1. Logical Database Design
Chapter 9
Methodology -
Logical Database Design
Chapter 16 in Textbook

2. Objectives
Remove features from a local conceptual model that are not compatible with the relational model.
Map the conceptual model into relations.
Validate these relations using the technique of normalization.
Validate a logical data model to ensure it supports required user transactions.
Merge local logical data models based on specific views into a global logical data model of the enterprise.
Ensure that resultant global model is a true and accurate representation of enterprise.
Logical DB Design

3. Step 2 Build and Validate Local Logical Data Model
Step 2.1 Remove features not compatible with the relational model
Step 2.2 Derive relations for local logical data model
Step 2.3 Validate relations using normalization
Step 2.4 Validate relations against user transactions
Step 2.5 Define integrity constraints
Step 2.6 Review local logical data model with user
Logical DB Design

4. Step 2.1 Remove features not compatible with the relational model
This involves:
remove *:* recursive relationship types;
remove complex relationship types;
remove multi-valued attributes.
Logical DB Design

5. Remove *:* Recursive Relationship Types
supervisor
supervise
(0,*)
STAFF
supervisee
(0,*)
STAFF
STAFF
supervise
(0,*)
(0,*)
Logical DB Design

6. Remove Complex Relationship Types
BRANCH
STAFF
register
CLIENT
BRANCH
register
REGISTER
process
STAFF
agree
CLIENT
Logical DB Design

7. Step 2.2 Derive relations for local logical data model
Objective: To create relations for the local logical data model to represent the entities, relationships, and attributes that have been identified.
Strong entity types.
Weak entity types.
1:1 binary relationship types.
1:M relationship types.
1:1 recursive relationship types.
Superclass/Subclass relationship types.
M:N relationship types.
Document relations and foreign key attributes.
Logical DB Design

8. Relations for the Staff View of DreamHome
Staff (staffNo, FName, Lname, position, sex, DOB, SupervisorStaffNo)
Foreign Key SupervisorStaffNo
reference Staff(StaffNo)
BusinessOwner (OwnerNo, BName, Btype, ContactName, address, TelNo)
Alternate Key bName
Alternate Key TelNo
Lease (LeaseNo, PaymentMethod, depositPaid, RentStart, RentFinish, ClientNo, PropertyNo)
Alternate Key PropertyNo, RentStart
Foreign Key ClientNo refrences Client(ClientNo)
Foreign Key PropertyNo refrences Client(ClientNo)
Derived deposit (PropertForRent.rent * 2)
Derived duration (RentFinish -RentStart)
Logical DB Design

9. Step 2 Build and Validate Local Logical Data Model
Step 2.3 Validate relations using normalization
Objective: To ensure that each relation is in at least BCNF.
Step 2.4 Validate relations against user transactions
Objective: To ensure that the relations in the local logical data model support the transactions required by the view.
Logical DB Design

10. Step 2 Build and Validate Local Logical Data Model
Step 2.5 Define integrity constraints
Integrity constraints protects DB from being inconsistent.
Types of integrity constraints:
Required data.
Entity integrity.
Referential integrity.
Attribute domain.
Enterprise constraints.
Logical DB Design

11. Step 2 Build and Validate Local Logical Data Model
In testing referential integrity check the following cases:
Insert tuple into child relation.
Delete tuple from child relation.
Update FK of child tuple.
Insert tuple into parent relation.
Delete tuple from parent relation.
Update PK of parent tuple.
Logical DB Design

12. Referential Integrity Constraints for Relations
Staff (staffNo, FName, Lname, position, sex, DOB, SupervisorStaffNo)
Foreign Key SupervisorStaffNo reference Staff(StaffNo)
ON UPDATE CASCADE ON DELETE SET NULL
BusinessOwner (OwnerNo, BName, Btype, ContactName, address, TelNo)
Alternate Key bName
Alternate Key TelNo
Lease (LeaseNo, PaymentMethod, depositPaid, RentStart, RentFinish, ClientNo, PropertyNo)
Alternate Key PropertyNo, RentStart
Foreign Key ClientNo refrences Client(ClientNo)
ON UPDATE CASCADE ON DELETE NO ACTION
Foreign Key PropertyNo refrences Client(ClientNo)
Derived deposit (PropertForRent.rent * 2)
Derived duration (RentFinish -RentStart)
Logical DB Design

