Databases Reference
In-Depth Information
Edm(e,d,m)
¬
Emp(e,d)
Ù
Mgr(d,m)
Work_age( Jack)
Works(e)
Emp(e,d)
Unemployed(e)
¬
¬
Work_age(e)
ÙØ
Works(e)
IC1(d,m1,m2)
¬
Mgr(d,m1)
Ù
Mgr(d,m2)
Ù
m1
¹
m2
IC2(e)
¬
Works(e)
ÙØ
Work_age(e)
The DB contains three base predicates: Emp, Mgr, and Work_age, stating
employees that work in departments, departments with their managers, and
persons who are of working age. It also contains three derived predicates:
Edm, which defines employees with the department for which they work
and the corresponding managers; Works, which defines persons who work as
those assigned to some department; and Unemployed, which defines persons
unemployed as those who are of working age but do not work. Finally, there
are two integrity constraints: IC1, which states that departments may
only have one manager, and IC2, which states that workers must be of
working age.
4.4.1
Change Computation
4.4.1.1 Definition of the Problem
A deductive DB can be updated through the application of a given transac-
tion, that is, a set of updates of base facts. Due to the presence of deductive
rules and integrity constraints, the application of a transaction may also
induce several changes on the intensional information, that is, on views and
integrity constraints. Given a transaction, change computation refers to the
process of computing the changes on the extension of the derived predicates
induced by changes on the base facts specified by that transaction.
Example 4.7
The content of the intensional information about Edm and Works in the DB
in Example 4.6 is the following.
Edm
Works
Employee
Department
Manager
Employee
John
Sales
Mary
John
Albert
Marketing
Anne
Albert
Peter
Marketing
Anne
Peter
