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Sequences not State Machines

20120610 (2012 June 10 Sunday)

Introduction

There are some sequences in the xyz product UI, used for setup (wizards) that are modeled as state machines they would be simpler if modeled as sequences as shown below.

Properties

The Sequences have the following properties:

  • The sequence can be traversed forwards and backwards.
  • The Sequence when traversed backwards follow the same path as when traversed forwards.
  • Some steps can be skipped, if setting from other steps disable them.
  • A step can only disable a later step.

Definition

Each Step has a boolean expression as its entry condition. If the expression evaluates to true the step is performed, if it evaluates to false the step is skipped. The input values to the boolean expressions are set in other steps. Steps are ordered, just a simple sequence. If you skip a step you move to the next(prev) and decide whether to skip that etc. until you find one that has a true entry condition or you get to the end of the list.

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