Abstract Processing programs as data is one of the successes of functional and logic programming. Higher-order functions, as program-processing programs are called in functional programming, and meta-programs, as they are called in logic programming, are widespread declarative programming techniques. In logic programming, there is a gap between the meta-programming practice and its theory: The formalizations of meta-programming do not explicitly address its impredicativity and are not fully adequate. This article aims at overcoming this unsatisfactory situation by discussing the relevance of impredicativity to meta-programming, by revisiting former formalizations of meta-programming, and by defining Reflective Predicate Logic, a conservative extension of first-order logic, which provides a simple formalization of meta-programming.

Nudging students to a better learning is a common practice among teachers of small classes which is impossible in large classes. Indeed, no teacher has enough time for giving individual feedback to several tens or hundred students, let alone be sufficiently aware of the progress and difficulties of each of them. This article reports on a case study using computed individual predictions for sustaining the motivation of large class’ audiences thus nudging them to a better learning. More precisely, this article reports on a case study in which students are given individual predictions of their withdrawal, or “skipping”, and examination performances with the aim of increasing their participation to classes and to homework. A real-life evaluation of the approach in a computer sicence course points to both its effectiveness and its positive reception by students.

Decision making is typically a well-defined process. The decision is formulated, the decision options are determined and information regarding the options is retrieved by the decision makers. Eventually, the decision is taken by some kind of voting. In this article we propose a novel approach to decision making called liquid decision making (LDM). LDM enables people to incorporate new information, to react to the voting of others, and to reconsider and revise their own voting. Additionally, a competitive element is introduced by basing the decision making mechanism on market principles: Indecision can lead to a loss of influence in the decision making. Artificial market perturbations are used to gauge the stability of a decision suggested by a market equilibrium. This article introduces LDM and its market perturbations and reports on an exploratory study conducted using LDM.

Web crawlers are increasingly used for focused tasks such as the extraction of data from Wikipedia or the analysis of social networks like last.fm. In these cases, pages are far more uniformly structured than in the general Web and thus crawlers can use the structure of Web pages for more precise data extraction and more expressive analysis.

KiWi is a semantic Wiki that combines the Wiki philosophy of collaborative content creation with the methods of the Semantic Web in order to enable effective knowledge management.

Studies agree that searchers are often not satisfied with the performance of current enterprise search engines. As a consequence, more scientists worldwide are actively investigating new avenues for searching to improve retrieval performance. This paper contributes to YASA (Your Adaptive Search Agent), a fully implemented and thoroughly evaluated ontology-based information retrieval system for the enterprise. A salient particularity of YASA is that large parts of the ontology are automatically filled with facts by recycling and transforming existing data. YASA offers context-based personalization, faceted navigation, as well as semantic search capabilities. YASA has been deployed and evaluated in the pharmaceutical research department of Roche, Penzberg, and results show that already semantically simple ontologies suffice to considerably improve search performance.

In the domain of supervisory control and data acquisition (SCADA), significant challenges reside in the variety of proprietary interfaces and protocols which accompany the components and devices provided by different manufacturers. The Facility Control Markup Language (FCML) is designed to provide standardized and uniform access to different devices which usually only adhere to proprietary interfaces and protocols. As an application of the Extensible Markup Language (XML), FCML is designed as an open and extensible standard which can easily be adapted and extended to include requirements of future applications and devices. The subjacent vision includes the conjecture that Web-based SCADA systems are very promising for a wide range of SCADA applications, for reasons of modularity and ease of deployment.

Many data sources on the Web evolve: they change their content over time, typically as reactions to events. Such changes often need to be mirrored in data on other Web nodes: updates need to be propagated. To respond to the need for evolution and reactivity both locally and globally, the language XChange has been developed. We demonstrate its applicability in a concrete scenario of distributed Web sites of a scientific community with mutual data dependencies.

Applications and services that access Web data are becoming increasingly more useful and wide-spread. Current main-stream Web query languages such as XQuery, XSLT, or SPARQL, however, focus only on one of the different data formats available on the Web. In contrast, Xcerpt is a emphversatile semi-structured query language, i.e., a query language able to access all kinds of Web data such as XML and RDF in the same language reusing common concepts and language constructs. To integrate heterogeneous data and as a foundation for Semantic Web reasoning, Xcerpt also provides rules. Xcerpt has a visual companion language, visXcerpt, that is conceived as a mere rendering of the (textual) query language Xcerpt using a slightly extended CSS. Both languages are demonstrated along a realistic use case integrating XML and RDF data highlighting interesting and unique features. Novel language constructs and optimization techniques are currently under investigation in the Xcerpt project ([email protected] urlhttp://xcerpt.org/).

