Download Database Fundamentals- First editon by Neeraj Sharma, Liviu Perniu, Raul F. Chong, Abhishek Iyer PDF

By Neeraj Sharma, Liviu Perniu, Raul F. Chong, Abhishek Iyer

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A real-world data feature modeled in the database. B. A set of atomic values. C. A data characteristic. D. An ordered set of values that describe data characteristics. E. None of the above 7. Which of the following are relation properties? A. The primary key can’t have null values. B. There aren’t duplicate tuples in a relation. C. Attributes have atomic values. D. There are duplicate tuples in a relation. E. None of the above 8. A relation can have: A. A domain. B. An instance. C. A value. D. A degree.

By definition, every relation has at least one candidate key (the first property of a relation). In practice, most relations have multiple candidate keys. C. J. 2] gives the following definition for a candidate key: Let R be a relation with attributes A1, A2, …, An. The set of K=(Ai, Aj, …, Ak) of R is said to be a candidate key of R if and only if it satisfies the following two timeindependent properties:  Uniqueness At any given time, no two distinct tuples of R have the same value for Ai, the same value for Aj, …, and the same value for Ak.

They are the “glue” that holds the database together. Another way of saying this is that foreign-to-primary-key matches represent certain relationships between tuples. Note carefully, however, that not all such relationships are represented by foreign-to-primary-key matches. The DDL sublanguage usually has a FOREIGN KEY construct for defining the foreign keys. For each foreign key the corresponding primary key and its relation is also specified. 3 Relational data model constraints In a relational data model, data integrity can be achieved using integrity rules or constraints.

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