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Abstract:
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Semi-structured, hierarchical representation using XML are now widely used for information storage and exchange of complex data such as medical records. Hierarchical representation allows administrators to express access control to different components of the data based on the role of the user in the organization and significance of components. A great advantage of using XML schema is that different instances of data of varying complexity can be accommodated. Hierarchical structures also allow fine-grained access control, because access control can be defined for any node of the hierarchy. Thus, databases of XML documents offer significant advantages over traditional relational databases. Moreover, semantics of XML documents for access control are quite different. In general, the access control is given in form of rules which describe whether to grant or deny access to a node, only to descendants of the node, or all. In order to apply these rules to user queries, it is advantageous to translate them and store in form a table, called Access-Condition Table (ACT). It is also necessary to propagate access rules to descendant nodes and apply additional semantics, if any. ACT does these at a pre-processing phase to eliminate their costs leaving just Boolean conditions to be checked at runtime. The purpose of this thesis is to study an implementation of an automatic generation of ACT, which can be used by the query evaluator to test if the permission is granted before starting time consuming database retrieval operations. Use of ACT saves time consuming access rules at run-time. |