In the initial stages of database design, database designers develop a conceptual schema as a basis for users to express their data needs. The conceptual schema can be modified after receiving user feedback. This chapter shows how the conceptual schema presented in semantic objects can be easily converted into the logical schema presented in the relational data model, which is the most common logical data model. A data model is a set of concepts that can be used to describe the whole structure of a database, which is called the schema. In the process of database design, a schema is represented in three levels of data models: conceptual, logical, and physical data models. The primary conceptual data model has been the entity-relationship model. Users should be given opportunities to express their needs of data in the so-called miniworld, which is the part of the real world to be represented in the schema.