43 lines
1.9 KiB
Plaintext
43 lines
1.9 KiB
Plaintext
Primary key - It is the first key which is used to identify one and only one instance of an entity uniquely
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Candidate key - Key that consists of two or more attributes that uniquely identify any record on a table
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Foreign key - a primary key that i s used to connect two tables
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First normal form
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* contains only atomic values
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* atomic value is a value that cannot be divided
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* It states that an attribute of a table cannot hold multiple values. It must hold only single-valued attributes.
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Second normal form
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* It is in first normal form
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* All non-key attributes are fully functional dependent on the primary key
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* Non-key attributes are the attributes or fuelds of a table, other than candidate key attributes/fields on a table.
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* Composite key - a key of two or more attributes that uniquely identifies the row. (customer id and store id)
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* Non-key attribute is purchase location
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Third normal form
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* it is in second normal form
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* there is no transitive functional dependency
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* a is functionally dependent on b, and b is functionally dependent on c. in this case, c is transitively dependent on a via b
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* now all non-key attributes are fully functional dependent only on the primary key. in [table_book], both [gendre id] and [price] are only dependent on [book id]. in table [table_genre], [genre type] is only dependent on [genre id]
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================================================================================
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Hva er "Big data"
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Frank Danielsen
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================================================================================
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Hva er?
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Hva kan det brukes til?
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Hvordan brukes det i dag?
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+------------------------------------------------------------------------------+
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Store og komplekse dataset, som ikke er lett for mennesker å gå gjennom.
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Four V's
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Volume - The scale of the datas
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Variety -
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Velocity -
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Veracity - Uncertainty if data
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