80 research outputs found
The XML Query Language Xcerpt: Design Principles, Examples, and Semantics
Most query and transformation languages developed since the mid 90es for XML and semistructured dataāe.g. XQuery [1], the precursors of XQuery [2], and XSLT [3]ābuild upon a path-oriented node selection: A node in a data item is specified in terms of a root-to-node path in the manner of the file selection languages of operating systems. Constructs inspired from the regular expression constructs , +, ?, and āwildcardsā give rise to a flexible node retrieval from incompletely specified data items.
This paper further introduces into Xcerpt, a query and transformation language further developing an alternative approach to querying XML and semistructured data first introduced with the language UnQL [4]. A metaphor for this approach views queries as patterns, answers as data items matching the queries. Formally, an answer to a query is defined as a simulation [5] of an instance of the query in a data item
Initial Draft of a Possible Declarative Semantics for the Language
This article introduces a preliminary declarative semantics for a subset of the language Xcerpt (so-called
grouping-stratifiable programs) in form of a classical (Tarski style) model theory, adapted to the specific
requirements of Xcerptās constructs (e.g. the various aspects of incompleteness in query terms, grouping
constructs in rule heads, etc.). Most importantly, the model theory uses term simulation as a replacement
for term equality to handle incomplete term specifications, and an extended notion of substitutions in
order to properly convey the semantics of grouping constructs. Based upon this model theory, a fixpoint
semantics is also described, leading to a first notion of forward chaining evaluation of Xcerpt program
A contribution to the Semantics of Xcerpt, a Web Query and Transformation Language
Xcerpt [1] is a declarative and pattern-based query and transformation languag
Poster Presentation: Xcerpt and XChange ā Logic Programming Languages for Querying and Evolution on the Web
age Xcerpt and provides advanced, Web-specific capabilities, such as propagation of changes on the Web (change) and event-based communications between Web sites (exchange). Xcerpt: Querying Data on the Web Xcerpt is a declarative, rule-based query language for Web data (i.e. XML documents or semistructured databases) based on logic programming. An Xcerpt program contains at least one goal and some (maybe zero) rules. Rules and goals consist of query and construction patterns, called terms in analogy to other logic programming languages. Terms represent tree-like (or graph-like) structures. The children of a node may be either ordered (as in standard XML) or unordered (as is common in databases). Data terms are used to represent XML documents and the data items of a semistructured database. They are similar to ground functional programming expressions and logical atoms. A database is a (multi-)set of data terms (e.g. the Web). Query terms are patterns matched against Web resources
Development of Use Cases, Part I
For determining requirements and constructs appropriate for a Web query language, or in fact
any language, use cases are of essence. The W3C has published two sets of use cases for XML
and RDF query languages. In this article, solutions for these use cases are presented using
Xcerpt. a novel Web and Semantic Web query language that combines access to standard Web
data such as XML documents with access to Semantic Web metadata
such as RDF resource
descriptions with reasoning abilities and rules familiar from logicprogramming.
To the
best knowledge of the authors, this is the first in depth study of how to solve use cases for
accessing XML and RDF in a single language: Integrated access to data and metadata
has been
recognized by industry and academia as one of the key challenges in data processing for the
next decade. This article is a contribution towards addressing this challenge by demonstrating
along practical and recognized use cases the usefulness of reasoning abilities, rules, and
semistructured
query languages for accessing both data (XML) and metadata
(RDF)
Dependency Updates and Reasoning in KiWi
KiWi is a framework for semantic social software applica-
tions that combines the Wiki philosophy with Semantic Web technolo-
gies. Applications based on KiWi can therefore leverage i.a. reasoning
and versioning to follow both aspects and even go beyond existing tech-
nologies. For example, KiWi allows composition of content items, which
poses a challenge to the versioning system. In this paper we discuss ver-
sioning of composed content items and challenges related to reasoning in
collaborative social software, as both topics are concerned with updates
on the application state
Web and Semantic Web Query Languages
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
Identification of Design Principles
This report identifies those design principles for a (possibly new) query and transformation
language for the Web supporting inference that are considered essential. Based upon these
design principles an initial strawman is selected. Scenarios for querying the Semantic Web
illustrate the design principles and their reflection in the initial strawman, i.e., a first draft of
the query language to be designed and implemented by the REWERSE working group I4
Development of Use Cases, Part I
For determining requirements and constructs appropriate for a Web query language, or in fact
any language, use cases are of essence. The W3C has published two sets of use cases for XML
and RDF query languages. In this article, solutions for these use cases are presented using
Xcerpt. a novel Web and Semantic Web query language that combines access to standard Web
data such as XML documents with access to Semantic Web metadata
such as RDF resource
descriptions with reasoning abilities and rules familiar from logicprogramming.
To the
best knowledge of the authors, this is the first in depth study of how to solve use cases for
accessing XML and RDF in a single language: Integrated access to data and metadata
has been
recognized by industry and academia as one of the key challenges in data processing for the
next decade. This article is a contribution towards addressing this challenge by demonstrating
along practical and recognized use cases the usefulness of reasoning abilities, rules, and
semistructured
query languages for accessing both data (XML) and metadata
(RDF)
Survey over Existing Query and Transformation Languages
A widely acknowledged obstacle for realizing the vision of the Semantic Web is the inability
of many current Semantic Web approaches to cope with data available in such diverging
representation formalisms as XML, RDF, or Topic Maps. A common query language is the first
step to allow transparent access to data in any of these formats. To further the understanding
of the requirements and approaches proposed for query languages in the conventional as well
as the Semantic Web, this report surveys a large number of query languages for accessing
XML, RDF, or Topic Maps. This is the first systematic survey to consider query languages from
all these areas. From the detailed survey of these query languages, a common classification
scheme is derived that is useful for understanding and differentiating languages within and
among all three areas
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