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14 Cards in this Set
- Front
- Back
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What is an Entity |
Building blocks of an ERD they are shown as a table. They represent people, places objects, things, events, or concepts about which data is being collected. Nouns. General representation of all entity instances. |
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What is a Entity-Relationship Model |
A visual representation (picture) of entities, their attributes, and the relationships between entities. |
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Attribute |
Property or characteristics of entities or relationships. Do not use the space character, instead use the underscore character. Shown as a column on an ERD table. |
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Relationship |
business rules governing associations. Verbs that link entities. Represented by a diamond on ERD. can have attributes (intersection Data). |
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Entity instance |
a single example of an entity |
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Primary key |
One or more attribute that uniquely identifies each instance of an entity (represented by an asterisk). |
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Unary relationship |
Recursive relationship between instances of the same entity. |
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Binary relationship |
relationship between two entities. |
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Ternary relationship |
relationship between three entities |
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Cardinality |
how many instances of one entity are associated with an instance of the other entity. Outer symbol (the one closer to an entity). |
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Modality |
Minimum requirements either mandatory (vertical dash) or optional (oval). Inner symbol. |
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crows feet |
many relationship |
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single vertical line |
single relationship |
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Associative entity |
When there is a many-to-many relationship there is always an intersection entity. (table between to tables) |
