Sequence Calls

Note
This topic applies only to SWCs specified as block diagrams.

A sequence call is linked to every assignment operation or every method call of an included component. Every sequence call represents an instruction in an ASCET diagram. Sequence calls determine the control flow in diagrams by assigning every instruction to a method or runnable, and determining the order of the instructions within a method or runnable.

In the software component editor, connecting lines between elements and/or operators are shown as colored lines as long as the sequencing for the instruction or operation linked to the element has not been resolved. The color indicates that the sequencing still has to be resolved. All lines to which a sequence call has been assigned are shown in black.

You can edit the sequence calls individually or in groups, manually or automatically.

Connectors are used to connect an assignment with a control flow instruction such as If Then or If Then Else.

Editing Individual Sequence Calls

Individual sequence calls can be assigned automatically or edited in the sequence editor. In the sequence editor, you can either enter a sequence number, or use a button to assign the next free number.

Automatic assignment, as well as the Next free button in the sequence editor, use a set of rulesto determine the sequence number.

Editing Several Sequence Calls

A large number of sequence calls may be necessary in complex diagrams. In that case, the possibilities to edit sequence calls in groups can be helpful. You can edit all sequence calls in a selected part of the diagram, all sequence calls assigned to a selected method/runnable, or all sequence calls in a complete diagram.

The sequencing algorithm uses a logical model graph that is computed from the inputs and outputs of all graphical elements. The algorithm tries to find dependencies between the graphical elements, but severe restrictions apply.

independent subgraphs

One diagram can have several independent subgraphs. The order the sequencing algorithm assigns to the independent subgraphs cannot be predicted.

EXAMPLE
The sequencing algorithm will notice that the addition d = a + c has to be computed last because it depends on the results of the additions a = b + 1 and c = b + 2. Therefore, the addition d = a + c will be assigned the highest sequence number. However, the algorithm cannot decide whether a or c needs to be computed first. The lowest sequence number is assigned arbitrarily either to a = b + 1 or to c = b + 2.

EXAMPLE

control flow elements
If the branch of a control flow element is connected to more than one action, the sequencing algorithm cannot decide which action has to be computed first. The sequence numbers of the connectors are assigned arbitrarily.
EXAMPLE
If statement
Even though the lower action on the Then branch, b = b + a, depends on the upper action a = 1.0, the sequencing algorithm may assign the lower sequence number to b = b + a.

EXAMPLE
If statement Even though the lower action on the Then branch, b = b + a, depends on the upper action a = 1.0, the sequencing algorithm may assign the lower sequence number to b = b + a.

several methods/processes

One diagram can contain several methods or runnables. Elements that belong to a method or runnable (i.e. arguments, return values, method-/runnable-local variables) can be used only in that particular method or runnable, but all other elements can be computed in any method or runnable. For these elements, the sequencing algorithm tries to determine a method/runnable by checking whether the inputs/outputs of a computation chain belong to a particular method/runnable. If that check fails, any method/runnable can be used.

EXAMPLE
Assume a class with three methods (compute, reset, out): Sequence call A can only be assigned to the reset method because the initValue argument is not available in the other methods. If another method is selected for sequencing, this sequence call remains empty. Sequence call B can only be assigned to the out method. If another method is selected for sequencing, this sequence call remains empty. Sequence call C can only be assigned to the compute method. If another method is selected for sequencing, this sequence call remains empty. Sequence call D can only be assigned to the compute method because the local variable locvar argument is not available in the other methods. If another method is selected for sequencing, this sequence call remains empty. Sequence call E does not belong to a particular method. It will be assigned to whichever method is selected for sequencing.

EXAMPLE