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CHAPTER 14 - Protection > 14.5 Implementation of Access Matrix

14.5 Implementation of Access Matrix

How can the access matrix be implemented effectively? In general, the matrix will be sparse; that is, most of the entries will be empty. Although data-structure techniques are available for representing sparse matrices, they are not particularly useful for this application, because of the way in which the protection facility is used. Here, we first describe several methods of implementing the access matrix and then compare the methods.

14.5.1 Global Table

The simplest implementation of the access matrix is a global table consisting of a set of ordered triples <domain, object, rights-set>. Whenever an operation M is executed on an object Oj within domain Di , the global table is searched for a triple < Di , Oj , Rk > , with MRk . If this triple is found, the operation is allowed to continue; otherwise, an exception (or error) condition is raised.

  

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