Chapter 9

Methodology - Methodology -

Logical Database DesignLogical Database Design

Chapter 16 in Textbook

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ObjectivesObjectives

• 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

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Step 2Step 2 Build and Validate Build and Validate Local Logical Data ModelLocal 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

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Step 2.1 Step 2.1 Remove features not Remove features not compatible with the relational compatible with the relational

modelmodel

This involves:

– remove *:* recursive relationship types;

– remove complex relationship types;

– remove multi-valued attributes.

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Remove *:* Recursive Remove *:* Recursive Relationship TypesRelationship Types

STAFFsupervise

(0,*)

(0,*)

supervisor

supervisee

supervise STAFFSTAFF(0,*)(0,*)

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Remove Complex Relationship Remove Complex Relationship TypesTypes

register STAFFBRANCH

STAFFBRANCH

CLIENT

CLIENT

REGISTER

agree

processregister

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Step 2.2 Step 2.2 Derive relations for Derive relations for local logical data modellocal 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.

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Relations for the Staff View of Relations for the Staff View of DreamHomeDreamHome

Staff (staffNo, FName, Lname, position, sex, DOB, SupervisorStaffNo)Foreign Key SupervisorStaffNo reference Staff(StaffNo)

BusinessOwner (OwnerNo, BName, Btype, ContactName, address, TelNo)Alternate Key bNameAlternate Key TelNo

Lease (LeaseNo, PaymentMethod, depositPaid, RentStart, RentFinish, ClientNo, PropertyNo)Alternate Key PropertyNo, RentStartForeign Key ClientNo refrences Client(ClientNo)Foreign Key PropertyNo refrences Client(ClientNo)Derived deposit (PropertForRent.rent * 2)Derived duration (RentFinish -RentStart)

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Step 2Step 2 Build and Validate Build and Validate Local Logical Data ModelLocal 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.

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Step 2Step 2 Build and Validate Build and Validate Local Logical Data ModelLocal 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.

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Step 2Step 2 Build and Validate Build and Validate Local Logical Data ModelLocal 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.

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Referential Integrity Constraints Referential Integrity Constraints for Relationsfor 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 bNameAlternate Key TelNo

Lease (LeaseNo, PaymentMethod, depositPaid, RentStart, RentFinish, ClientNo, PropertyNo)Alternate Key PropertyNo, RentStartForeign Key ClientNo refrences Client(ClientNo) ON UPDATE CASCADE ON DELETE NO ACTIONForeign Key PropertyNo refrences Client(ClientNo) ON UPDATE CASCADE ON DELETE NO ACTIONDerived deposit (PropertForRent.rent * 2)Derived duration (RentFinish -RentStart)

Logical DB Design

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Step 2Step 2 Build and Validate Build and Validate Local Logical Data ModelLocal 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.

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Step 3Step 3 Build and validate Build and validate global logical data modelglobal 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

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Step 3.1 Merge local logical Step 3.1 Merge local logical data models into global modeldata 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.

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1. Review the names & contents of entities/relations and their CK

Branch View Entity Type CK

Branch BranchNo PostCodeTelephone TelNoStaff StaffNoManager StaffNoPrivateOwner OwnerNoBusinessOwner Bname telNoClient ClientNoPropertyForRent PropertynoLease LeaseNo PropertyNo RentStart ClientNo, RentStart

Staff View Entity Type CK

Staff StaffNo

PrivateOwner OwnerNoBusinessOwner Bname telNo OwnerNoClient ClientNoPropertyForRent PropertynoViewing ClientNo, PropertyNo

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2. Review the names & contents of relationships/FK

Branch View FK Relationship

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

Staff View FK Relationship

Relation

Branch

Telephone

Staff

Manager

PrivateOwner

BusinessOwner

Client

PropertyForRent

Viewing

supervisorStaffNo -> Staff(staffNo) Supervisor

StaffNo -> Staff(StaffNo) Registers

OwnerNo -> PrivateOwner(ownerNo) POwns

OwnerNo -> BOwns

BusinessOwner(ownerNo)

StaffNo -> Staff(StaffNo) Manages

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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)

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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.

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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.

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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.

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6. Include (without merging) relationships/FKs unique to each local model

Logical DB Design

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.

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Step 3Step 3 Build and Validate Build and Validate Global Logical Data ModelGlobal 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