* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Database System Concepts, 6 th Ed
Survey
Document related concepts
Extensible Storage Engine wikipedia , lookup
Open Database Connectivity wikipedia , lookup
Serializability wikipedia , lookup
Entity–attribute–value model wikipedia , lookup
Oracle Database wikipedia , lookup
Registry of World Record Size Shells wikipedia , lookup
Ingres (database) wikipedia , lookup
Functional Database Model wikipedia , lookup
Microsoft Jet Database Engine wikipedia , lookup
Concurrency control wikipedia , lookup
Relational model wikipedia , lookup
Clusterpoint wikipedia , lookup
Transcript
Chapter 7: Entity-Relationship Model Database System Concepts, 6th Ed. ©Silberschatz, Korth and Sudarshan See www.db-book.com for conditions on re-use Chapter 7: Entity-Relationship Model Design Process Modeling Constraints E-R Diagram Design Issues Weak Entity Sets Extended E-R Features Design of the Bank Database Reduction to Relation Schemas Database Design UML Database System Concepts - 6th Edition 7.2 ©Silberschatz, Korth and Sudarshan Modeling An entity is an object Example: specific person, company Entities have attributes Example: Entity: person Attributes: name, addresse Database System Concepts - 6th Edition 7.3 ©Silberschatz, Korth and Sudarshan Entities instructor and student instructor_ID instructor_name Database System Concepts - 6th Edition student-ID student_name 7.4 ©Silberschatz, Korth and Sudarshan Relationship Sets A relationship is an association between entities Example: 44553 (Peltier) student entity Database System Concepts - 6th Edition advisor relationship 7.5 22222 (Einstein) instructor entity ©Silberschatz, Korth and Sudarshan Relationship advisor Database System Concepts - 6th Edition 7.6 ©Silberschatz, Korth and Sudarshan Degree of a Relationship Set binary relationship involve two entity sets (or degree two). Database System Concepts - 6th Edition 7.7 ©Silberschatz, Korth and Sudarshan Attributes Example: instructor = (ID, name, street, city, salary ) course= (course_id, title, credits) Attribute types: Simple and composite attributes. Database System Concepts - 6th Edition 7.8 ©Silberschatz, Korth and Sudarshan Composite Attributes Database System Concepts - 6th Edition 7.9 ©Silberschatz, Korth and Sudarshan Mapping Cardinality Constraints For a binary relationship set the mapping cardinality must be one of the following types: One to one One to many Many to one Many to many Database System Concepts - 6th Edition 7.10 ©Silberschatz, Korth and Sudarshan Mapping Cardinalities One to many One to one Database System Concepts - 6th Edition 7.11 ©Silberschatz, Korth and Sudarshan Mapping Cardinalities Many to one Database System Concepts - 6th Edition Many to many 7.12 ©Silberschatz, Korth and Sudarshan E-R Diagrams Database System Concepts - 6th Edition 7.13 ©Silberschatz, Korth and Sudarshan Relationship Sets with Attributes Database System Concepts - 6th Edition 7.14 ©Silberschatz, Korth and Sudarshan Cardinality Constraints () : “one,” (—): “many,” Database System Concepts - 6th Edition 7.15 ©Silberschatz, Korth and Sudarshan One-to-One Relationship one-to-one relationship between an instructor and a student Database System Concepts - 6th Edition 7.16 ©Silberschatz, Korth and Sudarshan One-to-Many Relationship one-to-many relationship between an instructor and a student Database System Concepts - 6th Edition 7.17 ©Silberschatz, Korth and Sudarshan Many-to-One Relationships In a many-to-one relationship between an instructor and a student, Database System Concepts - 6th Edition 7.18 ©Silberschatz, Korth and Sudarshan Many-to-Many Relationship Database System Concepts - 6th Edition 7.19 ©Silberschatz, Korth and Sudarshan How about doing an ER design interactively on the board? Suggest an application to be modeled. Database System Concepts, 6th Ed. ©Silberschatz, Korth and Sudarshan See www.db-book.com for conditions on re-use Weak Entity Sets An entity set that does not have a primary key is referred to as a weak entity set. The existence of a weak entity set depends on the existence of a identifying entity set It must relate to the identifying entity set via a total, one-to-many relationship set from the identifying to the weak entity set Identifying relationship depicted using a double diamond The discriminator (or partial key) of a weak entity set is the set of attributes that distinguishes among all the entities of a weak entity set. The primary key of a weak entity set is formed by the primary key of the strong entity set on which the weak entity set is existence dependent, plus the weak entity set’s discriminator. Database System Concepts - 6th Edition 7.21 ©Silberschatz, Korth and Sudarshan Weak Entity Sets (Cont.) We underline the discriminator of a weak entity set with a dashed line. We put the identifying relationship of a weak entity in a double diamond. Primary key for section – (course_id, sec_id, semester, year) Database System Concepts - 6th Edition 7.22 ©Silberschatz, Korth and Sudarshan Weak Entity Sets (Cont.) Note: the primary key of the strong entity set is not explicitly stored with the weak entity set, since it is implicit in the identifying relationship. If course_id were explicitly stored, section could be made a strong entity, but then the relationship between section and course would be duplicated by an implicit relationship defined by the attribute course_id common to course and section Database System Concepts - 6th Edition 7.23 ©Silberschatz, Korth and Sudarshan Extended ER Features Database System Concepts - 6th Edition 7.24 ©Silberschatz, Korth and Sudarshan Extended E-R Features: Specialization Top-down design process; A triangle component labeled ISA (E.g., instructor “is a” person). Attribute inheritance Database System Concepts - 6th Edition 7.25 ©Silberschatz, Korth and Sudarshan Specialization Example Database System Concepts - 6th Edition 7.26 ©Silberschatz, Korth and Sudarshan Extended ER Features: Generalization A bottom-up design process Specialization and generalization are represented in an E-R diagram in the same way. Database System Concepts - 6th Edition 7.27 ©Silberschatz, Korth and Sudarshan End of Chapter 7 Database System Concepts, 6th Ed. ©Silberschatz, Korth and Sudarshan See www.db-book.com for conditions on re-use