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Chapter 8

Chapter 8. Methodology - Conceptual Database Design. Chapter 15 in Textbook. Database Design. Hardware independent Software independent. Conceptual DB design. Hardware independent Software dependent. Logical DB design. Hardware dependent Software dependent. Physical DB design.

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Chapter 8

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

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

  3. 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.

  4. 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.

  5. 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.

  6. Methodology Overview – Logical Database Design for Relational Model • Step 2 Build and validate local logical data model for each view • 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.

  7. 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.

  8. 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.

  9. 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

  10. 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.

  11. Data Dictionary for Staff View ShowingDescription 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 PropertyForRentGeneral 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

  12. 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.

  13. ERD for Staff View of DreamHome supervisor supervise (0,*) STAFF register BUSINESS OWNER (0,*) supervisee (0,*) (1,*) (0,100) manage BOwn (0,1) (1:1) (0,1) PROPERTY views CLIENT (0,*) (0,*) POwn (0,1) (0,*) (0,*) (1:1) associate hold state (1,*) (1:1) (1:1) PRIVATE OWNER LEASE PREFERENCE (1:1)

  14. 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 SupervisesStaff 0..10 PropertyForRent 1..1 AssociatedWith Lease 0..*

  15. 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.

  16. 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.

  17. 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

  18. 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.

  19. ERD with PK StaffNo OwnerNo supervisor supervise (0,*) STAFF register BUSINESS OWNER (0,*) supervisee (0,*) (1,*) (0,100) manage PropertyNo VDate Comment BOwn (0,1) (1:1) (0,1) PROPERTY views CLIENT ClientNo (0,*) (0,*) POwn (0,1) (0,*) (0,*) (1:1) associate hold state OwnerNo (1,*) (1:1) (1:1) PRIVATE OWNER LEASE PREFERENCE LeaseNo (1:1)

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

  21. 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.

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

  23. 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.

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