Database vs File System Integrated Data Reduced Data Duplication Program/Data Independence Easier representation for user Separate/Isolated data Appl. Program Dependency Incompatible files Difficult representation for user

Database Self describing Data dictionary Metadata Is a model of the user’s model Relational model--from PCs to Mainframe Schema

Data Modeling (ERD) Entity Attributes Identifiers Relationships –Usually binary (degree two) –1:1, 1:N, M:N

ERD Cardinality Weak (dependent) entities ID-Dependent Entities Supertype/subtype –Parent/child –Is-A instead of Has-A –Generalization/specialization; inheritance

Relational Model and Normalization Definitions –rows, columns, etc. Normalization –purpose –1NF, 2NF, 3NF, BCNF, 4NF –determinants/dependencies –keys

Domain/Key Normal Form Break into themes and use common sense –test all business constraints against keys and domain

Database Design ID-dependent (weak) entities require key of both parent and key of entity Has-A relationships –1:1 relationship foreign key can go either way –1:N relationship Foreign key must go in the –M:N relationship requires an associative entity (intersection or link table) with 1:M and M:1

Database Design Recursive Relationships –1:1 similar to Has-A but in one relation –1:M One table with the one row representing the parent and child rows added with parent foreign key –M:N requires link or intersection relation with all pairs to augment the single relation with attribute data