The Web-Based Systems Group explores technical and economic questions concerning the development of global, decentralized information environments.

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Current information about our work is found at


This pages gives an overview about our open source software projects, community projects and about information resources that we maintain.

Group Members

Open Source Software Projects

We initialized and maintain the following open source software projects:

1. RAP - RDF API for PHP

RAP is a leading Semantic Web toolkit for PHP developers. It offers features for parsing, manipulating, storing, querying, serving, and serializing RDF graphs. RAP was started in 2002 and has been extended with various code contributions from the Semantic Web community. Its latest release (V0.9.4) includes among others: different APIs for manipulating RDF graphs, RDF/XML, Turtle and GRDDL parsers, in-memory or database model storage, an inference engine, an integrated RDF server, and support for the SPARQL query language. Project homepage
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2. D2R Server - Publishing Relational Databases on the Semantic Web

D2R Server is a tool for publishing relational databases on the Semantic Web. The server enables RDF and HTML browsers to navigate the content of non-RDF databases, and allows applications to query the database using the SPARQL query language. Project homepage
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3. D2RQ - Treating Non-RDF Databases as Virtual RDF Graphs

As Semantic Web technologies are getting mature, there is a growing need for RDF applications to access the content of non-RDF, legacy databases without having to replicate the whole database into RDF. D2RQ is a declarative language to describe mappings between relational database schemata and OWL/RDFS ontologies. The mappings allow RDF applications to access the content of huge, non-RDF databases using Semantic Web query languages like SPARQL. Project homepage
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4. Semantic Web Client Library

The Sematic Web Client Library represents the complete Semantic Web as a single RDF graph. The library enables applications to query this global graph using SPARQL- and find(SPO) queries. To answer queries, the library dynamically retrieves information from the Semantic Web by dereferencing HTTP URIs and by following rdfs:seeAlso links. The library is written in Java and is based on the Jena framework. Project homepage
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5. NG4J - Named Graphs API for Jena

NG4J - Named Graphs API for Jena is a software toolkit for creating, manipulating, persisting, and exchanging sets of Named Graphs . Graph sets can be stored in memory or in a relational database. The API provides parsers and serializers for the TriX, TriG and RDF/XML syntaxes and allows graph sets to be signed using the Semantic Web Publishing vocabulary . Project homepage
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6. Disco - Hyperdata Browser

The Disco - Hyperdata Browser is a simple browser for navigating the Semantic Web as an unbound set of data sources. The browser renders all information, that it can find on the Semantic Web about a specific resource, as an HTML page. This resource description contains hyperlinks that allow you to navigate between resources. While you move from resource to resource, the browser dynamically retrieves information by dereferencing HTTP URIs and by following rdfs:seeAlso links . Project homepage
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7. WIQA - Information Quality Assessment enabled Semantic Web Browser

The WIQA browser is a general purpose RDF browser that supports users in exploring RDF datasets containing information from multiple sources. Information can be filtered using a wide range of different, user-definable information quality assessment policies. In order to facilitate the user's understanding of the filtering decisions, the browser can create explanations why displayed information fulfils a selected policy . Project homepage
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8. WIQA - Information Quality Assessment Framework

Information providers on the Web have different levels of knowledge, different views of the world and different intensions. Thus, provided information may be wrong, biased, inconsistent or outdated. Before information from the Web is used to accomplish a specific task, its quality should be assessed according to task-specific criteria. The WIQA - Information Quality Assessment Framework is a set of software components that empowers information consumers to employ a wide range of different information quality assessment policies to filter information from the Web. Project homepage
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9. SemMF: Semantic Matching Framework

SemMF is an easy-to-use flexible framework for calculating semantic similarity between objects represented as arbitrary RDF Graphs, based on similarities of specified properties. The framework can be used in semantic web applications working with RDF graphs containing concepts drawn from both a flat and a hierarchical domain making it applicable in a wide range of different use cases. The user is given the choice to apply either hierarchical or non-hierarchical concept matching techniques for different kinds of object properties. Project homepage
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Community Projects

We participate in the following community projects:

1. is a community effort to extract structured information from Wikipedia and to make this information available on the Web. dbpedia allows you to ask sophisticated queries against Wikipedia and to link other datasets on the Web to Wikipedia data. Project homepage

2. Linking Open Data

W3C Semantic Web Education and Outreach project that aims at interlinking data from different open access data sources like Wikipedia, Geonames and Muscibrainz. Project homepage


Information Resources

We publish and maintain the following information resources:

1. Developers Guide to Semantic Web Toolkits for different Programming Languages

The guide collects links to Semantic Web toolkits for different programming languages and gives an overview about the features of each toolkit, the strength of the development effort and the toolkit's user community. Project homepage

2. Semantic Web Trust and Security Resource Guide

The security, trust, information quality and privacy issues arising from the vision of the Semantic Web as a global information integration infrastructure are mainly unsolved. The resource guide collects papers, ontologies, schemata and standards that might be building blocks for the future Semantic Web trust layer. Project homepage

3. D2R Server publishing the DBLP Bibliographic Database

We run a D2R Server publishing the DBLP Bibliography Database as linked data on the Semantic Web . The database can be accessed using your plain old web browser, Semantic Web browsers, SPARQL query clients. The DBLP database provides bibliographic information on major computer science journals and conference proceedings. The database contains more than 800.000 articles and 400.000 authors . The complete RDF view on the database consists of approximately 15 million RDF triples. Project homepage

4. RDF Book Mashup

The RDF book mashup demonstrates how Web 2.0 data sources like Amazon, Google or Yahoo can be integrated into the Semantic Web. The RDF book mashup makes information about books, their authors, reviews, and online bookstores available on the Semantic Web. This information can be used by RDF tools and you can link to it from your own Semantic Web data. Altogether the book mashup published around a billion RDF triples on the Semantic Web (rough estimate). Project homepage