23493189
Description
Flashcards by Sophia Lynch, updated more than 1 year ago
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Created by Sophia Lynch
almost 4 years ago
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| Question | Answer |
| 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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