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Chapter 6: Problem 9

How does tuple relational calculus differ from domain relational calculus?

Short Answer

Expert verified
Tuple relational calculus uses a variable to represent an entire tuple whereas domain relational calculus pertains to a single attribute. Also, tuple relational calculus is preferred when a query refers to an undefined number of attributes, but domain relational calculus is used when a query has a specified, fixed number of attributes.

Step by step solution

01

Defining Tuple Relational Calculus

Tuple relational calculus is a non-procedural query language which specifies to select the tuples in a relation. The main focus is on 'what to retrieve' rather than 'how to retrieve'.
02

Defining Domain Relational Calculus

Domain relational calculus is also a non-procedural query language, but it uses the list of attribute to be selected from the relation based on the condition. The key here is that domain relational calculus does not use variables.
03

Identifying the differences

In tuple relational calculus, a variable represents an entire tuple or record, whereas in domain relational calculus, a variable represents only a single attribute. Secondly, tuple relational calculus is used when a query refers to an undefined number of attributes while domain relational calculus is used when a query has a fixed number of attributes.

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Most popular questions from this chapter

When is a query language called relationally complete?

Show how you may specify the following relational algebra operations in both tuple and domain relational calculus. a. \( \sigma_{A=C}(R(A, B, C))\) b. \(\pi_{}(R(A, B, C))\) c. \(R(A, B, C) * S(C, D, E)\) d. \(R(A, B, C) \cup S(A, B, C)\) e. \(R(A, B, C) \cap S(A, B, C)\) \(f(A, B, C)-S(A, B, C)\) g. \(R(A, B, C) \times S(D, E, F)\) h. \(R(A, B) \div S(A)\)

What role does the concept of foreign key play when specifying the most common types of meaningful join operations?

Consider this query: Retrieve the ssns of employees who work on at least those projects on which the employee with \(\operatorname{ss} N=123456789\) works. This may be stated \(\operatorname{as}(\text { FORALL } x)(\text { IF } P \text { THEN } Q),\) where \(\bullet\) \(x\) is a tuple variable that ranges over the PROJECT relation. \(\bullet\) \(P \equiv\) employee with \(\operatorname{ssN}=123456789\) works on project \(x\) \(\bullet\) \(Q \equiv\) employee e works on project \(x\) Express the query in tuple relational calculus, using the rules \(\bullet\) \((\forall x)(P(x)) \equiv \operatorname{NOT}(\exists x)(\operatorname{NOT}(P(x)))\) \(\bullet\) (IF \(P \text { THEN } Q) \equiv(\mathrm{NOT}(P) \text { OR } Q)\)

What is the FUNCTION operation? What is it used for?
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