Giuseppe Pirrò

Semantic navigation on the web of data: specification of routes, web fragments and actions

The massive semantic data sources linked in the Web of Data give new meaning to old features like navigation; introduce new challenges like semantic specification of Web fragments; and make it possible to specify actions relying on semantic data. In this paper we introduce a declarative language to face these challenges. Based on navigational features, it is designed to specify fragments of the Web of Data and actions to be performed based on these data. We implement it in a centralized fashion, and show its power and performance. Finally, we explore the same ideas in a distributed setting, showing their feasibility, potentialities and challenges.

Completeness Statements about RDF Data Sources and Their Use for Query Answering

With thousands of RDF data sources available on the Web covering disparate and possibly overlapping knowledge domains, the problem of providing high-level descriptions (in the form of metadata) of their content becomes crucial. In this paper we introduce a theoretical framework for describing data sources in terms of their completeness. We show how existing data sources can be described with completeness statements expressed in RDF. We then focus on the problem of the completeness of query answering over plain and RDFS data sources augmented with completeness statements. Finally, we present an extension of the completeness framework for federated data sources.

Querying graphs with preferences

This paper presents GuLP a graph query language that enables to declaratively express preferences. Preferences enable to order the answers to a query and can be stated in terms of nodes/edge attributes and complex paths. We present the formal syntax and semantics of GuLP and a polynomial time algorithm for evaluating GuLP expressions. We describe an implementation of GuLP in the GuLP-it system, which is available for download. We evaluate the GuLP-it system on real-world and synthetic data.

The swget portal: Navigating and acting on the web of linked data

This paper presents the swget portal. By using the portal, users can instruct software modules to (virtually) move from one place (data source) to another on theWeb of Data, interpret knowledge and trigger actions much in the same spirit of intelligent agents. Instructions are specified via navigational expressions in the NautiLOD language. Such expressions are included into swget scripts that is, RDF documents that can be shared, modified, and reused. We discuss examples with real data in dierent scenarios showing the usefulness and potentialities of the portal. We also provide an evaluation of the performance of the portal.

The Logic of Extensional RDFS

The normative version of RDF Schema (RDFS) gives non-standard (intensional) interpretations to some standard notions such as classes and properties, thus departing from standard set-based semantics. In this paper we develop a standard set-based (extensional) semantics for the RDFS vocabulary while preserving the simplicity and computational complexity of deduction of the intensional version. This result can positively impact current implementations, as reasoning in RDFS can be implemented following common set-based intuitions and be compatible with OWL extensions.

Ontology: Definition Languages

Ontologies are artifacts used to model and represent in an explicit way knowledge related to a particular domain in terms of concepts, relations between concepts and axioms. In this article we provide an overview of ontology languages that have been defined under the umbrella of the W3C consortium. These language are characterized by different levels of expressiveness, starting from RDF, a simple language to express statements in the form of triples, to OWL, which enables very expressive forms of inference.

Ontology: Querying Languages and Development

Ontologies are a key support to provide a shared understanding of knowledge domains. Their flexibility and usefulness is witnessed in a variety of scenarios, from knowledge-based retrieval to projects like the Semantic Web. The possibility to express semantic information gave birth to a new class of query languages specifically designed. We will give an overview of one of such languages called SPARQL. SPARQL is the W3C standard to query data represented in RDF, another W3C standard. By using examples, we illustrate the structure of a SPARQL query. Then, we give an overview of popular ontology management tools.