21. A database query system according to claim 19 wherein said query generator converts said intermediate language query into said target language by a set of successive transformations.
21. A database query system according to claim 19 wherein said query generator converts said intermediate language query into said target language by a set of successive transformations. 23. A database query system according to claim 21 wherein said set of transformations comprises: a set of structural transformations; a set of transformation to include inferred information; and a set of transformations by pattern substitution.