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Alternative Semantics. Pragmatic Semantics. Deep Semantics.

altsemantics is about alternative semantics for the Web of Data.

The Web of Data has become an enormous dynamic network of typed links between data sets stored on different computers all over the world. These data sets are machine readable and unambiguously interpretable, thanks to their underlying standard representation languages, such as RDF or OWL. The expressiveness and flexibility of the publication model of Linked Data has led to its widespread adoption and an ever increasing publication of semantically rich data on the Web.

This success however has started to create serious problems as the scale and complexity of information outgrows the current methods in use, which are mostly based on database technology and expressive knowledge representation formalism such as Modal and Description Logics. While  the logical underpinning of both formalisms was key to its initial success due to its formal rigor and formal simplicity, it is becoming more and more apparent that the complexity of the world, with its contextualised views are often insufficiently understood when data is interpreted in the traditional model-theoretic view alone. In our view, alternative semantics for traditional logical languages have to be studied and exploited to allow for richer use of the immense source of knowledge the Web of Data has become.

Metro meaning

While traveling the Amsterdam metro the other day a person standing behind me told another person that you could identity a city’s center by looking at its subway network. The center is oftentimes inside an oval with lines leaving the oval.

Even though this statement is not true for the general case, it contains the valid thought or suggestion that structure is at least correlated with and maybe indicative of meaning. There is a sense in which structure, a river for commerce, roads for transportation, has made it possible for a city to be formed at a certain spot (structure predating the city). Then, once the city grows, structure is added and/or changed, e.g. by adding subways.

In some sense knowledge of the structure of transportation and communication channels induces knowledge of where cities are. If we would have to explain to an outer-worldly visitor what a ‘city’ is, both showing a transportation map and giving a historic account of the original transportation route (e.g., the main river around which a city was formed) seem apropriate ways to start.

The metro map of Paris.

What are Pragmatic Semantics?

What is the problem?

The Web of Data (WOD) connects data in a similar way as the WWW connects documents. Atomic data-units called resources are connected via typed links with arbitrary resources anywhere on the Web, and together these RDF triples form a gigantic graph of linked data. The meaning of the types can be fixed using standardised schema and ontology languages such as RDFS and OWL. The semantics of these languages are based on logical paradigms that were designed for small and hand-made knowledge bases, and come with a classical model-theory assigning truth to formulae, and entailment based on this truth. In a highly complex, dynamic, context-dependent, opinionated, contradictory and multi-dimensional semantic network as the WOD, these Semantics are insufficient, as they are one-dimensional, often prone to logical fallacies, and usually intractable.

On the Web in general, and the Web of Data in particular, almost every bit of information is context-dependent, biased towards a particular viewpoint, opinionated, dated, uncertain or vague. The WOD is a market-place of ideas, not a database, and has to be dealt with accordingly. As making the representational languages more complex is not an option, we have to adapt the formal semantics of existing formalisms to the new requirements.

Pragmatic Semantics

Pragmatic semantics integrate different world-views instead of defining meaning with respect to a single one. The idea is to make as much information in the data explicit, and turn it into first-class semantics citizens. First, it allows integrating classic model-theoretic notions of truth with explicit knowledge about the structure of the knowledge base. But also semantic meta-data, such as popularity, scarcity, abnormality, etc., and even background knowledge from other sources, can be integrated.

Interoperability is then achieved by enriching an ontology with meta-information about semantic orderings, as well as agreement on the weighting of orderings. As there are possibly several pragmatic closures (different solutions on the Pareto-front) also agreement on the weighting of features is required. We will refer to the entailment induced by a given set of orderings as an instantiation of the family of pragmatic semantics.

PhD position

The Knowledge Representation and Reasoning Group at the Vrije Universiteit Amsterdam is looking for an enthusiastic PhD student to work on the NWO funded PraSem Project on Pragmatic Semantics for the Web of Data. Interested students with a Master in Computer Science, Artificial Intelligence, Logic or related topics should send their application no later than 15 June 2012 to schlobac@few.vu.nl.

More information about Pragmatic Semantics can be found in the original project proposal.

More information about how to apply can be found here: Open PhD position

If you want more information, please do not hestitate contacting me: schlobac@few.vu.nl