tailieunhanh - Lecture Database System: Chapter 7 - Functional Dependencies

Chapter 7 - Functional Dependencies includes Informal Design Guidelines for Relational Databases (Semantics of the Relation Attributes, Redundant Information in Tuples and Update Anomalies, Null Values in Tuples, Spurious Tuples), Functional Dependencies (FDs). | CSC271 Database Systems Lecture # 7 Summary: Previous Lecture Relational keys Integrity constraints Views The Relational Algebra and Relational Calculus Chapter 4 Introduction Relational algebra and relational calculus are formal languages associated with the relational model Informally, relational algebra is a (high-level) procedural language and relational calculus a non-procedural language However, formally both are equivalent to one another A language that produces a relation that can be derived using relational calculus is said to be relationally complete Relational Algebra Relational algebra operations work on one or more relations to define another relation without changing the original relations Both operands and results are relations, so output from one operation can become input to another operation Allows expressions to be nested, just as in arithmetic is called closure property Relational Algebra Operations Five basic operations in relational algebra: Selection, Projection, Cartesian product, Union, and Set Difference These perform most of the data retrieval operations needed Also have Join, Intersection, and Division operations, which can be expressed in terms of five basic operations Unary vs. binary operations Relational Algebra Operations Relational Algebra Operations Instance of Sample Database Instance of Sample Database Instance of Sample Database Selection (Restriction) predicate (R) Works on a single relation R and defines a relation that contains only those tuples (rows) of R that satisfy the specified condition (predicate) More complex predicate can be generated using the logical operators ∧ (AND),∨ (OR) and ~ (NOT) Example: Selection (Restriction) List all staff with a salary greater than £10,000 salary > 10000 (Staff) Projection a1, a2. . . , an(R) Works on a single relation R and defines a relation that contains a vertical subset of R, extracting the values of specified attributes and eliminating duplicates Example: Projection . | CSC271 Database Systems Lecture # 7 Summary: Previous Lecture Relational keys Integrity constraints Views The Relational Algebra and Relational Calculus Chapter 4 Introduction Relational algebra and relational calculus are formal languages associated with the relational model Informally, relational algebra is a (high-level) procedural language and relational calculus a non-procedural language However, formally both are equivalent to one another A language that produces a relation that can be derived using relational calculus is said to be relationally complete Relational Algebra Relational algebra operations work on one or more relations to define another relation without changing the original relations Both operands and results are relations, so output from one operation can become input to another operation Allows expressions to be nested, just as in arithmetic is called closure property Relational Algebra Operations Five basic operations in relational algebra: Selection, .