Customized Look-Up Table

I am a newbie AXAPTA developer. I want to solve the following situation, I have a form in which I have a grid. I am interested in 2 fields in a row of the grid. Name of these fields are Category and TypeId. These two fields have arrows on right (lookup arrows). I want to customize the look up table of Category field according to the chosen text in the look up table of TypeID. The lookup table of Category field shows the table “A”, which has Category and Type columns. This look up table is implemented in another form with respect to the form of the grid. The lookup table of TypeId shows the table “B”, which has the columns TypeId and CategoryType. Then I want to do the following in the grid. Look to the TypeId field in the grid, take its value and find the corresponding CategoryType in the table “B”, and then show those Categories in table “A” in the Category field of the grid which has the same Type as in the Category Type of the “B”. Eg: Table A Category Type A B X B Y C Table B TypeId CategoryType 1 B 2 C 3 B Then if the TypeId field in the grid is 1, then I will show A and X in the lookup table of Category field. Can I achieve this with some relations on tables? Or what do you suggest? (Tables contains more columns, I omitted them for simplicity)

Try to modify the ‘lookup’ method on the field (in the form). Example: the ActivityId field on the overview grid in the ‘ProjJournalTransEmpl’ form.