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ER Models and Diagrams

by: Emily McIlhattan

ER Models and Diagrams MGMT 382

Emily McIlhattan
GPA 3.72
Management Information Systems
Dr. Dejoie

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About this Document

These lectures goes over models and diagrams for entity-relationship, which goes with project 2
Management Information Systems
Dr. Dejoie
Class Notes
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This 3 page Class Notes was uploaded by Emily McIlhattan on Thursday February 19, 2015. The Class Notes belongs to MGMT 382 at Purdue University taught by Dr. Dejoie in Winter2015. Since its upload, it has received 444 views. For similar materials see Management Information Systems in Business, management at Purdue University.

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Date Created: 02/19/15
MGMT 382 ER Modeling Current Lecture ER Model a What should an entity be i Nouns ii Object with many instances in the database iii Object composed of multiple attributes iv Object we are trying to model b NOT be i User of database ii Output of database system report 1 ARl just an outcome c ldenti erkey unique attribute or combination of attributes that identi es individual instances of an entity type d Candidate key attribute that could be a key satis es the requirements for being a key ID for purdue Social security number e Composite 2 attribute elds using rst and last name in 382 vs simple key 1 key i Policy can dictate what key is used Characteristics a Wont change in value no inconsistency b Wont be null c No intelligent identi ers know value l tells us something about that person adding WL to student id number d Substitute new simple keys for long composite keys Numeric always talking about maximum a Cardinality of relationship i Onetoone each entity in the relationship will have exactly one related entity 1 student per car purdue ii Onetomany an entity on oneside of the relationship can have many realted entities but an entity on other side will have a maximum of one realted entity one student can register 1 cars at purdue iii Manytomanyentities on both sides of the relationship can have many related entities on the other side 1 Studentmany cars l any car can be registered by many students Constraints instances of one entity that can or must be associated with instance of another entity a Minimum cardinality i 0 optional l conmayif you want ii 1 mandatory hard you must 1 Max ER Diagrams a Upright Rectangle Registers relationship verbs There are two relationships going on here Student D Car Car D student Always jump over relationship on opposite side Onetoone and onetomany always has foreign key which is a link Next Lecture School Location Phone School ID Department Department Q Room Student ID Course Course Description 12995 rtment D Student Stude ntID Name Address The CourseStudent is an associative entity only when there is a many to many relationship has attributes and links entities together serves both as an entity and relationship simultaneously all Associative entities could have meaning independent of other entities relationships for AE should be many also should be in a rounded rectangle


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