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Unformatted text preview: Chapter Five – Data Modeling With The Entity-Relationship Model Page 5-1 ANSWERS TO REVIEW QUESTIONS 5.1 Describe the two phases in designing databases that arise from the development of new information systems. When developing new information systems, we first create a data model and then transform that data model into a database design. 5.2 In general terms, explain how a data model could be used to design a database for a small video rental store. The two steps of designing a database are: (1) creating a data model, in which we out the complexities of the database design, and (2) transforming the data model into a database design by adding database design features (these features, such as foreign keys, intersection tables for N:M relationships will be discussed in detail in Chapter 06) For a small video rental store, we would analyze the business requirements for the store to determine entities (such as EMPLOYEE, CUSTOMER, RENTAL, RENTAL_ITEM, ITEM) and the relationships between them. We would then create a database model. We would validate the model with the users at the store, and modify it until it meet the user’s needs and perceptions of how the store business operated. Once the database model was complete, we would transform it into a database design (described in Chapter 6), and finally create the database itself in the DBMS (Chapter 7). 5.3 Explain how a data model is like a building blueprint. What is the advantage of making changes during the data modeling stage? Before a building is actually constructed, it is carefully planned and designed. That work is documented in the building blueprint . Similarly, before a database is actually created in a DBMS, it needs to be carefully planned and designed. The work of planning and designing a database is documented in a data model . The advantage of making changes during the data modeling stage is that it is easier, simpler, faster and cheaper to make changes at that stage of database development. 5.4 Who is the author of the entity-relationship data model? Peter P. Chen [in his 1976 paper “the Entity-Relationship Model – Toward a Unified View of Data”] 5.5 Define entity. Give an example of an entity (other than one presented in this chapter). An entity is something that the users want to track, and is readily identifiable in their environment. We’ll use the example of a Real Estate Agency. Example entities are AGENT John Smith, PROPERTY 568 12 th Street, CASH_RECEIPT CR2004001. 5.6 Explain the difference between an entity class and an entity instance. An entity class is a collection of entities and is described by the structure or format of the entities in that class. An entity instance of an entity class is the representation of a particular entity, such as AGENT John Smith; it is described by the values of attributes of the entity. There are usually many instances of an entity in an entity class....
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This note was uploaded on 11/15/2011 for the course ECON 101 taught by Professor David during the Spring '11 term at Kwansei Gakuin University.
- Spring '11