Transcript S02L03_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
– Identify an entity relationship diagram (ERD)
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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!
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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.
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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.
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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?
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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.
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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.
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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.
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ERD for DJs on Demand
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Terminology
• Key terms used in this lesson include:
– Implementation-free
– Entity relationship diagram (ERD)
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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)
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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)
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new age (新世纪)
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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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