tailieunhanh - Database System: Chapter 7 - Functional Dependencies

Database System: 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). | Chapter 7 Functional Dependencies Copyright © 2004 Pearson Education, Inc. 5/14/2020 4:10:15 AM Outline 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) Definition of FD Inference Rules for FDs Equivalence of Sets of FDs Minimal Sets of FDs Slide 7 - Informal Design Guidelines for Relational Databases (1) What is relational database design? The grouping of attributes to form "good" relation schemas Two levels of relation schemas The logical "user view" level The storage "base relation" level Design is concerned mainly with base relations What are the criteria for "good" base relations? Slide 7 - Informal Design Guidelines for Relational Databases (2) We first discuss informal guidelines for good relational design Then we discuss formal concepts of functional dependencies and normal forms - 1NF (First Normal . | Chapter 7 Functional Dependencies Copyright © 2004 Pearson Education, Inc. 5/14/2020 5:23:41 AM Outline 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) Definition of FD Inference Rules for FDs Equivalence of Sets of FDs Minimal Sets of FDs Slide 7 - Informal Design Guidelines for Relational Databases (1) What is relational database design? The grouping of attributes to form "good" relation schemas Two levels of relation schemas The logical "user view" level The storage "base relation" level Design is concerned mainly with base relations What are the criteria for "good" base relations? Slide 7 - Informal Design Guidelines for Relational Databases (2) We first discuss informal guidelines for good relational design Then we discuss formal concepts of functional dependencies and normal forms - 1NF (First Normal Form) - 2NF (Second Normal Form) - 3NF (Third Normal Form) - BCNF (Boyce-Codd Normal Form) Additional types of dependencies, further normal forms, relational design algorithms by synthesis are discussed in Chapter 11 Slide 7 - Semantics of the Relation Attributes GUIDELINE 1: Informally, each tuple in a relation should represent one entity or relationship instance. (Applies to individual relations and their attributes). Attributes of different entities (EMPLOYEEs, DEPARTMENTs, PROJECTs) should not be mixed in the same relation Only foreign keys should be used to refer to other entities Entity and relationship attributes should be kept apart as much as possible. Bottom Line: Design a schema that can be explained easily relation by relation. The semantics of attributes should be easy to interpret. Slide 7 - A simplified COMPANY relational database schema Slide 7 - Redundant Information in Tuples and Update Anomalies Mixing attributes of multiple entities may cause problems .