1. Chapter 8 Methodology - Conceptual Database Design Chapter 15 in Textbook

2. 2 Design Methodology A structured approach that uses procedures, techniques, tools, and documentation aids to support and facilitate the process of design. Conceptual DB Design

3. 3 Database Design Physical DB design Logical DB design Conceptual DB design Hardware dependent Software dependent Hardware independent Software dependent Hardware independent Software independent Conceptual DB Design

4. 4 Success Factors in Database Design Work interactively with users as much as possible. Follow a structured methodology throughout the data modelling process. Employ a data-driven approach. Incorporate structural and integrity considerations into the data models. Combine conceptualization, normalization, and transaction validation techniques into the data modelling methodology. Use diagrams to represent as much of the data models as possible. Build a data dictionary to supplement the data model diagrams. Be willing to repeat steps. Conceptual DB Design

5. 5 Design Methodology Overview Step 1 Build local conceptual data model for each user view. Step 2 Build and validate local logical data model for each view. Step 3 Build and validate global logical data model. Step 4 Translate global logical data model for target DBMS. Step 5 Design physical representation. Step 6 Design user views. Step 7 Design security mechanisms. Step 8 Consider the introduction of controlled redundancy. Step 9 Monitor and tune the operational system. Conceptual DB Design

6. 6 Methodology Overview – Conceptual Database Design Step 1 Build local conceptual data model for each user view Step 1.1 Identify entity types. Step 1.2 Identify relationship types. Step 1.3 Identify and associate attributes with entity or relationship types. Step 1.4 Determine attribute domains. Step 1.5 Determine candidate and primary key attributes. Step 1.6 Consider use of enhanced modeling concepts (optional step). Step 1.7 Check model for redundancy. Step 1.8 Validate local conceptual model against user transactions. Step 1.9 Review local conceptual data model with user.

7. 7 Methodology Overview – Logical Database Design for Relational Model Step 2 Build and validate local logical data model for each view Step 2.1 Derive relations for local logical data model. Step 2.2 Validate relations using normalization. Step 2.3 Validate relations against user transactions. Step 2.4 Define integrity constraints. Step 2.5 Review local logical data model with user. Conceptual DB Design

8. 8 Methodology Overview – Logical Database Design for Relational Model Step 3 Build and validate global logical data model 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. Conceptual DB Design

9. 9 Methodology Overview – Physical Database Design for Relational Model Step 4 Translate global logical data model for target DBMS Step 4.1 Design base relations. Step 4.2 Design representation of derived data. Step 4.3 Design enterprise constraints. Step 5 Design physical representation Step 5.1 Analyze transactions. Step 5.2 Choose file organization. Step 5.3 Choose indexes. Step 5.4 Estimate disk space requirements.

10. 10 Methodology Overview – Physical Database Design for Relational Model Step 6 Design user views Step 7 Design security mechanisms Step 8 Consider the introduction of controlled redundancy Step 9 Monitor and tune the operational system Conceptual DB Design

11. 11 Step 1 Build Local Conceptual Data Model for Each View Objective: To build a local conceptual data model of an enterprise for each specific view. Step 1.1 Identify entity types Objective: To identify the main entity types that are required by the view; Document entity types in data dictionary. Conceptual DB Design

12. 12 Data Dictionary for Staff View Showing Description of Entities Entity Name Description Aliases Occurrence Staff General term describing all staff Employee Each member of staff works at one employed by DearmHome particular branch PropertyForRent General term describing all Property Each property has a single owner & property for rent is available at one specific branch, where the property is managed by 1 member of staff. A property is viewed by many clients and rented by a single client at a time Conceptual DB Design

13. 13 Step 1 Build Local Conceptual Data Model for Each View Step 1.2 Identify relationship types Objective: To identify the important relationships that exist between the entity types that have been identified. – Check for binary, complex, recursive relationship types. – Check for explicit, and implicit relationship types. – Use ER diagrams. – Determine multiplicity of relationships. – Check for fan and chasm traps. – Check that each entity participate in at least one relationship. – Document relationship type. Conceptual DB Design

