3024-Chap9

# 3024-Chap9 - 9 CONCEPTUAL DATA MODELING ENTITY-RELATIONSHIP...

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9. CONCEPTUAL DATA MODELING: ENTITY-RELATIONSHIP DIAGRAMS Entity-Relationship (E-R) Model = conceptual data model where entity classes, attributes, relationships, and onstraints (e g cardinality) are modeled graphically constraints (e.g., cardinality) are modeled graphically. • one or more E-R diagrams Let’s examine E-R modeling constructs and rules, in the context of Anna’s Books. We’ll also show the E-R representation of the conceptual schema for JA Machining. 2010 John P. Shewchuk ISE 3024 Course Notes 9 – 1

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9.1 Basic Entity-Relationship Concepts 9.1.1 Entity Classes and Attributes Modeling of entity classes and attributes: Entity classes: Attributes: Attributes (ovals) connected to corresponding entity classes (rectangles) with undirected lines. Additional attribute characteristics (key, multivalued ttributes etc ) also modeled 2010 John P. Shewchuk ISE 3024 Course Notes 9 – 2 attributes, etc.) also modeled.
.g., E- diagrams for ustomer nd upplier firstName lastName Key attribute e.g., E R diagrams for Customer and Supplier : ame Customer Entity Class Supplier name address Composite Attribute phone rating state street city state zip Attribute Multivalued Component Attribute Attribute 2010 John P. Shewchuk ISE 3024 Course Notes 9 – 3

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9.1.2 Relationship Types and Constraints Modeling of relationship types and constraints: Relationship types: Relationship attributes: Relationship type (diamond) connects two associated ntity classes (rectangles) via undirected lines entity classes (rectangles) via undirected lines. Attributes connected to associated relationship type. Cardinality ratio, min/max and participation constraints lso modeled 2010 John P. Shewchuk ISE 3024 Course Notes 9 – 4 also modeled.
g E- diagram for ook AvailableFrom Supplier e.g., E R diagram for Book AvailableFrom Supplier : Relationship Type Reverse Relationship Type Name Cardinality CanProvide Ratio Book Supplier Available From (0 .. M) (2 .. N) N M ntity price Optional Participation Mandatory Participation Min/Max Cardinality Entity Class Relationship Type Attribute 2010 John P. Shewchuk ISE 3024 Course Notes 9 – 5

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9.2 Constructing E-R Diagrams In the last chapter, we developed the conceptual schema r Anna’s Books for Anna s Books. We articulated the schema tabularly. What would this same schema look like as an E-R iagram? daga 2010 John P. Shewchuk ISE 3024 Course Notes 9 – 6
itial E- diagram: Initial E R diagram: 1 N M M Customer Supplier Book Available rom Purchases M From ound 1 Found On Holds Shelf 2010 John P. Shewchuk ISE 3024 Course Notes 9 – 7

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inal) E- diagram: firstName lastName title year price author publisher (Final) E R diagram: ame 1 N M M 0 ) Customer Book Available rom Purchases Supplier name address M bookId (0 .. 1) (0 .. M) (0 .. M) (2 .. N) (0 .. 60) From ound ISBN price saleDate rating state street ity tate zip 1 (1 .. 1) Found On Holds phone city state Shelf 2010 John P. Shewchuk ISE 3024 Course Notes 9 – 8 shelfId
et’s now check our conceptual schema for Anna’s

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3024-Chap9 - 9 CONCEPTUAL DATA MODELING ENTITY-RELATIONSHIP...

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