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14 Cards in this Set
- Front
- Back
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primary key
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a field which uniquely identifies a record in a relational database
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compound key
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a primary key made up of more than one field due to the unsuitability of a single field as a primary key
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surrogate key
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a primary key which is made up when there is no suitable primary key or compound key...see above
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foreign key
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a foreign key is a primary key in another table which is used for linking purposes in a reltional database
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entity integrity
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every relation must have an primary key and it must be unique and not null
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referential integrity
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foreign keys must have two states, either it should be linked to a primary key of a related relation or in special circumstances it should be a null value
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rows
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each row in a relation must be unique, this means that the combinations of values in the columns cannot be the same
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Data Dictionary
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A data dictionary is a form of metadata as it gives information about the domain constraints which apply to each attribute in an entity.
It is essentialy creating a design for the various database tables which will be created in the relational database management system |
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Information contained in a data dictionary/columns....Entity set
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the name of the entity set, when the database is created this is the name of the table
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Name
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this is where the names of the attributes are listed
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Type
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this refers to whether the data is an integer or text etc
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Size
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this is a constraint placed on data of type text which constrains there maximum length. this helps make the database more efficient as it only takes up the required amount of space
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Validation
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this is the range of accepted values for each attribute. The validations availible is a presence check, null values are not allowed. range check, value entered must be above/below certain values. format check, the data entered must conform to a specific pattern and/or number of characters. permitted value, only one of a selection of values is allowed
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Index/key
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This is where foregin keys and primarys keys are idefntified.
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