Chapter 4 High-level Database Models Entity/Relationship Models (E/R diagram) Unified Modeling Language (UML) Object Definition Language (ODL) Hot to Transfer them to a relational model 1
1 Chapter 4 High-level Database Models Entity/Relationship Models (E/R diagram) Unified Modeling Language (UML) Object Definition Language (ODL) Hot to Transfer them to a relational model
Introduction ▣现实世界：客观存在的世界。 ▣信息世界：现实世界在人们头脑中的反映。 ▣机器世界：信息世界的信息在机器世界中以数据的形 式存放。 reality-》information world-》machine world E-R data model relational model√ UML object-relational model ODL object-oriented model 2
2 Introduction 现实世界：客观存在的世界。 信息世界：现实世界在人们头脑中的反映。 机器世界：信息世界的信息在机器世界中以数据的形 式存放。 reality - 》information world- 》 machine world E-R data model relational model √ UML object-relational model ODL object-oriented model
Purpose of E/R Model The E/R model allows us to sketch database schema designs. Includes some constraints,but not operations. Designs are pictures called entity- relationship diagrams. Later:convert E/R designs to relational DB designs. 3
3 Purpose of E/R Model The E/R model allows us to sketch database schema designs. Includes some constraints, but not operations. Designs are pictures called entityrelationship diagrams. Later: convert E/R designs to relational DB designs
Framework for E/R Design is a serious business. The "boss"knows they want a database,but they don't know what they want in it. Sketching the key components is an efficient way to develop a working database
4 Framework for E/R Design is a serious business. The “boss ” knows they want a database, but they don ’t know what they want in it. Sketching the key components is an efficient way to develop a working database
Entity/Relationship Model Entity like objects,=things Entity set like class set of similar Entity or objects Attribute=property of entities in an entity set,similar to fields of a struct. Relation=connect two or more entity set In diagrams, entity set rectangle; attribute:oval, relation:diamonds 5
5 Entity/Relationship Model Entity like objects, =things Entity set like class = set of similar Entity or objects Attribute=property of entities in an entity set, similar to fields of a struct. Relation=connect two or more entity set In diagrams, entity set : rectangle; attribute: oval, relation: diamonds