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The proposed dynamic access control model is based on description logic (DL) augmented with a default (δ) and an exception ( ) operator to capture context features. Currently, this model has an expressivity almost comparable to OrBAC system (OrBAC (Organization Based Access Control) has been formalized in first order logic), all features needed for real attribution of authorization, i.e., assigning authorization to a user according to its role in an organization in a given context. A notable difference of our model is the allowing of composed context, the addition of new context and the deduction of new authorization depending on context.

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Recommendation systems can help internet users to find interesting things that match more with their profile. With the development of the digital age, recommendation systems have become indispensable in our lives. On the one hand, most of recommendation systems of the actual generation are based on Collaborative Filtering (CF) and their effectiveness is proved in several real applications. The main objective of this paper is to improve the recommendations provided by collaborative filtering using clustering. Nevertheless, taking into account the intrinsic relationship between users can enhance the recommendations performances. On the other hand, cooperative game theory techniques such as Shapley Value, take into consideration the intrinsic relationship among users when creating communities. With that in mind, we have used SV for the creation of user communities. Indeed, our proposed algorithm preforms into two steps, the first one consists to generate communities user based on Shapley Value, all taking into account the intrinsic properties between users. It applies in the second step a classical collaborative filtering process on each community to provide the Top-N recommendation. Experimental results show that the proposed approach significantly enhances the recommendation compared to the classical collaborative filtering and k-means based collaborative filtering. The cooperative game theory contributes to the improvement of the clustering based CF process because the quality of the users communities obtained is better.

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