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There may be a large number of good designs from which we must choose.  \nDatabase System Concepts-7th Edition 6.6 ©Silberschatz, Korth and Sudarshan  \n Design Approaches  \n▪ Entity Relationship Model (covered in this chapter)  \n• Models an enterprise as a collection of entities and relationships  \n▪ Entity: a “thing” or “object” in the enterprise that is distinguishable from other objects  \n• Described by a set of attributes  \n▪ Relationship: an association among several entities  \n• Represented diagrammatically by an entity-relationship diagram:  \n▪ Normalization Theory (Chapter 7)  \n• Formalize what designs are bad, and test for them  \nDatabase System Concepts-7th Edition 6.7 ©Silberschatz, Korth and Sudarshan  \nOutline of the ER Model  \nDatabase System Concepts-7th Edition 6.8 ©Silberschatz, Korth and Sudarshan  \nEntity Sets  \n▪ An entity is an object that exists and is distinguishable from other objects.  \n• Example: specific person, company, event, plant  \n▪ An entity set is a set of entities of the same type that share the same properties.  \n• Example: set of all persons, companies, trees, holidays  \n▪ An entity is represented by a set of attributes; i.e. , descriptive properties possessed by all members of an entity set.  \n• Example:  \ninstructor = (ID, name, salary )  \ncourse= (course_id, title, credits)  \n▪ A subset of the attributes form a primary key of the entity set; i.e. ,  \nuniquely identifying each member of the set.  \nDatabase System Concepts-7th Edition 6.10 ©Silberschatz, Korth and Sudarshan  \n Representing Entity sets in ER Diagram  \n▪ Entity sets can be represented graphically as follows:  \n• Rectangles represent entity sets.  \n• Attributes listed inside entity rectangle  \n• Underline indicates primary key attributes  \nDatabase System Concepts-7th Edition 6.12 ©Silberschatz, Korth and Sudarshan  \n Relationship Sets  \n▪ A relationship is an association among several entities  \nExample:  \n44553 (Peltier )  advisor 22222 ( Einstein)  \nstudent entity relationship set instructor entity  \n▪ A relationship set is a mathematical relation among n 􀁴 2 entities, each taken from entity sets  \n{(e1 , e2 ,…en) | e 1 􀂏 E1 , e2 􀂏 E2 ,…, en 􀂏 En}  \nwhere (e1 , e2 ,…, ","cbCaie8N6a9q9YpQ","https://ap.wps.com/l/cbCaie8N6a9q9YpQ","pdf",2598724,"English","# Design Phases\n## Initial phase: characterize data needs\n## Choosing a data model and conceptual schema\n## Describe operations and transactions\n## Final phase: logical and physical design\n# Design Alternatives\n## Redundancy pitfalls\n## Incompleteness pitfalls\n# Design Approaches\n## Entity Relationship Model\n## Normalization Theory (Chapter 7)\n# Outline of the ER Model\n## Entity Sets\n## Representing Entity Sets in ER Diagrams\n## Relationship Sets","[{\"question\":\"What are the main phases of database design described in Chapter 6?\",\"answer\":\"The chapter outlines an initial phase to characterize user data needs, a phase for choosing a data model and building a conceptual schema, a phase describing operations/transactions, and a final phase moving to implementation via logical design and physical design.\"},{\"question\":\"Why must redundancy and incompleteness be avoided in database schema design?\",\"answer\":\"Redundancy can cause repeated information and lead to data inconsistency across copies. Incompleteness makes it difficult or impossible to model certain aspects of the enterprise.\"},{\"question\":\"How do entity sets and primary keys relate to the ER model?\",\"answer\":\"An entity set groups entities of the same type sharing properties represented by attributes. A subset of these attributes forms a primary key that uniquely identifies each member of the entity set.\"}]","Chapter 6 - Database Design Using the E-R Model | PDF",1792965277,202]