Assignments chapter 5
- Describe the purpose of a conceptual design.
It is used to describe the data contained in the database, the relationships between data items and the constraints on data.
- How is a conceptual design different from a logical design?
With logical design you don;t go into detail, with conceptual design you go into as much detail as possible.
- What is an external model?
Ahown as user sees them in real world.
- What is a conceptual model?
Present a logical structure of the database with the main data, but without detail. Also shows relationships among data.
- What is an internal model?
More like a phisical or file system and a representation of the database seen by the DBMS. Require the designer to match the conceptual model’s characteristics and constraints to those of the selected implementation model and involve mapping the entities in the conceptual model to the tables in the relational model.
- What is a physical model?
Are the physical representation of the database and managed by the OS.
- Which model does the database administrator work with?
Logical data model
- Which model does the end user work with?
External model
- What is logical data independence?
The ability to change the logical schema without changing the external schema.
- What is physical data independence?
The immunity of the internal model to changes in the physical mode.