Re: [Perl-workflow-devel] Using Workflow for managing home automation

[Sebastian S. <seb...@go...>]

Hello,

let me shortly follow up on my approaches until today.

After looking at the philosophy of petri-net approaches I decided for
myself that I currently am not convinced that this relates to my reality I
want to model. I sticked to the workflow approach. I did nit see hot the
producer/consumer approach of petri-nets can relate to my situation, where
I think i have only systems that have exactly one state at all times, if
they are correctly designd.

I inherited the workflow class and built around some functions I wanted to
have (just for the sake of experimentation, very dirty)

- path-finding capability (Dijkstra) used from the CPAN Graph module (I
iterate through all states/actions and create in parallel a graph object)
- in the context I foresee a field called "desired state" in which the user
can set the desired state of the system.
- I have states in the system which cannot be enforced by an action but can
only be reached through a null action in case a condition fails (in my
example: my PC is not ping-able any more). I skipped those transitions in
the graph so that they are not used for path finding (the system would be
stuck otherwise)
I use a little while loop to do the following:
- is the desired state equal to the current state? if yes - > i am happy.
if no:
  - check if there is a path through the graph from the current state to
the desired state. if no? damn! (should not happen by design of system). if
yes?
     - check if the next node on the found path is part of the currently
available actions. if yes?
        - do this action

until I am happy...

A test implementation with 8 different states now works...maybe I will find
out that I am on the wrong approach later when I design complexer systems
but for now...I am happy :)

Regards
Sebastian

2012/4/15 Alejandro Imass <ai...@p2...>

> On Sun, Apr 15, 2012 at 5:55 AM, Sebastian Stuecker
> <seb...@go...> wrote:
> > Hello folks,
> >
> > I hope it is ok to post to this list. If not, please tell me.
> >
> > I am trying to utilize the workflow framework that you guys have created
> and
> > I am fascinated about the possibilities and the way it is so generic and
> > configurable.
> >
> > However, there is one thing I am not sure if it is achievable. I have
> > defined a workflow with a bunch of states and I use this to control a
> > computer. This may sound weird. This "computer" can have several states:
> On,
> > Off, Booting, Halting, Unknown.
> >
> > Now, a user requests this computer to be just on. The user does not care
> > about the current state. The damn thing shall be on as quickly as
> possible.
> >
> > But if the computer is currently in the off state, it cannot be on
> directly
> > from there. It has to move through the booting-state and only if the
> booting
> > succeeds it will be on. I have actions defined how to move from off to
> > booting ( i just have a radio controlled socket to switch it on, but it
> > could also be wake on lan, etc.) and I have an action to move from
> booting
> > to on (some tests have to perform ok).
> >
> > I am looking for a way of "path-finding" from the actual state to a
> desired
> > state like I can do this for example with the Graph CPAN module which can
> > find the shortest path between two nodes.
> >
>
> Coming from the automation world I find your post quite interesting
> and in that sense the state-action-state paradigm is similar somewhat
> to ladder logic on a PLC. What I don't understand is this last bit...
> why do you need this path-finding stuff? As I see it, you should
> simply stick to the event-based (e.g. EDA, SEDA, EPC, etc.) model just
> like you would if you were automating using ladder language. Going on
> a limb, but IMHO I think you are confusing EPC-style workflows with
> Petri-net style WF engines.
>
> --
> Alejandro Imass
>
>
> > Is there any way to achieve this or do you think my whole idea is crap?
> :)
>