based notation for Common Logic (XCL),
  • support for Semantic Web data formats: the Resource Description Framework (RDF) and the Ontology Web Language (OWL).

Relationship with other Eclipse Projects

The Eclipse Logic Framework project will be built on top of the Eclipse IDE. Although the Prolog IDE will stand on its own, the Java-specific hybrid language aspects of the ELF will depend on JDT components in order to function.

This project has the potential to leverage the 'Eclipse IDE For Education' (IDE4EDU) project, by providing a Prolog IDE and run-time announced but unavailable at the time of this writing.


This project requests a place in the Eclipse Tools hierarchy as it facilitates programming in Prolog, and Java in combination with Prolog.

While the main driver is a commercial entity, the product shall remain absolutely free and without restrictions. In addition, this project will strive to develop a working relationship with the academic world, and where possible, integrate existing and ongoing development efforts of academic origins.


Proposed initial committers:

  • TOMOTON N.V., Belgium - Dann Martens (Project Lead)
  • Bonn University, Germany - Günter Kniesel (Project Lead)
  • Bonn University, Germany – Tobias Rho
  • Bonn University, Germany – Eva Stöwe

Interested parties

The following academic institutions have expressed interest in this project. Key contacts listed.

  • Kobe University, Japan - Mutsunori Banbara
  • Kobe University, Japan - Naoyuki Tamura
  • Eclipse IDE for Education
  • Dwight Duego

Code Contributions

The Kobe University, Japan, has contributed the Prolog-to-Java source-to-source translator system. The individual contributors involved in the development of the original code base were Mutsunori Banbara and Naoyuki Tamura.

Bonn University, Germany, has contributed the Prolog IDE and parts, from the externally hosted Prolog Development Tools (PDT) project. The code base was originally licensed under the Eclipse Public License. The individual contributors involved in the development of the original code base were Lukas Degener, Tobias Rho, Eva Stöwe and Frank Mühlschlegel.

TOMOTON, NV, Belgium, has requested the Kobe University to dual licence the translator system under the Eclipse License, next to the GNU General Public License as published by the Free Software Foundation (version 2 of the License). In addition, TOMOTON has modified the existing code base to allow the run-time to work both in an OSGi container, as well as in the sandbox of Google App Engine for Java. TOMOTON NV has designed and developed the JAPB API. The individual contributor involved in the modification and separate development was Dann Martens.

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