13. Step 2 Build and Validate Local Logical Data Model
Step 2.6 Review local logical data model with user
Objective: To ensure that the local logical data model and supporting documentation that describes the model is a true representation of the view.
Logical DB Design

14. Step 3 Build and validate global logical data model
Combine the individual local logical data models into a single global logical data model that represents the enterprise.
Step 3.1 Merge local logical data models into global model
Step 3.2 Validate global logical data model
Step 3.3 Check for future growth
Step 3.4 Review global logical data model with users
Logical DB Design

15. Step 3.1 Merge local logical data models into global model
1. Review the names & contents of entities/relations and their CK.
2. Review the names & contents of relationships/FK.
3. Merge entities/relations from the local models.
4. Include (without merging) entities/relations unique to each local model.
5. Merge relationships/FK from the local models.
6. Include (without merging) relationships/FKs unique to each local model.
7. Check the missing entities/relations and relationships/FKs.
8. Check FKs.
9. Check integrity constraints.
10. Draw the global ER/relation diagram.
11. Update the documentation.

16. 1. Review the names & contents of entities/relations and their CK
Branch View
Entity Type CK
Staff View
Entity Type CK
Branch BranchNo
PostCode
Telephone TelNo
Staff StaffNo
Manager StaffNo
PrivateOwner OwnerNo
BusinessOwner Bname
telNo
Client ClientNo
PropertyForRent Propertyno
Lease LeaseNo
PropertyNo
RentStart
ClientNo, RentStart
Staff StaffNo
PrivateOwner OwnerNo
BusinessOwner Bname
telNo
OwnerNo
Client ClientNo
PropertyForRent Propertyno
Viewing ClientNo, PropertyNo
Logical DB Design

17. 2. Review the names & contents of relationships/FK
Branch View
FK Relationship
Staff View
FK Relationship
Branch
Telephone
Staff
Manager
PrivateOwner
BusinessOwner
Client
PropertyForRent
Viewing
mgrStaffNo -> Manager(StaffNo) Manages
branchN -> Branch(branchNo)
supervisorStaffNo -> Staff(staffNo) Supervisor
branchNo -> Branch(branchNo)
StaffNo -> Staff(StaffNo)
OwnerNo -> PrivateOwner(ownerNo) Owns
OwnerNo -> Owns
BusinessOwner(ownerNo)
StaffNo -> Staff(StaffNo) Oversees
BranchNo -> Branch(BranchNo) Offers
supervisorStaffNo -> Staff(staffNo) Supervisor
StaffNo -> Staff(StaffNo) Registers
OwnerNo -> PrivateOwner(ownerNo) POwns
OwnerNo -> BOwns
BusinessOwner(ownerNo)
StaffNo -> Staff(StaffNo) Manages
Logical DB Design

18. 3. Merge entities/relations from the local models
1. Merge entities/relations with the same name & the same PK.
Branch View Staff View
PRIVATE OWNER(Ono, name, address) PRIVATE OWNER(Ono, fname, lname, address)
Global View
PRIVATE OWNER(Ono, fname, lname, address)
Logical DB Design

19. 3. Merge entities/relations from the local models
2. Merge entities/relations with the same name but different PK.
Branch View Staff View
BOWNER(bName, bType, address) BOWNER(Ono, bName, bType, address)
AK telNo AK bName, telNo
Global View
BOWNER(Ono, bName, bType, address)
AK bName, telNo
3. Merge entities/relations with the different names using the same or different PK.
Logical DB Design

20. 4. Include (without merging) entities/relations unique to each local model
The Previous task should identify all entities/relations that are the same.
All remaining entities/relations are included in the global model without change.
Logical DB Design

21. 5. Merge relationship/FK from the local models
1. Merge relationship/FKs with the same name & the same purpose.
2. Merge relationship/FKs with different names but the same purpose.
Logical DB Design

22. 6. Include (without merging) relationships/FKs unique to each local model
Again, the Previous task should identify all relationships/FKs that are the same.
All remaining relationships/FKs are included in the global model without change.
Logical DB Design

23. Step 3 Build and Validate Global Logical Data Model
Step 3.2 Validate global logical data model
Objective: To validate the relations created from the global logical data model using the technique of normalization and to ensure they support the required transactions, if necessary.
Step 3.3 Check for future growth
Objective: To determine whether there are any significant changes likely in the foreseeable future and to assess whether the global logical data model can accommodate these changes.
Step 3.4 Review global logical data model with users
Objective: To ensure that the global logical data model is a true representation of the enterprise.
Logical DB Design