cs411-02-er - CS411 Database Systems 02: ER Model 1 The New...

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1 CS411 Database Systems 02: ER Model
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2 The New Contract on Lecture: Students • Students: – Please attend class and participate. – Please sit in the front rows so we are together. – Please interact with instructor (signal, ask, answer). – Please do not fall asleep or …
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3 The New Contract on Lecture: Instructor • Instructor: – Will be do my best to prepare. – Will respect each question. – Will not rush to cover all the materials. – Will make sure online students hear well. – Will not fall asleep or …
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Why Do We Learn This? 4
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5 Steps in Building a DB Application • Suppose you are working on CS411 project • Step 0: pick an application domain – we will talk about this later • Step 1: conceptual design – discuss with your team mates what to model in the application domain – need a modeling language to express what you want – ER model is the most popular such language – output: an ER diagram of the app. domain
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6 Steps in Building a DB Application • Step 2: pick a type of DBMS – relational DBMS is most popular and is our focus • Step 3: translate ER design to a relational schema – use a set of rules to translate from ER to rel. schema – use a set of schema refinement rules to transform the above rel. schema into a good rel. schema • At this point – you have a good relational schema on paper
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7 Steps in Building a DB Application • Subsequent steps include – implement your relational DBMS using a "database programming language" called SQL – ordinary users cannot interact with the database directly – and the database also cannot do everything you want – hence write your application program in C++, Java, Perl, etc to handle the interaction and take care of things that the database cannot do • So, the first thing we should start with is to learn ER model . ..
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8 ER Model • Gives us a language to specify – what information the db must hold – what are the relationships among components of that information • Proposed by Peter Chen in 1976 • What we will cover –bas ic s tuff
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9 address name ssn Person buys makes employs Company Product name category stockprice name price Basic Concepts
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10 Entities and Attributes • Entities – real-world objects distinguishable from other objects – described using a set of attributes • Attributes – each has an atomic domain: string, integers, reals, etc. • Entity set: a collection of similar entities Product name category price Company stockprice name
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11 Relations • A mathematical definition: – if A, B are sets, then a relation R is a subset of A x B • A={1,2,3}, B={a,b,c,d}, R = {(1,a), (1,c), (3,b)} makes is a subset of Product x Company : 1 2 3 a b c d A= B= makes Company Product
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12 address name ssn Person buys makes employs Company Product name category stockprice name price ER Diagram
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13 More about relationships . ..
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This note was uploaded on 02/17/2012 for the course CS 411 taught by Professor Winslett during the Spring '07 term at University of Illinois at Urbana–Champaign.

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cs411-02-er - CS411 Database Systems 02: ER Model 1 The New...

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