State diagrams use
I have encountered a less common use of state
diagrams. To me it looks at least strange. Here it
The system has the following behaviour:
1. The System needs to authorise every change that is
executed on a Business Entity A.
2. For create operations, user inspects the 'new'
value and authorises the creation.
3. For update operations,a user inspects the 'new'
value and the 'old' value and authorises the
4. For delete operations, a user looks at the 'old'
value and authorises the deletion.
So far so good. In order to describe the behaviour,
the modeller has attached the following states to A:
The states look fine to me, it's just the the modeller
wants to attached them only to only to 'old' instances
and not to 'new' instances. This looks odd to me, as
there could be stateless instances of class A.
It seems more natural to wrap the 'old' and the 'new'
values in a Change and associate the state to it. This
will make the description of pre and post conditions
more natural. For example, for creations
pre: old = null (undefined), new = X
post: old = X, new = X or null (undefined) if it's
removed from the system.
Looking forward to your comments.
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Received on Sun Apr 23 15:06:21 2006