1. 1 CONCEPTUAL SCHEMA DESIGN PROCESS Information Processing and Technology, 2001 Yr 12 IPT

2. Last Lesson §Some entity types can be combined to save space in the CS Diagram. §Some entities can be derived from already existing entity types and their roles.

3. Design Cycle State Elementary Facts Entity types that should be combined and derivation. Add other constraints: value, cardinality, frequency and mandatory. 6. 4. Draw Conceptual Schema Diagram 1. 2. 3. 5.

4. Value Constraints §Value Constraints are a listing of allowed values for an entity type §They are used to limit instances for that object to members of a certain set. Student (name) Gender (letter) {M,F}

5. Cardinality Constraints §Cardinality constraints are similar to Value constraints but limit entities to a range of values. Student (name) Grade (letter) {A..E}

6. Frequency Constraints §Frequency Constraints define the number of times a particular role can be played. §Thus ample storage space can be allocated. Student (name) Subject (subject) <7

7. Mandatory Constraints §Mandatory role constraints indicate which roles must be played by all values of an entity type. §Roles without mandatory constraints are optional. These are easily identifiable from the population data (null values). §Mandatory roles are represented by the mandatory role dot.

8. Consider this data:

9. And its CS Diagram … Rock Star (name) Birth Year (year) Death Year (year) has 1. Does every Rock Star have a Birth Year? 2. Does every Birth Year have a Rock Star? 3. Does every Rock Star have a Death year? 4. Does every Death Year have a Rock Star? Yes No

10. Summary §Value and Cardinality constraints limit the value an entity type can have. §Frequency constraints limit the number of times a role can be played by its associated entities. §Roles are either mandatory or optional.