Data streams are an emerging technology for data dissemination in cases where the data throughput or size makes it unfeasible to rely on the conventional approach based on storing the data before processing it. SPEX evaluates XPath queries against XML data streams. SPEX is built upon formal frameworks for (1) rewriting XPath queries into equivalent XPath queries without reverse axes and (2) correct query evaluation with polynomial combined complexity using networks of pushdown transducers. Such transducers are simple, independent, and can be connected in a flexible manner, thus allowing not only easy extensions but also extensive query optimization. Querying XML streams with SPEX consists in four steps: first, the input XPath query is rewritten into an XPath query without reverse axes. Second, the forward XPath query is compiled into a logical query plan abstracting out details of the concrete XPath syntax. Then, a physical query plan is generated by extending the logical query plan with operators for determination and collection of answers. In the last step, the XML stream is processed continuously with the physical query plan, and the output stream conveying the answers to the original query is generated progressively.

Data referring to cultural calendars such as the widespread Gregorian dates but also dates after the Chinese, Hebrew, or Islamic calendars as well as data referring to professional calendars like fiscal years or teaching terms are omnipresent on the Web. Formalisms such as XML Schema have acknowledged this by offering a rather extensive set of Gregorian dates and times as basic data types. This article introduces into CaTTS, the Calendar and Time Type System. CaTTS goes far beyond predefined date and time types after the Gregorian calendar as supported by XML Schema. CaTTS first gives rise to declaratively specify more or less complex cultural or professional calendars including specificities such as leap seconds, leap years, and time zones. CaTTS further offers a tool for the static type checking (of data typed after calendar(s) defined in CaTTS). CaTTS finally offers a language for declaratively expressing and a solver for efficiently solving temporal constraints (referring to calendar(s) expressed in CaTTS). CaTTS complements data modeling and reasoning methods designed for generic Semantic Web applications such as RDF or OWL with methods specific to the particular application domain of calendars and time.

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.

Rooted in electronic publishing, XML is now widely used for modelling and storing structured text documents. Especially in the WWW, retrieval of XML documents is most useful in combination with a relevance-based ranking of the query result. Index structures with ranking support are therefore needed for fast access to relevant parts of large document collections. This paper proposes a classification scheme for both XML ranking models and index structures, allowing to determine which index suits which ranking model. An analysis reveals that ranking parameters related to both the content and structure of the data are poorly supported by most known XML indices. The IR-CADG index, owing to its tight integration of content and structure, supports various XML ranking models in a very efficient retrieval process. Experiments show that it outperforms separate content/structure indexing by more than two orders of magnitude for large corpora of several hundred MB.

This paper describes (eXploring XML data), a system for efficiently querying XML data and visually exploring answer sets, with a special focus on the novel user interface for interaction with the query result. The process of querying XML documents is performed interactively and in a completely graphical manner. Special attention was paid to simplicity of the user interface: In a first step the user submits a query to the system and gets the result presented in the form of a Complete Answer Aggregate (CAA). CAAs visually (re)present the answer space in a compact form and thus provide a good overview over the set of all answers. They offer a rich variety of presentation modes and exploration techniques which are used in the second step to interactively explore the answer space.

We present SPEX, a streamed and progressive evaluation of regular path expressions with XPath-like qualifiers against XML streams. SPEX proceeds as follows. An expression is translated in linear time into a network of transducers, most of them having 1-DPDT equivalents. Every stream message is then processed once by the entire network and result fragments are output on the fly. In most practical cases SPEX needs a time linear in the stream size and for transducer stacks a memory quadratic in the stream depth. Experiments with a prototype implementation point to a very good efficiency of the SPEX approach.

The features of logic programming that seem unconventional from the viewpoint of classical logic can be explained in terms of constructivistic logic. We motivate and propose a constructivistic proof theory of non-Horn logic programming. Then, we apply this formalization for establishing results of practical interest. First, we show that 'stratification' can be motivated in a simple and intuitive way. Relying on similar motivations, we introduce the larger classes of 'loosely stratified' and 'constructively consistent' programs. Second, we give a formal basis for introducing quantifiers into queries and logic programs by defining 'constructively domain independent' formulas. Third, we extend the Generalized Magic Sets procedure to loosely stratified and constructively consistent programs, by relying on a 'conditional fixpoint' procedure.

Database applications often require to evaluate queries containing quantifiers or disjunctions, e.g., for handling general integrity constraints. Existing efficient methods for processing quantifiers depart from the relational model as they rely on non-algebraic procedures. Looking at quantified query evaluation from a new angle, we propose an approach to process quantifiers that makes use of relational algebra operators only. Our approach performs in two phases. The first phase normalizes the queries producing a canonical form. This form permits to improve the translation into relational algebra performed during the second phase. The improved translation relies on a new operator - the complement-join - that generalizes the set difference, on algebraic expressions of universal quantifiers that avoid the expensive division operator in many cases, and on a special processing of disjunctions by means of constrained outer-joins. Our method achieves an efficiency at least comparable with that of previous proposals, better in most cases. Furthermore, it is considerably simpler to implement as it completely relies on relational data structures and operators.