C4 Relational Databases
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Database: a set of interrelated, centrally coordinated files
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DBMS (Database Management System): an interface between the database and applications
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Database system: the database + DBMS + applications
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DBA (Database administrator): person responsible for the database
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Schemas: the logical structure of database
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Conceptual-level: organization-wide view of the entire database
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External-level: a set of individual user views of portions of a database (subschema)
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Internal-level: low-level view; details about data storage
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Data dictionary: information about the structure of the database
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DBMS languages: DDL (definition), DML (manipulation), DQL (query), Report writer
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Relational Databases
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Data model: an abstract representation of the contents of a database
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Relational data model: database stored in tables (relations)
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Tuple: a row in a relation (entry)
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Primary key / Foreign key / Non-key
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If all data stored in one table
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Update anomaly, insert anomaly, delete anomaly, waste of space
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Requirements of a RD
- All data single-valued
- Primary keys not null
- Foreign key values correspond to self-titled primary key
- Non-keys describe characteristics identified by the primary key
