Flashcards
Er models
Flashcards do conjunto (3)
- 1What are the categories of attribute types?- key attr. type
- simple (atomic) vs composite
- singe-valued vs multivalued
- derived - 2What is the key attr type used for?- Can be used to uniquely identify each entity
examples: product nr, SSN..
- Can also be a combination of attr. types. E.g flight Nr + departure date - 3What is the possible relationship between a weak entity and its owner?The relationship to the owner entity is called identifying relationship and it might only be 1:1 or 1:N. (A owner can have N "children", but a child cant have several parents)
In the latter case, the weak entity type needs partial key – an attribute which together with the owner’s key can identify the weak entity.
Informações
- Descrição
- Databas FlashCards sobre Er models, criado por Emma Tysk em 17-12-2017.
- Criado por
- Emma Tysk
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