The main important aspect is physical data model is created after logical data model. For designing a logical data model one need not have through knowledge in any specific RDBMS like oracle, Informix and so on. This is because logical data model is created after having through study of the business entities which would be involved in the application. The same can be represented by using E-R diagram also called as Entity Relationship diagram which gives a diagrammatic representation of the study made on the business application.
The main aspect or quality a person must have to build a good logical data model is through understanding of the business, thorough knowledge about the application being modeled and very good understanding of relational theory for presenting the understanding in a structured manner. After the logical data model is built as specified above the physical data model comes into picture.
The logical data model built is used by business authors and analysts and after a through revision and review the physical data model is created. For creating a physical data model one must have good understanding of a specific RDBMS in which it would be built. This is because physical data model is represented using primary keys, foreign keys, triggers, referential integrity, constraints and so on that is specific for any RDMBS.