Abstract: The ODMG Standard for object data management system consists of an Object Model for modeling applications, an Object Definition Language (ODL) for defining database schemas, and an Object Query Language (OQL) for writing queries. We present a formal system to specify the data types that can be defined in an ODL database schema and analyze the data types required by OQL queries. We indicate that OQL queries require data types beyond what can be defined in the ODL. With the current specification of the ODMG Standard, no compiler or interpreter could perform type checking for all the valid OQL queries.