9. A computer program product comprising a computer useable memory device having a computer readable program stored thereon, wherein the computer readable program when executed on a computer causes the computer to: provide a pre-defined logical schema to a user of a database system, wherein the pre-defined logical schema is mapped to at least two relational database entities of different databases storing data therein; receive a logical query for data stored in the databases from the user, wherein the logical query is written in an object-oriented query language utilizing the pre-defined logical schema, and comprises two or more predicates and an operator specifying an action to take with one or more of the predicates; in response to receiving the logical query, interpret the logical query using the pre-defined logical schema to determine which of the relational database entities is a subject of the logical query, and which of the relational database entities is associated with each predicate; request the database of each determined relational database entity of the logical query to: translate each of the associated predicates of that database in the logical query into a query language specific to that database, wherein at least two different databases translate an associated predicate; and apply an authorization rule with each of the associated predicates of that database in the logical query, wherein the authorization rule identifies unauthorized data; receive a translated predicate query for each determined predicate of the logical query from its associated database of the relational database entity, wherein each translated predicate query is written in a relational query language specific to the associated database and is a translation of one of the object-oriented predicates in the logical query; combine each translated predicate query received from the databases of the determined relational database entities into a master query using the operator; execute the master query against the databases of the relational database entities that are subjects of the logical query; in response to executing the master query, receive a query result set from the databases of the relational database entities that are subjects of the logical query; and provide the query result set to the user, wherein the query result set lacks the unauthorized data.
9. A computer program product comprising a computer useable memory device having a computer readable program stored thereon, wherein the computer readable program when executed on a computer causes the computer to: provide a pre-defined logical schema to a user of a database system, wherein the pre-defined logical schema is mapped to at least two relational database entities of different databases storing data therein; receive a logical query for data stored in the databases from the user, wherein the logical query is written in an object-oriented query language utilizing the pre-defined logical schema, and comprises two or more predicates and an operator specifying an action to take with one or more of the predicates; in response to receiving the logical query, interpret the logical query using the pre-defined logical schema to determine which of the relational database entities is a subject of the logical query, and which of the relational database entities is associated with each predicate; request the database of each determined relational database entity of the logical query to: translate each of the associated predicates of that database in the logical query into a query language specific to that database, wherein at least two different databases translate an associated predicate; and apply an authorization rule with each of the associated predicates of that database in the logical query, wherein the authorization rule identifies unauthorized data; receive a translated predicate query for each determined predicate of the logical query from its associated database of the relational database entity, wherein each translated predicate query is written in a relational query language specific to the associated database and is a translation of one of the object-oriented predicates in the logical query; combine each translated predicate query received from the databases of the determined relational database entities into a master query using the operator; execute the master query against the databases of the relational database entities that are subjects of the logical query; in response to executing the master query, receive a query result set from the databases of the relational database entities that are subjects of the logical query; and provide the query result set to the user, wherein the query result set lacks the unauthorized data. 10. The computer program product of claim 9 , wherein the computer readable program when executed on a computer further causes the computer to: request the database of each relational database entity to check for authorization for each of its associated predicates; receive the authorization rule for each predicate from its associated database of the relational database entity, wherein the authorization rule specifies unauthorized data and is written in the relational query language; wherein said combining further comprises combining the authorization rules with the translated predicate queries into the master query such that the received query result set does not contain any unauthorized.