Materialization of Views

ConceptBase offers support for maintaining externally materialized views incrementally, but there is currently no automatic support for materialization of views without ECArules. Materialization of views means, that deduced information is stored in the object base. We provide here an example, how to materialize and maintain simple views.

Class Employee with 
attribute
    salary : Integer
end

View EmployeeWithHighSalary isA Employee with
constraint
    c : $ exists i/Integer (this salary i) and (i > 100000) $
end

Class EmployeeWithHighSalary_Materialized 
end

The view EmployeeWithHighSalary contains all employees who earn more than 100.000. The class EmployeeWithHighSalary_Materialized will contain the same employees. This implemented by the following ECArules:

ECArule EmployeeWithHighSalary_Materialized_Ins with
ecarule
    er : $ x/Employee
    ON Tell(In(x,Employee))
    IF new(In(x,EmployeeWithHighSalary))
    DO Tell(In(x,EmployeeWithHighSalary_Materialized)) $
end

ECArule EmployeeWithHighSalary_Materialized_Del with
ecarule
    er : $ x/Employee
    ON Untell(In(x,Employee))
    IF In(x,EmployeeWithHighSalary)
    DO Untell(In(x,EmployeeWithHighSalary_Materialized)) $
end

ECArule EmployeeWithHighSalary_Materialized_Ins_salary with
ecarule
    er : $ x/Employee y/Integer
    ON Tell(A(x,salary,y))
    IF new(In(x,EmployeeWithHighSalary))
    DO Tell(In(x,EmployeeWithHighSalary_Materialized)) $
end

ECArule EmployeeWithHighSalary_Materialized_Del_salary with
ecarule
    er : $ x/Employee y/Integer
    ON Untell(A(x,salary,y))
    IF In(x,EmployeeWithHighSalary)
    DO Untell(In(x,EmployeeWithHighSalary_Materialized)) $
end

The first rule checks, if the employee belongs to the view, when the employee was inserted. Note, that we don't use the constraint of the view in the ECArules, we just reuse the view definition here. The second rule does the same for deletion of employees.

The third rule checks, if the employee is an instance of the view class, when the attribute salary was inserted. Again, the fourth rule does the same for deletion of the attribute.

If the number of employees is large it is more efficient to ask for the instances of materialized than to evaluate the view. However, if updates occur quite often, materialization is not good, because materialized view must be maintained for every update transaction.