Boolean Expressions and Fielded Buffers

The next action taken by an application program is frequently determined by the value of one or more fields in a fielded buffer received (by the application) from another source, such as a user's terminal or a database record. FML provides several functions that create boolean expressions on fielded buffers or VIEWs and determine whether a given buffer or VIEW meets the criteria specified by the expression.

Once you create a Boolean expression, it is compiled into an evaluation tree. The evaluation tree is then used to determine whether a fielded buffer or VIEW matches the specified Boolean conditions.

For instance, a program may read a data record into a fielded buffer (Buffer A), and apply a Boolean expression to the buffer. If Buffer A meets the conditions specified by the Boolean expression, then an FML function is used to update another buffer, Buffer B, with data from Buffer A.