Sebastian Schaffert

IkeWiki: A Semantic Wiki for Collaborative Knowledge Management

This article describes the architecture and design principles of IkeWiki, a semantic Wiki we developed at Salzburg research. Outstanding features of IkeWiki are its support for collaborative knowledge engineering, its ease of use, its support for different levels of formalisation ranging from informal texts to formal ontologies, and its sophisticated, interactive user interface. While IkeWiki has been developed primarily as a tool for ontology engineering, it can be used in a variety of application scenarios. We briefly present some of these at the end of the article

Web and semantic web query languages: a survey

A number of techniques have been developed to facilitate powerful data retrieval on the Web and Semantic Web. Three categories of Web query languages can be distinguished, according to the format of the data they can retrieve: XML, RDF and Topic Maps. This article introduces the spectrum of languages falling into these categories and summarises their salient aspects. The languages are introduced using common sample data and query types. Key aspects of the query languages considered are stressed in a conclusion.

Xcerpt and visXcerpt: from pattern-based to visual querying of XML and semistructured data

With the advent of XML as a format for data ex-change and semistructured databases, query languagesfor XML and semistructured data have become in-creasingly popular.Many such query languages, like XPath andXQuery, are navigational in the sense that their vari-able binding paradigm requires the programmer tospecify path navigations through the document (ordata item). In contrast, some other languages – suchas UnQL [1] and Xcerpt [2] – are pattern-based: theirvariable binding paradigm is that of mathematical log-ics, i.e. the programmer specifies patterns (or terms)including variables. Arguably, a pattern-based vari-able binding paradigm makes complex queries mucheasier to specify and to read, thus improving theprogramming efficiency. Sustaining this first claimwith practical examples is one of the objectives of thepresent demonstration.Xcerpt [2] is an experimental pattern-based queryand transformation language for XML and semistruc-tured data. Xcerpt uses patterns both for bindingvariables in query expressions and for reassembling thevariables (bound to data items in query expressions) inso-called construct terms. Arguably, a pattern-baseddocument construction combined with a pattern-basedvariable binding results in a rather intuitive, userfriendly, and programming efficient language. Sustain-ing this second claim is another objective of the presentdemonstration.Xcerpt is experimental in the sense that its purposeis to investigate and test another, non-navigational ap-proach to retrieve data from the Web than that ofthe widespread query languages XPath and XQuery.Nonetheless, Xcerpt has been prototypically imple-

Querying the Web Reconsidered: Design Principles for Versatile Web Query Languages

A decade of experience with research proposals as well as standardized query languages for the conventional Web and the recent emergence of query languages for the Semantic Web call for a reconsideration of design principles for Web and Semantic Web query languages. This chapter first argues that a new generation of versatile Web query languages is needed for solving the challenges posed by the changing Web: We call versatile those query languages able to cope with both Web and Semantic Web data expressed in any (Web or Semantic Web) markup language. This chapter further suggests that well-known referential transparency and novel answer-closedness are essential features of versatile query languages. Indeed, they allow queries to be considered like forms and answers like form-fillings in the spirit of the query-by-example paradigm. This chapter finally suggests that the decentralized and heterogeneous nature of the Web requires incomplete data specifications (or incomplete queries) and incomplete data selections (or incomplete answers); the form-like query can be specified without precise knowledge of the queried data, and answers can be restricted to contain only an excerpt of the queried data.

Reasoning in semantic wikis

Semantic wikis combine the collaborative environment of a classical wiki with features of semantic technologies. Semantic data is used to structure information in the wiki, to improve information access by intelligent search and navigation, and to enable knowledge exchange across applications. Though semantic wikis hardly support complex semantic knowledge and inferencing, we argue that this is not due to a lack of practical use cases. We discuss various tasks for which advanced reasoning is desirable, and identify open challenges for the development of inferencing tools and formalisms. Our goal is to outline concrete options for overcoming current problems, since we believe that many problems in semantic wikis are prototypical for other Semantic Web applications as well. Throughout the paper, we refer to our semantic wiki implementations IkeWiki and Semantic MediaWiki for practical illustration.

Semantic Wikis: Approaches, Applications, and Perspectives

In the decade (2001–2011) that has passed since Semantic Wikis were first proposed, systems have been conceived, developed and used for various purposes. This article aims at giving a comprehensive state-of-the-art overview of the research on Semantic Wikis, stressing what makes them easy to use by a wide and possibly inexperienced audience. This article further describes applications and use cases that have driven the research on Semantic Wikis, software techniques, and architectures that have been proposed for Semantic Wikis. Finally, this article suggests possible ways ahead for further research.

LMF: A Framework for Linked Media

Multimedia is currently underrepresented in the Web of Data. This is due to the lack of integrated means to describe, publish, and interlink multimedia content. This paper presents a framework for the publication of media content and its metadata as Linked Data, the Linked Media Framework (LMF). The LMF enables to store and retrieve content and metadata for media resources and resource fragments in a unified way.

Data Retrieval and Evolution on the (Semantic) Web: A Deductive Approach

To make use of data represented on the Semantic Web, it is necessary to provide languages for Web data retrieval and evolution. This article introduces into the (conventional and Semantic) Web query language Xcerpt and the event and update language XChange, and shows how their deductive capabilities make them well suited for querying, changing and reasoning with data on both the conventional and the Semantic Web. To this aim, small application scenarios are introduced.

An entailment relation for reasoning on the web

Reasoning on the Web is receiving an increasing attention because of emerging fields such as Web adaption and Semantic Web. Indeed, the advanced functionalities striven for in these fields call for reasoning capabilities. Reasoning on the Web, however, is usually done using existing techniques rarely fitting the Web. As a consequence, additional data processing like data conversion from Web formats (e.g. XML or HTML) into some other formats (e.g. classical logic terms and formulas) is often needed and aspects of the Web (e.g. its inherent inconsistency) are neglected. This article first gives requirements for an entailment tuned to reasoning on the Web. Then, it describes how classical logics entailment can be modified so as to enforce these requirements. Finally, it discusses how the proposed entailment can be used in applying logic programming to reasoning on the Web.

A Visual Language for Web Querying and Reasoning

As XML is increasingly being used to represent information on the Web, query and reasoning languages for such data are needed. This article argues that in contrast to the navigational approach taken in particular by XPath and XQuery, a positional approach as used in the language Xcerpt is better suited for a straightforward visual representation. The constructs of the pattern- and rule-based query language Xcerpt are introduced and it is shown how the visual representation visXcerpt renders these constructs to form a visual query language for XML.