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Entity Relationship Diagram

Based on the Information Engineering notation.

This is an extension to the existing Class Diagram. This extension adds:

• Additional relations for the Information Engineering notation.
• An entity alias that maps to the class diagram class.
• An additional visibility modifier * to identify mandatory attributes.

Otherwise, the syntax for drawing diagrams is the same as for class diagrams. All other features of class diagrams are also supported.

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Information Engineering Relations

Type	Symbol
Zero or One	|o--
Exactly One	||--
Zero or Many	}o--
One or Many	}|--

Examples:

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@startuml Entity01 }|..|| Entity02 Entity03 }o..o| Entity04 Entity05 ||--o{ Entity06 Entity07 |o--|| Entity08 @enduml

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Entities

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@startuml entity Entity01 { * identifying_attribute -- * mandatory_attribute optional_attribute } @enduml

Again, this is the normal class diagram syntax (aside from use of entity instead of class). Anything that you can do in a class diagram can be done here.

The * visibility modifier can be used to identify mandatory attributes. A space can be used after the modifier character to avoid conflicts with the creole bold:

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@startuml entity Entity01 { optional attribute **optional bold attribute** * **mandatory bold attribute** } @enduml

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Complete Example

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@startuml ' hide the spot ' hide circle ' avoid problems with angled crows feet skinparam linetype ortho entity "User" as e01 { *user_id : number <<generated>> -- *name : text description : text } entity "Card" as e02 { *card_id : number <<generated>> sync_enabled: boolean version: number last_sync_version: number -- *user_id : number <<FK>> other_details : text } entity "CardHistory" as e05 { *card_history_id : number <<generated>> version : number -- *card_id : number <<FK>> other_details : text } entity "CardsAccounts" as e04 { *id : number <<generated>> -- card_id : number <<FK>> account_id : number <<FK>> other_details : text } entity "Account" as e03 { *account_id : number <<generated>> -- user_id : number <<FK>> other_details : text } entity "Stream" as e06 { *id : number <<generated>> version: number searchingText: string -- owner_id : number <<FK>> follower_id : number <<FK>> card_id: number <<FK>> other_details : text } e01 }|..|| e02 e01 }|..|| e03 e02 }|..|| e05 e02 }|..|| e04 e03 }|..|| e04 e02 }|..|| e06 e03 }|..|| e06 @enduml

Currently the crows feet do not look very good when the relationship is drawn at an angle to the entity. This can be avoided by using the linetype ortho skinparam.