## 4 Outline of the Approach
### Ontology for Ubiquitous User Modeling Interoperability  
In this section, we present a flexible ontology for ubiquitous user modeling interoperability (U2 MIO) and its relevance for the user-adaptive system proposed.  
The U2 MIO ontology:  
* Provides semantic support for user model overcoming differences between concepts at knowledge level.
* Represents a flexible user profile structure, with domain independency which provides the possibility for the ubiquitous user model to evolve during time.
* Provides representation for new profile suppliers and consumers that take part in the interoperability process without effort of the provider or consumer system.  
Figure 3: Architecture of adaptive system for profiles exchange and reuse.  
The ontology reuses SKOS ontology and it can be seen as an aggregation of concept schemes each one representing a profile supplier or consumer, and a central ubiquitous user model concept scheme. Semantic mapping relations are established between each supplier/consumer concept scheme and the ubiquitous user model concept scheme at concept level by the process of concept alignment in order to enable interoperability between user models.  
The ubiquitous user modeling ontology was set-up with Facebook, FOAF, and one profile of a specialized web application to monitor person's diet and physical activity of one user. This demands the design of four concept schemes, one for each profile provider and the ubiquitous user model concept scheme. Semantic mapping relations were established with SKOS properties. We used Prot@e ontology Editor for the set-up process.  
The ubiquitous user model concept scheme was set up with the basic skos:Collections shown in Figure 1 and their sub collections.  
We briefly described the adaptive system architecture for profile exchanges (Section 4.3). We describe the interrelations between profile supplier/consumer and the ubiquitous user modeling ontology (U2 MIO) in order to understand the relevance of the ontology and the process of concept alignment in the user modeling interoperability process (Figure 4).  
In a multi-application environment we can find many profile suppliers. Profile suppliers have user models (_um_) and their own transfer mechanisms (_tm_). The process of data extraction deals with providers' transfer mechanisms to collect the profile data from the sources and obtain source documents (_sd_) in XML, JSON or RDF. If a profile supplier is new to the system, a corresponding concept scheme (_C_) must be designed and added to the ubiquitous user modeling ontology by the model user mediator. The interoperability engine implements the process of concept alignment that: (i) determines the semantic mapping relations at concept level from the source concept scheme (_C_) to  
Figure 4: Interrelations between profile supplier/consumer and the ubiquitous user modeling ontology.  
the ubiquitous user model concept scheme (u2m); (ii) decides whether new concepts must be added to the ubiquitous user model concept scheme (u2m); (iii) decides whether new sub collections must be added to the ubiquitous user model concept scheme (u2m).  
If a new profile consumer wants reuse profile information, it is also necessary to build the corresponding concept scheme and semantic mapping from the request in case of Web services or a XML, JSON or RDF schema. The process of concept alignment to allow interoperability in heterogeneous sources is described in the next section. The innovation of this approach is that the central ubiquitous user model is not static and that the interoperability is enabled at concept level. The ontology can evolve over time.