The selection condition for a view is produced by logically linking simple selection conditions. The type of logical connection involved is determined in the AND/OR field. Each of the simple selection conditions linked in this way is either an elementary selection condition or the negation of an elementary selection condition. The NOT field determines which of these two alternatives applies. An elementary selection condition is produced by comparing a field from one of the source tables of the view with a comparison value. The compare operator used is specified in the field "Op".
A check is made of the selection condition of the view to be activated to see whether it satisfies the following requirements: a) The NOT field of each simple selection condition contains either ' ' (for no negation) or 'NOT' (for negation). b) The AND/OR fields contain only the three allowed values 'AND' (logical AND), 'OR' (logical OR), and ' '. ' ' never occurs between two simple selection conditions. c) Two simple selection conditions linked by OR refer to the same field from the same source table. d) The field "Op" contains one of the following compare operators: 'EQ' = 'equal' 'NE' = 'not equal' 'GE' = 'greater than or equal to' 'GT' = 'greater than' 'LE' = 'less than or equal to' 'LT' = 'less than' 'LK' = 'like screen'