Chapter 2 - Intro to relational model. Chapter 2 introduces the relational model of data, covering basic concepts such as the structure of relational databases, database schemas, keys, schema diagrams, relational query languages, and relational operations. | Chapter 2: Intro to Relational Model Database System Concepts, 6th Ed. ©Silberschatz, Korth and Sudarshan See for conditions on re-use Example of a Relation attributes (or columns) tuples (or rows) Database System Concepts - 6th Edition ©Silberschatz, Korth and Sudarshan Attribute Types The set of allowed values for each attribute is called the domain of the attribute Attribute values are (normally) required to be atomic; that is, indivisible The special value null is a member of every domain The null value causes complications in the definition of many operations Database System Concepts - 6th Edition ©Silberschatz, Korth and Sudarshan Relation Schema and Instance A1, A2, , An are attributes R = (A1, A2, , An ) is a relation schema Example: instructor = (ID, name, dept_name, salary) Formally, given sets D1, D2, . Dn a relation r is a subset of D1 x D2 x x Dn Thus, a relation is a set of n-tuples (a1, a2, , an) where each ai ∈ Di The current values (relation instance) of a relation are specified by a table An element t of r is a tuple, represented by a row in a table Database System Concepts - 6th Edition ©Silberschatz, Korth and Sudarshan Relations are Unordered Order of tuples is irrelevant (tuples may be stored in an arbitrary order) Example: instructor relation with unordered tuples Database System Concepts - 6th Edition ©Silberschatz, Korth and .
