In a decentralised knowledge representation system such as the W eb of Data, it is common and indeed desirable for different knowledge graphs to overlap. Whenever multiple names are used to denote the same thing, owl:sameAs statements are needed in order to link the data and foster reuse. Whilst the deductive value of such identity statements can be extremely useful in enhancing various knowledge-based systems, incorrect use of identity can have wide-ranging effects in a global knowledge space like the W eb of Data. With several works already proven that identity in the W eb is broken, this survey investigates the current state of this "sameAs problem". An open discussion highlights the main weaknesses suffered by solutions in the literature, and draws open challenges to be faced in the future.

This paper presents an empirical study aiming at understanding the modeling style and the overall semantic structure of Linked Open Data. We observe how classes, properties and individuals are used in practice. We also investigate how hierarchies of concepts are structured, and how much they are linked. In addition to discussing the results, this paper contributes (i) a conceptual framework, including a set of metrics, which generalises over the observable constructs; (ii) an open source implementation that facilitates its application to other Linked Data knowledge graphs.

Articulating thought in computer-based media is a powerful means for humans to develop their understanding of phenomena. We have created DynaLearn, an Intelligent Learning Environment that allows learners to acquire conceptual knowledge by constructing and simulating qualitative models of how systems behave. DynaLearn uses diagrammatic representations for learners to express their ideas. This article presents an overview of the DynaLearn system.

Articulating thought in computer-based media is a powerful means for humans to develop their understanding of phenomena. We have created DynaLearn, an Intelligent Learning Environment that allows learners to acquire conceptual knowledge by constructing and simulating qualitative models of how systems behave. DynaLearn uses diagrammatic representations for learners to express their ideas. The environment is equipped with semantic technology components capable of generating knowledge-based feedback, and virtual characters enhancing the interaction with learners. Teachers have created course material, and successful evaluation studies have been performed. This article presents an overview of the DynaLearn system.

The success of the Web of Data (WOD) is based on the thorough understanding of, and agreement upon, the se- mantics of data and ontologies. But the Web of Data as a whole is complex, and inherently messy, contex- tualised, opinionated, in short: it is a market-place of ideas, rather than a database. Existing paradigms are in- appropriate for dealing with this new type of knowledge structures. The urgency of dealing with the non-standard charac- teristics of the Web of Data has been recognised, and separate initiatives try to tackle its individual manifes- tations, e.g. inconsistencies, contexts, vagueness, prove- nance, etc. Tomorrow’s Web of Data requires novel se- mantics with efficient (generic) implementations to en- sure semantic clarity, reuse and interoperability. We recently introduced pragmatic semantics as a new semantic paradigm integrating elements from market theory and classical semantics into a framework of op- timisation over truth-orderings, each representing a par- ticular world-view. We propose nature-based algorithms to implement those semantics. We recently started a new research project, called PraSem, with the goal of investigating Pragmatic Semantics both from a theoret- ical and practical perspective.

Identity relations are at the foundation of the Linked Open Data initiative and on the Semantic Web in gen- eral. They allow the interlinking of alternative descrip- tions of the same thing. However, many practical uses of owl:sameAs are known to violate its formal seman- tics. We propose a method that assigns meaning to (the subrelations of) an identity relation using the predicates of the dataset schema. Applications of this approach include automated suggestions for asserting/retracting identity pairs and quality assessment. We also describe an experimental design for this approach.