By Neeraj Sharma, Liviu Perniu, Raul F. Chong, Abhishek Iyer
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In our case, if the car is deleted the owner is deleted, too. 2. RESTRICT - the delete operation is “restricted” to the case where there are no such matching tuples (it is rejected otherwise). In our case, the car can be deleted only if it is not owned by a person. 3. NULLIFIES – the foreign key is set to null in all such matching cases and the tuple containing the primary key value is then deleted (of course, this case could not apply if the foreign key cannot accept null values). In our case, the car can be deleted after the IdentificationNumber attribute value of its former owner is set to null.
It was called data sublanguage ALPHA and it was never implemented in the original form. The language QUEL from INGRES is actually very similar to data sublanguage ALPHA. Codd also gave an algorithm, Codd’s reduction algorithm, by which Database Fundamentals 58 an arbitrary expression of the calculus can be reduced to a semantically equivalent expression of the algebra. 1 Tuple-oriented relational calculus A tuple variable is a variable that ranges over some relation. It is a variable whose only permitted values are tuples of that relation.
Every relation has at least one candidate key, because at least the combination of all of its attributes has the uniqueness property (the first property of a relation), but usually exist at least one other candidate key made of fewer attributes of the relation. 2 has only one candidate key K=(Type, Producer, Model, FabricationYear, Color, Fuel) considering that we can have multiple cars with the same characteristics in the relation. 3 by adding other two attributes like SerialNumber (engine serial number) and IdentificationNumber (car identification number) we will have 3 candidate keys for that relation.