This paper proposes an algebraic semantics approach for data and object modeling. The approach captures the main concepts of object systems, namely : class, method, object identity, inheritance, overriding, overloading, late and early binding, collection types and persistence objects. The proposed model follows the algebraic aspects of relational database tradition; that is, the clear separation between schema, types (or domains), instance and query. For this reason it is enable to support an algebraic query language in the style of the relational algebra. Our approach also provides a rigorous mathematical treatment of null values in the object-oriented systems.