## 2 Ubiquitous User Modeling stakeholders  
There has been a great evolution of user modeling and adaptation from desktop paradigm to ubiquitous computing [11]. There are user models built in service provider's side described in [4] and models constructed by the user for personalization. In [3] it is stated that \"ubiquitous user modeling can be differentiated from generic user modeling by the three additional concepts: ongoing modeling, ongoing sharing and ongoing exploitation\". We are considering a ubiquitous user model that is application and system independent. Our user model must not only be independent of applications, devices and systems but must also allow the interoperability between distributed user profiles. It must allow ongoing sharing and reusing between heterogeneous sources in a changing environment. In recent years it has become clear that the user model representation must be able to evolve over time [8] due to the great deal of syntactical and structural differences between user models. It is practically impossible to develop a static commonly accepted ontology of the user modeling interoperability domain.A process of sharing and exchanging data of user profiles is necessary in order to achieve cooperation between systems and applications. Ubiquitous user modeling stakeholders play two main roles: profile information supplier, and profile information consumer. These roles can be played by different agents that can act in one or both roles simultaneously. Currently, a user has many profiles in different devices, applications and systems. Many personal gadgets have advanced sensors that gather data about the user on real time. We choose to work with social networks profiles, FOAF [12] and microformats, and personal devices with sensors. Social networking sites in particular, have become very successful and can be considered as valuable sources of personal information in order to build a user model. According to Nielsen, in a study published on March 2011 [13], people in the U.S. spent more time on Facebook than in any other website. Social network profiles can enrich user models from other providers too. These applications can be profile information suppliers and consumers at the same time. Semantic Web technologies such as FOAF and microformats represent an important step forward in terms of the Web's evolution. They provide a way to embed machine readable structured data into web pages for expressing user personal information [14]. We selected FOAF as an important profile supplier as it is currently considered as one of the best populated ontologies and is extensively adopted to describe users and their relations [15]. So, RDF documents published using FOAF vocabulary are valuable sources for our user model. Sensors attached to personal devices provide contextual information mainly about the user's. location, movement, distance and identity. Users' behaviour can also be collected through mobile devices such as smart phones that have built-in sensors [16]. Sensor devices deliver data relevant to healthcare, homeland security and tactical training that help to identify and handle situations on real-time [17]. In [18] the authors state that \"to progress towards a full harmonization between HMI systems and Sensor Web advances are needed in two fundamental areas: the integration and accessibility of a growing number of heterogeneous sensor data into HMI systems, and new mechanisms that allow sharing real-world information provided by users of connected objects into the Sensor Web or the Semantic Sensor Web\". In summary, profile information suppliers provide together valuable static, semi-static and dynamic information about the user. The major web sites are transformed into web services to really expose their content for reuse. Amazon is a pioneer in web services strategy for electronic commerce, and Yahoo has also began the transformation into structured information.