Abstract:In this paper, our objeetive is to define a seeurity model for regulating aeeess to XML documents. Our model offers a seeurity poliey with a great expressive power. An XML document is represented by a tree. Nodes of this tree are of different type (element, attribute, text, comment...etc). The smaIlest protection granularity of our model is the node, that is, authorisation rules granting or denying access to a single node can be defined. The authorisation mIes related to a specific XML document are first defined on aseparate Authorisation sheet. This Authorisation sheet is then translated into an XSLT sheet. If a user requests access to the XML doeument then the XSLT processor uses the XSLT sheet to provide the user with a view of the XML document which is eompatible with his rights.

While the RGB color model refers to the biological processing of colors in the human visual system, the HSV color model corresponds to the human perception of color similarity. In this paper we formulate a projection of RGB vectors within the RGB color space, which separates achromatic from chromatic information. The projection is the mathematical equivalent to Hue and Saturation of the HSV color space in the RGB space. It integrates the psycho-visual concept of human differentiation between colors of the HSV space into the physiological-visual based concept of the RGB space. With the projection it is, contrary to the prevailing opinion, possible to differentiate between colors based on human perception in the linear geometry of the RGB color space. This opens new possibilities in many fields of color image processing, especially in the domain of color image segmentation, where color similarity plays a major role.

Existing security models for RDF use RDF patterns for defining the security policy. This approach leads to a number of security rules which rapidly tends to be unmanageable. In this paper we define a new security model which follows the traditional approach of creating security views, which has long been used by SQL database administrators. Our model first logically distributes RDF data into SPARQL views and then it defines security rules regulating SPARQL access to views. Moreover our model supports rights delegation and dynamic security rules (i.e. rules which can be active or not, depending on the context).

In this paper, we define a security model for a native XML database which supports the Xupdate language. Our model is inspired by the SQL security model which is the most famous security model for database. We first define a generic access control model for tree data structures. Then, we apply our model to an XML database which supports the Xupdate language.

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Access control models for XML data can be classified in two major categories: node filtering and query rewriting systems. The first category includes approaches that use access policies to compute secure user views on XML data sets. User queries are then evaluated on those views. In the second category of approaches, authorization rules are used to transform user queries to be evaluated against the original XML dataset. The aim of this paper is to describe a model combining the advantages of these approaches and overcoming their limitations. The model specification is given using a Finite State Automata, ensuring generality and easiness of standardization w.r.t. specific implementation techniques

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