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Database Design Design method

Database Design Design method. John Wordsworth Department of Computer Science The University of Reading J.B.Wordsworth@rdg.ac.uk Room 129, Ext 6544. Lecture objectives. To provide an overview of the design process

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Database Design Design method

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  1. Database DesignDesign method John Wordsworth Department of Computer Science The University of Reading J.B.Wordsworth@rdg.ac.uk Room 129, Ext 6544 2/CS/3X

  2. Lecture objectives • To provide an overview of the design process • To explain the terms conceptual design, logical design and physical design as applied to database 2/CS/3X

  3. Overview of the design process • Step 1: Conceptual database design • Understand what’s there; for the moment don’t worry about database theory or the technology • Steps 2 and 3: Logical database design • Transform the conceptual design into one that is theoretically sound • Step 4 to 9: Physical database design • Transform the logical design into one that works with the chosen technology 2/CS/3X

  4. Step 1: Conceptual database design • 1.1 Identify entity types. • 1.2 Identify relationship types. • 1.3 Identify and associate attributes with entity types. • 1.4 Determine attribute domains. • 1.5 Determine candidate keys and primary keys. • 1.6 Consider use of enhanced modelling concepts. • 1.7 Check model for redundancy. • 1.8 Validate local conceptual model against user transactions. • 1.9 Review conceptual data model with users. 2/CS/3X

  5. Steps 2 and 3: Logical database design • Step 2: Build and validate logical data models for each view. 2/CS/3X

  6. Step 2.1 Remove features not compatible with the relational model (1) Remove many-many binary relationships. (2) Remove many-many recursive relationships. (3) Remove complex relationships. (4) Remove multivalued attributes. 2/CS/3X

  7. Step 2.2 Derive relations for logical data model (1) Strong entity types. (2) Weak entity types. (3) One-many binary relationship types. (4) One-one binary relationship types. (5) One-one recursive relationships (6) Super/subclass relationship types. (7) Many-many binary relationship types. (8) Complex relationship types. (9) Multivalued attributes 2/CS/3X

  8. Step 2.3 Validate by normalisation • First normal form removes repeating groups. • Second normal form removes partial dependencies on the primary key. • Third normal form removes transitive dependencies. • Boyce-Codd normal form removes remaining anomalies from functional dependencies. 2/CS/3X

  9. Validation of local LDM • Step 2.4 Validate relations against user transactions • Step 2.5 Define integrity constraints • Required data • Attribute domain constraints • Entity integrity • Referential integrity • Enterprise constraints (= business rules) • Step 2.6 Review local logical data model with user 2/CS/3X

  10. Referential integrity • (1) Insert a tuple into a child relation. • (2) Delete tuple from child relation. • (3) Update foreign key of child tuple. • (4) Insert tuple into parent relation. • (5) Delete tuple from parent relation • No action • Cascade • Set null • Set default • No check • (6) Update primary key of parent relations 2/CS/3X

  11. Step 3.1 Merge local LDMs in to Global LDM • Review names and contents of entities (relations) and their candidate keys. • Review names and contents of relationships and foreign keys. • Merge entities from local models. • Include entities unique to each local model. • Merge relationships from local models. • Include relationships unique to each local model. • Check for missing entities and relationships. • Check foreign keys. • Check integrity constraints. • Draw the global E-R diagram. • Update the documentation. 2/CS/3X

  12. Rest of step 3 • 3.2 Validate global logical data model • 3.3 Check for future growth • 3.4 Review global logical data model with users. 2/CS/3X

  13. Steps 4 to 9Physical database design • Step 4: Translate global LDM for target DBMS • Step 5: Design physical representation • Step 6: Design user views • Step 7: Design security mechanisms • Step 8: Consider introducing controlled redundancy • Step 9: Monitor and tune the operational system. 2/CS/3X

  14. Step 4: Translate LDM for target DBMS • Step 4.1 Design base relations • Step 4.2 Design representation of derived data. • Step 4.3 Design the enterprise constraints for target DBMS 2/CS/3X

  15. Step 5: Design physical representation (1) • Step 5.1 Analyze transactions • frequency of transaction • what relations and attributes are accessed • what is the type of access (query, insert, update, delete) • Note: if an attribute is updated, take care if it is to be included in a secondary index) • care with attributes used in predicates (WHERE), and the type of predicates (possible candidate for access structures (indexes)) • care with attributes used in joins (candidates for access structures) • time constraints 2/CS/3X

  16. Design physical representation: 2 • Step 5.2 Choose file organizations • DMBS may or may not give you authority in this matter • Step 5.3 Choose secondary indexes • DBMS should give you authority here • Step 5.4 Estimate disk space requirements 2/CS/3X

  17. Security and tuning • Step 6: Design user views • Step 7: Design security mechanisms • Step 6.1 Design user views • Step 6.2 Design access rules • Step 8: Consider the introduction of controlled redundancy • Step 9: Monitor and tune the operational system 2/CS/3X

  18. Key points • Conceptual design creates a number of entity-relationship models of the data. • Logical design merges the conceptual models, and creates a relational model. • Physical design organises the data on physical hardware devices. 2/CS/3X

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