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Entity Relationship Modeling and ERDs

Entity Relationship Modeling and ERDs. What Will I Learn?. In this lesson, you will learn to: Define the meaning of implementation-free as it relates to data models and database design implementation List the four goals of entity relationship modeling

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Entity Relationship Modeling and ERDs

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  1. Entity Relationship Modeling and ERDs

  2. What Will I Learn? • In this lesson, you will learn to: • Define the meaning of implementation-free as it relates to data models and database design implementation • List the four goals of entity relationship modeling • Identify an entity relationship diagram (ERD)

  3. Why Learn It? • An entity relationship diagram, abbreviated as ERD, is a consistent tool that can be used to represent data requirements regardless of what type of database is used, or even if a database is used at all!

  4. implementation-free • A good conceptual data model stays the same regardless of what type of database the system is eventually built on. • This is what is mean when we say that the model is “implementation-free.” • The data model should stay the same even if a database is not used at all, • for example if the data is eventually stored as pieces of paper in a filing cabinet.

  5. The four goals of ER modeling • The four goals of ER modeling: • Capture all required information • Ensure that information appears only once • Model no information that is derivable from other information already modeled • Locate information in a predictable, logical place • Think of your school record. From your first days in school, data about you was captured. There is probably a record of your absences, notes on discipline, classes taken, and grades earned.

  6. DJs on Demand • Read the complete business scenario for the DJ business below. Then examine the completed ERD. We started out as a group of friends who organized parties and customized our own music. Then we thought we’d turn it into a business to pursue our interests and earn some money. We called ourselves the “DJs on Demand.” Everyone who works here is a partner. Every partner has a specific responsibility. The project manager makes the first contact with the client to discuss the event. Is it a birthday party, a wedding, an anniversary, a graduation? What is the date for the party or event?

  7. DJs on Demand Once that’s decided, the event planner gets in touch with the client about specific locations, catering, decorations, and other specific details. The DJ talks with the client about the kind of music wanted. The project manager supervises the event planners and DJs. He/she also authorizes expenditures related to a project. We have a large collection of CDs. Each CD contains several songs, and the same song can appear on several CDs. We like to classify each song by type (hip hop, salsa, R & B (rhythm and blues), techno, salsa, polka, rock, jazz, new age, classical, etc.) We can propose an initial list of songs to the client depending on the event. Of course, a client can request other songs as well.

  8. DJs on Demand Our client list is growing. We have a lot of repeat business -- customers who like what we’ve done and ask us to work their other events. We have some very busy customers who can have more than one event going on at the same time! We also have a list of themes that we can use to categorize these events. For example: a wedding may have a tropical theme, a party may have a carnival theme, an anniversary could have a sixties theme, etc. This helps us pick a venue and also gives us an idea of what the DJ (and other musicians) should wear. Some partners have a specialty or expertise -- so a theme can also help us assign the right person to the job.

  9. DJs on Demand Events are held either in a public space or a private home. The event manager visits both and makes arrangements with the public-space renter or the private-home owner. Since several partners can work on an event, and an event can be assigned to several partners, we like to keep track of who is working on which event. We keep a log of what each event planner and DJ has done on an event, and when they did it.

  10. ERD for DJs on Demand

  11. Terminology • Key terms used in this lesson include: • Implementation-free • Entity relationship diagram (ERD)

  12. Summary • In this lesson, you have learned how to: • Define the meaning of implementation-free as it relates to data models and database design implementation • List the four goals of entity relationship modeling • Identify an entity relationship diagram (ERD)

  13. Some new words customized (定制, 用户化) partner (合伙人, 股东, 舞伴, 伴侣) anniversary (周年纪念) catering (公共饮食业; 给养) project manager (项目管理人[经理]) authorizes (批准) Rock (Rock 'n' roll.【音乐】 摇滚乐) R & B (rhythm and blues)节奏和布鲁斯 jazz(20世纪产生于美国的一种舞曲性音乐)爵士乐, 喧闹 hip hop (希普霍普（由快板歌、涂墙艺术、霹雳舞等构成的亚文化）) salsa (拉丁舞) polka (波尔卡舞, 女用紧身短上衣) new age (新世纪)

  14. Some new words tropical (热带的, 热情的) carnival (狂欢节) venue (会议地点) specialty (专业) expertise (技术专长) renter (租贷人) soundtracks (电影的配乐/声道；音带) Qualifies (限制修饰) Classifies (分类, 分等) Mandatory(命令的, 强制的) double check n.仔细的检查 Oatmeal ((燕)麦片, (燕)麦粥) raisin (葡萄干)

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