María José Santofimia Romero - Grupo ARCO - Universidad de ...

concepts. Concept meanings cannot be considered in isolation, and there is a great amount of knowledgeinvolved in enhancing concepts with meaning. However, at some stage, it can be argued thatthe complexity involved in enhancing concepts with such a complex and large amount of knowledgecan make the task of context modeling unfeasible. It is therefore necessary to find an equilibriumbetween the amount of knowledge required to provide a close semantic description of a concept, andthe structure that allows such knowledge to be organized in a feasible way that can be used when reasoningand inferring about knowledge. Nevertheless, it should be remembered that ontology-basedapproaches have quickly achieved a high level of acceptance. The reason for this is mainly the factthat the knowledge modeled using an ontological approach can afterward be easily shared and reused.The first of the semantic models surveyed here also implements the same ontology-based approach.The AMIGO project [114] proposes an architecture specifically devoted to managing context information,built upon a semantic model of the context information, which at the same time is supportingthe information share among the different devices that populate the environment. The AMIGO semanticmodel understands context as being a physical context with different functional domains (i.e.PC, mobile, CE, and home automation). This project therefore proposes a complex structure of differentontologies, grouped in a modular manner [121]. The notion of action or event is ignored as itis the relationship of such concepts with the context devices.Additionally, the OWL-S, RDF, and SPARQL have been the technologies used for the implementationof the semantic model and for querying it. As was mentioned above both technologies havescaling problems associated to them, since whenever the ontology is getting more complex, queriesare taking exponentially increasing time in being evaluated. Moreover, SPARQL is basically a languagefor querying an ontology that does not support real inference mechanisms. In this sense, thereis not much difference between querying a database and an ontology. Nevertheless, despite the drawbacksassociated with the technologies employed, there are some strengths directly dependent on thesemantic modeling of services proposed by the AMIGO project.Regarding the service semantic modeling, the ontology-based service discovery and the dynamicservice composition are two of the most challenging goals addressed by the AMIGO project.The main contribution of the AMIGO semantic model is the tool they have developed to visuallyedit the context information ontology. The VantagePoint utility [70] facilitates the task of dealingwith the ontology context information for those that have not been trained in knowledge engineering.However, the semantic enhancement of services in AMIGO is basically intended to support semanticdiscovery and integration of Web services. However, the main drawback of this approach isgrounded in the fact that the use of semantics has to be associated to Web services. There exists a dependencyon the technology approach that needs to be implemented if services are to be semanticallydescribed.Aside from the technological aspects and focusing on the proposed model itself, the main shortageof the AMIGO semantic model is due to the service-centered approach it adopts. Despite beinglabeled as semantic, the accomplished service descriptions are not grounded in a knowledge base thatassociates meaning to the concepts, but rather, this approach is claimed to be semantic just on thebasis of the use of a common vocabulary. The role played by the proposed ontology is to standardizethe concepts involved in service descriptions, however, such ontology should be supported, at adifferent level, on the meaning and knowledge that each concept and relationship of the ontology hasassociated.However, ontology-based approaches are not the only strategies to context modeling, and thework in [139] and more recently the work in [11] present a survey of some the approaches employedfor modeling purposes.29