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Conceptual Graphs

With the emergence of high level services as found in the World Wide Web the need for an appropriate typing mechanism becomes evident. An application user (i.e. not a programmer) must deal with service types to lookup matching service providers. So far there exist only simple keyword based traders which allow only for a limited expressiveness of service types. We have chosen to develop a type specification based on conceptual graphs which are particularly useful to support the cognitive domain of the users.

Conceptual graphs have been developed to model the semantics of natural language. Service descriptions based on conceptual graphs are therefore intuitive in the sense that there is a close relationship to the way human beings represent and organize their knowledge. From an abstract point of view a conceptual graph is a finite, connected, directed, bipartite graph. The nodes of the graph are either concept or relation nodes. Due to the bipartite nature of the graphs, two concept nodes may only be connected via a relation node.

A concept node represents either a concrete or an abstract object in the world of discourse. As for the context of service types a concept may be a concrete object such as PRINTER, COMPILER or DATABASE including specific instances (e.g. HP-Laserjet, GCC, Ingres, etc), as well as an abstract object such as PRINTING-SPEED or PROGRAMMING-LANGUAGE with no physical representation. Whereas concepts model objects of our perception, a relation node expresses a specific relationship between concept nodes.

The following conceptual graph describes a vacation (concept nodes are surrounded by square brackets and relations by round brackets, respectively). The informal semantic of the concept is: A vacation in a city. During the vacation are cultural activities as concert and sightseeing offered. The duration of the vacation is 7 days.

Figure: Conceptual Graph describing the concept vacation

Within the AI-Trader Project we have developed a trader capable of processing service descriptions based on conceptual graphs. The implementation (including the complete sources) are freely available. A Java-ased frontend makes editing of conceptual graphs easy (the screenshot above came from this frontend). Some publications describe the philosophy behind the AI-Trader.