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ER Diagrams Notes.docx

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Computer Science
Computer Science 1032A/B

ER Diagrams E-R Symbols: Entities: rectangles • Each entity has a unique ID number (primary key) • Name, location etc. Attributes: ovals • Key attributes o Uniquely identifies an entity or relationship o Identified by being underlined Relationships: diamonds • Each relationship has 3 properties o Attributes  Ovals  Key attribute - If unique, underline (social insurance number)  Ex: social security number o Cardinality  How much of one entity is related to other entity?  Write that number on top, write M for many, N= many to many  Cannot have M to M – have to have M to N o Participation  Is everyone of this particular entity is related to the other entity?  Single line  represents partial participation  Double line  represents total participation Example: Faculty would be in a rectangle, is a chair of would be in a diamond, and department would be in a rectangle Designing an E-R Diagram: 1. Collect and review ALL the data 2. Identify entities and attributes and draw them on your ER diagram 3. Identify the key attributes and underline them on your diagram 4. Decide on the relationships and draw lines between the entities, including any attributes of the relationships 5. Decide on the car
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