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Distributed Database Systems
Example 11.14
Let us consider the following join operation that involves three different relations Student, Course,
and Teacher, and over the attribute course-id.
Student
Ԯ
course-id
Course
Ԯ
course-id
Teacher
Further assume that the relations Student, Course and Teacher are stored at site 1, site 2 and site 3
respectively. The corresponding join graph is depicted in fi gure 11.14.
Fig. 11.14 Join Graph for a Distributed Query
Student
Course
Teacher
course-idcourse-id
Site2
Site3
Site1
There are various ways to perform the above join operation, but to select the best one, some
more information must be known: size(Student), ...