"Elwin Estle" <chrysalis_reb...@yahoo.com> wrote
The class in question, does, in fact, deal with a thing.
The problem is, the "thing" is highly mutable.
You can mutate objects, that is not a problem.
But you need to be sure you need to.
Is this really a series of different types of casting or
a single Workpiece going through a sequence of Actions
each Action having a set of quality data associated?
If so it may be that you have a single Workpiece class
and a relatively small heirarchy of Actions.
A raw casting comes into a factory. It is listed as such.
When machined, this part number changes to a
different part number. The raw casting has no
"quality related" stuff, but the machined casting does,
Is it the casting or the machining that has the quality
related data? ie Is it casting specific or operation specific?
...because, the raw casting may go through multiple
operations to get to it's final state.
Do you know in advance what these operations will be?
Can you assign a WorkPlan to the Workpiece? Each
step of the plan having an associated Action?
Each of those operations on separate machines will
have a different set of quality checks associated with it.
So here we clearly say it is the Action that has the
data associated...
...or it might be a part that goes from a raw casting to
a sort of "mini-assembly" such as a rocker lever ...
but it is still the same thing, and each one of those
steps may have some sort of quality check involved.
So a workpice can consist of other WorkPieces.
And again tyhe Actions associated have quality data
Lets complicate things even further. One raw casting
may be machined into multiple part numbers.
Is that true? Or is it one type of casting?
Each instance of casting will surely onmly go through
one specific set of actions? If we treat them all as generic
workpieces then the Actions are different but the workpiece
concept remains constant?
Or, are we saying that a single original workpiece can
be cut into several distinct workpieces? Again thats
not necessarily a problem, objects can clone themselves
and have the clones diverge thereafter.
Perhaps the only thing that changes is the location
of a single hole. But again, each one of those part
numbers may go through multiple machining operations
on different machines, with different quality checks.
This is done through something called a "tabbed"
blueprint, wherein there is a master number, but there
are "tabs" indicating that if you changes such and
such feature, then the part number isn't the master
number, but the tabbed number.
I'm not sure I follow that bit.
So, in essence, there's a sort of "network" of "is-a"
and "has-a" information.
I see a lot of "has-a" but very little "is-a" at this stage.
In fact I don't see any "is-a" yet, althopugh I can see
where some might emerge in the future.
have a sort of "component aggregate" class, which
would cover not only single parts, but assemblies
I think that will be essential.
if a part was as simple as a raw casting that is
just machined into a finished part and that's it,
it would still be treated as a sort of assembly,
One of the key features of assemblies is that they
should scale down to a single item just as easily
as up to many parts.
So there's all this information associated with a
given part. I am thinking it has a sort of tree structure.
I think there probably is and you should look into
the composite pattern to build that.
I am just wondering if some of the branches of
the tree should be separate classes
Probably, but not so many different classes as
you currently suspect.
...and yeah, I know, it's kind of a complex problem
for a newbie to be thinking about.
Yes, very challenging. This is one of the kinds of
problem where the best solution is probably not be
the first one you think of. But you won't know that
till after you try building it!
My proposal is only a guess based on a quick
review of your description and no local domain
knowledge...
You may also find it useful to think through the
state model for your castings/workpieces. That
may help to constrain the number of Actions/operations
required.
--
Alan Gauld
Author of the Learn to Program web site
http://www.alan-g.me.uk/
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