Introduction OOF                                                              

Short bases of visual dorp filtering (vdf)  are given, the way they derived and how they are to be applied in its projects.
The strength of OOF is particularly emphasized in the case of large number of table fields or the formation of complex questionnaires.

 Basic concepts of objectively oriented filtering              
Introduction                                                                                                       
It shows a problem of filtering and primary image of objects filtering.

Filter with one table field                                                                                  
In order to consider a problem we will look on a table that has a following  fields:  

                Table name : "order"

User would like to select all invoices with the dates larger than 25/05/1995.
He will write the following SQL equation:
            SELECT  *;
                        FROM order;
                        WHERE order_date > = 23/05/1995.
Simple and easy SQL equation. With * we marked all the fields from the table “order” that are included,
with required where equation.

Meanwhile, the user, from any reason conceives that he should modify filter equation.
For exempla, he wants to see all the numbers of invoices in some wanted date range (> = 23/05/1995, < = 28/06/1995).
Nothing easier, user will write new SQL equation:
            SELECT *;
                  FROM order;
                  WHERE (order_date>=23/05/1995 .AND. order_date <=28/06/1995)
or let’s write this equation on shorter way:
            SELECT  *;
                FROM order;
                       WHERE BETWEEN(order_date, 23/05/1995, 28/06/1995)

User had finished his job and he looked at required data with satisfaction. At the same moment, his chief came in the
office (oh, those chiefs, always have some requests) and he asked for reviews with new filter demand.
For exempla, all invoices <=15/06/1995.
            SELECT *;
                        FROM order;
                        WHERE order_date <=15/06/1995.