I present a technique for semantic query optimization (SQO) for object databases. The object schema and object query are translated into a DATALOG representation. Semantic knowledge about the object model and the particular application is expressed as integrity constraints. SQO is performed in the DATALOG representation and an equivalent logic query, and subsequently an equivalent object query, is obtained. SQO is based on the residue technique of Chakravarthy, Grant and Minker (1990). This technique generalizes previous research on SQO for object databases. It can also be applied to queries with methods and structure constructors and to utilize access support relations.