IFB130 Lecture Notes - Lecture 4: Logical Data Model, Relational Model, Foreign Key
19 Oct 2018
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Document Summary
Logical data model: all data is represented in terms of tuples (rows), grouped into relations (tables, a database organised in terms of the relational model is a relational database. Structure of a relation: relation is a table with columns and rows, attribute is a named column of a relation, tuple is a row of a relation. Schema is a representation of a plan in the form of an outline or model: conceptual model = conceptual schema. Set of relation schemas, each with a distinct name: relationships, foreign keys, constraints and domains are also described. The set of allowable values for one or more attributes. A role might only be allowed [manager, administrator, clerk] The degree of a relation is the number of attributes (columns) it contains. Super key: any combination of columns that uniquely identifies a row in a table. Candidate key: a minimal super key, meaning no proper subset within the relation is a super key.