14. ERD for Staff View of DreamHome BUSINESS OWNER STAFF PROPERTY PRIVATE OWNER LEASE CLIENT PREFERENCE POwn holdassociate manage state superviseregister BOwn (1:1) (0,*) (0,1) (1,*) (0,1) (0,100) views (0,*) supervisor supervisee

15. 15 Data Dictionary for Staff View Showing Description of Relationships Entity Name Multiplicity Relationship Entity Name Multiplicity Staff 0..1 Manages PropertyForRent 0..100 0..1 Supervises Staff 0..10 PropertyForRent 1..1 AssociatedWith Lease 0..* Conceptual DB Design

16. 16 Step 1 Build Local Conceptual Data Model for Each View Step 1.3 Identify and associate attributes with entity or relationship types Objective: To identify and associate attributes with the appropriate entity or relationship types and document the details of each attribute. For entity list what information are we required to hold on? –Check simple & composite attributes. –Check single & multi-valued attributes. –Derived attributes. –Check for shared attributes. –Document the attribute. Conceptual DB Design

17. 17 Step 1 Build Local Conceptual Data Model for Each View Step 1.4 Determine attribute domains Objective: To determine domains for the attributes in the local conceptual model and document the details of each domain. –Data type. –Size. –Allowable value. –Default value. Conceptual DB Design

18. 18 Data Dictionary for Staff View Showing Description of Attributes Entity Attribute Description Data Length Nulls Multi- Default Range PK Name Type Valued Value Staff StaffNo Uniquely identifies a staff member varchar 5 No No Y name FName First name of Staff varchar 15 No No Lname Last name of Staff varchar 15 No No position Job title of member of staff varchar 10 No No sex Gender of member of staff character 1 Yes No M F, M DOB Date of Birth of member of staff Date Yes No 1960-1990 Conceptual DB Design

19. 19 Step 1 Build Local Conceptual Data Model for Each View Step 1.5 Determine candidate and primary key attributes Objective: To identify the candidate key(s) for each entity and if there is more than one candidate key, to choose one to be the primary key. CK must be: –minimal set of attributes. –least likely to have its value changed. –fewest size or smallest maximum number. –easiest to use from the user’s point of view. Step 1.6 Consider use of enhanced modeling concepts Objective: To consider the use of enhanced modeling concepts, such as specialization / generalization, aggregation, and composition. Conceptual DB Design

20. ERD with PK BUSINESS OWNER STAFF PROPERTY PRIVATE OWNER LEASE CLIENT PREFERENCE POwn holdassociate manage state superviseregister BOwn (1:1) (0,*) (0,1) (1,*) (0,1) (0,100) views (0,*) supervisor supervisee OwnerNo LeaseNo StaffNo PropertyNo ClientNo CommentVDate

21. EERD for Staff View of DreamHome BUSINESS OWNER STAFF PROPERTY PRIVATE OWNER LEASE CLIENT PREFERENCE holdassociate manage state register BOwn (1:1) (0,*) (1,1)(1,*) (0,1) (0,100) views (0,*) OwnerNo LeaseNo StaffNo PropertyNo ClientNo CommentVDate OWNER d SUPERVISOR

22. 22 Step 1 Build Local Conceptual Data Model for Each View Step 1.7 Check model for redundancy Objective: To check for the presence of any redundancy in the model. 1. Re-examine 1:1 relationships. 2. Remove redundant relationships. Step 1.8 Validate local conceptual model against user transactions Objective: To ensure that the local conceptual model supports the transactions required by the view. –Describe the transaction. –Use transaction pathways: diagrammatically represent the pathway taken by each transaction on the ERD. Conceptual DB Design

23. Using transaction’s Pathways BUSINESS OWNER STAFF PROPERTY PRIVATE OWNER LEASE CLIENT PREFERENCE holdassociate manage state register BOwn (1:1) (0,*) (1,1)(1,*) (0,1) (0,100) views (0,*) OwnerNo LeaseNo StaffNo PropertyNo ClientNo CommentVDate OWNER d SUPERVISOR (a) (e) (d) (h,i) (j) (l) (c,g) (m) (k) (b)

24. 24 Step 1 Build Local Conceptual Data Model for Each View Step1.9 Review local conceptual data model with user Objective: To review the local conceptual data model with the user to ensure that the model is a ‘true’ representation of the user’s view of the enterprise. Conceptual DB Design