Karteikarten
SCC 201 - Second Normal Form
Karten in diesem Stapel (13)
- 1Why is deletion dependency a problem?We could delete an only record
This means we lose the local information( we might want to contact them at a later date) - 2Problem with update dependencies?if we need to update a specific attribute, we must update all occurrences to maintain consistency.
- 3When can a relational schema be in second normal form?– it is in first normal form, and
– every non-prime attribute A in R is
fully functionally dependent on the primary key of R or
– every non-prime attribute A in R is not partially dependent on any key of R - 4What is a prime attribute?Prime attributes are the attributes of the candidate key which defines the uniquenes
- 5What is a non-prime attribute?an attribute that does not occur in ANY candidate key is called a non-prime attribute.
- 6What is functional dependency?Functional dependency is a relationship that exists when one attribute uniquely determines another attribute. If R is a relation with attributes X and Y, a functional dependency between the attributes is represented as X->Y, which specifies Y is functionally dependent on X.
- 7When can an attribute be called non -prime• An attribute is called nonprime
– If it is not a prime attribute – that is,
if it is not a member of any candidate key - 8An attribute of relation schema R is called a prime attribute of R if it does what?• An attribute of relation schema R is called a prime attribute of R
– If it is a member of some candidate key of R - 9What is a function?– A function is an operation
• taking a set of arguments, and
• returning a single result - 10State a formal definition of functional dependency?– Attribute B of relation R is functionally dependent on attribute A of R if, at every instant of time, each value in A has no more than one value in B associated with it under R.
– This is written as A right arrow B - 11If Catalogue (Stock) right arrow Catalogue (Supplier, part#), we can also say that?(Supplier, Part#)
determines value of (Stock)
(Supplier, Part#) is
determinant of (Stock) - 12What is full functional dependency?– Full dependency occurs when set of attributes E is functionally dependent on the whole of set D, but not on any subset of D
- 13Why does 2nd normal formal enable better organisation?-It saves space
-updating in consistent manner is far easier
-we have avoided deletion dependency
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- Karteikarten am SCC 201 - Second Normal Form, erstellt von Ayo Olutobi am 29/03/2017.
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- Ayo Olutobi
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