Relational Operation Abbreviation - Databases: design

Relational Operation Abbreviation

Operation Reduction is the one most often used in databases, making it possible to perform the restriction of a set of tuples in relations under certain conditions. Moreover, the conditions can be imposed both on one attitude and on the aggregate of relations. Thus, there are three options for using this operation:

• establishing a constraint through the relationship relationship;

• imposing a restriction on one relationship;

• imposing restrictions on related relationships, which is expressed in the sequential execution of the operations "Connection" and " and Abbreviation respectively.

A related relationship is a set of relationships in which there are one or more interacting attributes where it is possible to establish a logical constraint that causes a reduction in the set of tuples in both respects.

The action to establish relationships between relationships makes it possible to build a database structure that provides efficient data storage. Relationship relationships are performed based on the imposition of a logical condition (operations = & quot ;, & lt; & gt; & quot ;, & quot ;, , , etc.) on the attributes of both ratios, by which this relationship is established. For example, there are two relations "Student" and Exam (Table 1.7). In each of these relations there is an attribute "Name of the student", which allows you to organize the relationship between the relations.

Table 1.7

Student
No. Full name of the student
1 Karpetyan Arsen Gurenovich
2 Malyshkina Arina Ivanovna
3 Ivan Petrovich Polynov

Sample Source Relationships Student and Exam

Exam

Full name of the student

Score

Arsen Gurenovich Karapetyan

Great

Arina Ivanovna Malyshkina

Good

The

The

Doing the Cut in this example, it is advisable to execute by the condition = & quot ;, which will be expressed in such a logical expression - [Student's student] = [Student's Exam.] & quot ;. As a result of imposing this restriction, only such tuples of the initial relations that have the same student's name (Table 1.8) should be chosen. In this case, the resulting relation will contain in the header the attributes from both relations.

Table 1.8

Example of resulting relationship Exam table

To

Full name of the student

Score

1

Arsen Gurenovich Karapetyan

Great

2

Arina Ivanovna Malyshkina

Good

The

It is important that as a result of overlaying a logical expression, only the tuples that satisfy this expression fall into the resulting relation. A related constraint, as well as a single relation, may be subject to an additional constraint, which also performs the "Cut" operation. For this, the same logical operations are used as when binding relations. For example, if you impose a limitation on the resulting relationship from the example in question, that the "Estimate" = Excellent, the result will be as shown in Table. 1.9.

Table 1.9

Example of resulting relationship Exam table

with the superimposed additional condition

No.

Full name of the student

Score

1

Arsen Gurenovich Karapetyan

Great

The

The

A tuple where the score is Good under the specified condition is not selected and, accordingly, does not fall into the resulting ratio. Exactly the same operation can be performed on a single relation, restricting sets of possible tuples corresponding to a certain logical condition. And these conditions can be combined with the help of logical links And and OR & quot ;, and also the logical operation NOT & quot ;, which negates the corresponding logical action, can be superimposed on them.

thematic pictures

Also We Can Offer!

Other services that we offer

If you don’t see the necessary subject, paper type, or topic in our list of available services and examples, don’t worry! We have a number of other academic disciplines to suit the needs of anyone who visits this website looking for help.

How to ...

We made your life easier with putting together a big number of articles and guidelines on how to plan and write different types of assignments (Essay, Research Paper, Dissertation etc)