A method and mechanism are provided for accessing data. Values are stored for a set of context attributes associated with a session between a database user and a database server. The database system includes an attribute setting mechanism that selectively restricts access to the set of context attributes based on a policy. During the session, the database server executes a query that contains a reference to one or more of the context attributes. For example, the query may contain a predicate that requires a comparison between a context attribute value and a constant. The database server processes the query based on current values of the one or more of the context attributes referenced in the query. A mechanism is also provided for dynamically attaching predicates to queries, where the predicates are attached based on a policy. For example, the database system detects that a query is issued against a database object. Prior to executing the query, a policy function associated with the database object is invoked. The policy function creates a modified query by selectively adding zero or more predicates to the query based on a policy associated with the database object. The modified query is then executed.