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

Last Lesson §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.

Add other constraints: value, cardinality, frequency and mandatory. Design Cycle State Elementary Facts Entity types that should be combined and derivation Draw Conceptual Schema Diagram Add Uniqueness Constraints

Step 4. Add Uniqueness Constraints §Uniqueness constraints are specified in a conceptual schema to avoid data redundancy. §The relations are: l one to one l one to many l many to one l many to many

One to one §Does each friend have only one phone number? §Does each phone number have only one friend? Phone (number) Friend (name) has One friend has one phone number Yes

One to many §Does each party have only one minister? §Does each minister have only one party? Minister (name) Party (name) has One Party has many ministers Yes No

Many to one §Does each student have only one house? §Does each house have only one student? House (name) Student (name) has Many students have one house Yes No

Many to many §Does each teacher have only one subject? §Does each subject have only one teacher? Subject (name) Teacher (name) has Many teachers have many subjects. No

Ternary relationships (check this is always true) Subject (name) Student (name) stud ies Grade (letter) received

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

6. Perform Population and Final Checks. §The final Step of the CS Design Phase. §This step must check that the schema is: l internally consistent (no contradicting constraints) l externally consistent (population check) l free of redundancy (undetected derivations) l complete (fulfils original requirements and represents the UoD)

The End.