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

tionally, the middleware architecture is arranged as a set of component frameworks in which eachcomponent is responsible for a specific functionality, such as service discovery, context, or resourcemanagement.The AURA project 16 [67] concerns about the discontinuity problem caused by the device dynamismthat characterizes a ubiquitous environment. The solution proposed by AURA is based onthe notion of a personal aura. This personal aura is nothing else but a component in charge of managingresource availability, providing service continuity and supporting users in their high-level tasks.The SOCAM architecture[55] is devoted to supporting the building and rapid prototyping ofcontext-aware and mobile services for intelligent cars. The cornerstone of the proposed architecturalapproach is an ontology-based context model. This context model supports a wide range of tasks,that are basically intended to reason about the context and to support interoperability among contextawaresystems. At the core of middleware architecture is the context interpreter module, in chargeof reasoning about context and holding the context knowledge. Additionally, there are some othermiddleware modules that are in charge of providing context abstractions or service discovery andlocation. Finally, the context-aware mobile services are responsible for using previous modules inorder to adapt the services to the current context.2.4 Semantic Models for Ambient IntelligenceSince a semantic model is the main contribution of this work, particular attention should be paid to thework concerning this topic which has been performed to date. Despite the recent efforts of the W3Cto provide a standardized and formal model of the environment, traditionally, there has existed a lackof consensus regarding the conceptual entities that should be part of the model. The Delivery ContextOntology [81] proposed by the W3C does not suffice to address the context-centered view advocatedin this work. On the contrary, it is characterized for adopting a device-centered approach, in whichthe focus is on capturing and modeling the context of use. Aside from the context of use, additionalissues should be considered in order to characterize and model the changes that make the contextevolve from one situation to a different one. These aspects, however, have not been considered in theDelivery Context Ontology.In this regard, the low level details with which the Delivery Context Ontology has describedthe environment concept are also responsible for its rigidity and the impossibility to adapt such anontology to different approaches, such as those focusing on users, user actions, or context events.This weakness has led to a situation in which each context-aware or Ambient Intelligence frameworkproposes their own specific model. The majority of the approaches tend to oversee the role playedby the modeling task, and the justification as to why a model is composed of certain concepts ratherthan others tends to be overlooked. Among the concepts that should be modeled in a semantic modelfor Ambient Intelligence, solely the notion of context has been properly formalized by the work in[1]. Furthermore, based on the definition provided by Dey and Abowd regarding the context notion,the work in [118] goes a step beyond how the context notion should be handled. Three differentlevels of context are considered, partially ordered by sets. Whatever the cause may be, apart from thecontext concept and the Ambient Intelligence or context-awareness field, no relevant work concerningconcepts such as actions and events has been found which can be cited here.Generally, the most common approach to context modeling is based on the use of a combinationof OWL with some query language, such as SPARQL. The first shortage that can be detectedin an ontology-based approach is due to the impossibility of attaching real meaning to the ontology16 http://www.cs.cmu.edu/~aura/28