C4 Relational Databases

• Database: a set of interrelated, centrally coordinated files

• DBMS (Database Management System): an interface between the database and applications

• Database system: the database + DBMS + applications

• DBA (Database administrator): person responsible for the database

• Schemas: the logical structure of database

• Conceptual-level: organization-wide view of the entire database

• External-level: a set of individual user views of portions of a database (subschema)

• Internal-level: low-level view; details about data storage

• Data dictionary: information about the structure of the database

• DBMS languages: DDL (definition), DML (manipulation), DQL (query), Report writer

• Relational Databases

• Data model: an abstract representation of the contents of a database

• Relational data model: database stored in tables (relations)

• Tuple: a row in a relation (entry)

• Primary key / Foreign key / Non-key

• If all data stored in one table

• Update anomaly, insert anomaly, delete anomaly, waste of space

• Requirements of a RD

1. All data single-valued
2. Primary keys not null
3. Foreign key values correspond to self-titled primary key
4. Non-keys describe characteristics identified by the primary key