Data Modelling (ERD)

Beschreibung

BSNS115
Sophia Lynch
Karteikarten von Sophia Lynch, aktualisiert more than 1 year ago
Sophia Lynch
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Zusammenfassung der Ressource

Frage Antworten
What is an 'Entity Relationship Diagram (ERD)'? An abstract diagram (a plan) that models the nature of the information to be recorded in the business.
Do computers or humans use ERD? It is used by people (analysts) to capture requirements and inform the design of databases. Not directly used by computers.
What does ERD stand for? Entity-relationship Diagram.
What is this pointing to? The ENTITY.
What is this pointing to? The ATTRIBUTES.
What is this pointing to? The UNIQUE IDENTIFIER.
What is this pointing to? The RELATIONSHIP.
What three things indicate that something is an entity? 1. Is it a SPECIFIC thing we need to know about? 2. Is it RELEVANT to the problem? 3. Do you need to deal with MORE THAN ONE occurrence?
What is the difference between entity type and entity instance? Entity Instance = A physical manifestation of an entity. Entity Type = Describes common nature of entity - what you see in ERD.
What is an attribute? An individual property of an entity type. May be used to link entity instances.
What is a relationship? Reflects a real-world association between entities. (E.g. a sale is made to many entities)
What is 'Relationship Cardinality'? Denotes "how many" instances of entity A are related to instances of entity B, vice versa.
What cardinality is this? 1 : 1 (One-to-one) 1 entity instance to another. (Not common)
What cardinality is this? 1 : M (One-to-many) 1 entity instance to many. (Most common)
What cardinality is this? M : N (Many-to-many) Many entity instances to many entity instances. (Fairly common)
What is the difference between cardinality symbols and participation symbols? Cardinality = closest symbol to the entity box. Participation = innermost symbol.
What does this sign mean? Optional. "0"
What does this sign mean? Mandatory. " I "
What does this sign mean? One (and only one)
What does this sign mean? Zero or one.
What does this sign mean? One or many.
What does this sign mean? Zero or many.
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