Chapter 8 Methodology Conceptual Database Design Chapter 15

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 Conceptual DB Design 2

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 3

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 4

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. 5

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. Conceptual DB Design 6

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 7

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. 8

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 9

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 10

Data Dictionary for Staff View Showing Description of Entities Entity Name Staff Description General term describing all staff employed by Dearm. Home Property. For. Rent General term describing all property for rent Conceptual DB Design Aliases Employee Property Occurrence Each member of staff works at one particular branch Each property has a single owner & 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 11

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 12

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

Data Dictionary for Staff View Showing Description of Relationships Entity Name Multiplicity Relationship Entity Name Multiplicity Staff 0. . 1 Manages Supervises Property. For. Rent Staff 0. . 100 0. . 10 Property. For. Rent 1. . 1 Associated. With Lease 0. . * Conceptual DB Design 14

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 15

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 16

Data Dictionary for Staff View Showing Description of Attributes Entity Attribute Name Staff. No Description Data Length Nulls Multi- Default Type Valued Value Uniquely identifies a staff member varchar 5 No No Range PK 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 DOB Date of Birth of member of staff Date Yes No Conceptual DB Design M F, M 1960 -1990 17

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 18

ERD with PK Staff. No Owner. No supervisor BUSINESS OWNER (1, *) supervise (0, *) supervisee (0, *) STAFF register (0, *) (0, 100) manage Property. No BOwn (0, 1) POwn (0, 1) PROPERTY VDate (0, *) (1, *) PRIVATE OWNER LEASE (0, *) (1: 1) CLIENT (0, *) hold (1: 1) Lease. No views (0, *) associate Owner. No Comment (1: 1) state (1: 1) PREFERENCE Client. No

EERD for Staff View of Dream. Home Staff. No SUPERVISOR STAFF register (0, *) (0, 100) manage Owner. No Property. No (1, *) OWNER (1, 1) BOwn (0, 1) PROPERTY VDate (0, *) views (0, *) d PRIVATE OWNER hold (1: 1) Lease. No LEASE (0, *) (1: 1) CLIENT (0, *) associate BUSINESS OWNER Comment (1: 1) state (1: 1) PREFERENCE Client. No

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 21

Using transaction’s Pathways Staff. No (b) SUPERVISOR STAFF (a) register (0, *) (0, 100) (e) (d) manage Owner. No Property. No (0, 1) (c, g) (1, *) OWNER (1, 1) BOwn PROPERTY VDate (0, *) d PRIVATE OWNER (l) LEASE (k) (j) (1: 1) (0, *) (1: 1) Client. No CLIENT (0, *) hold (1: 1) Lease. No views (h, i) associate BUSINESS OWNER Comment (1: 1) state (m) (1: 1) PREFERENCE

Step 1 Build Local Conceptual Data Model for Each View Step 1. 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 23