RE: TOSCA workflows

Thanks Philippe. This approach could have value for Version 1.3, but would no longer work for Version 2.0 where TOSCA no longer defines any normative types. Because of this:

The Version 2.0 language can no longer define any normative states
In fact, the idea that there is a single state associated with a node does not work when you define multiple interfaces on that node. The state machine associated with each interface should be treated separately.

To deal with these issues, we have explored the following:

Associated a separate âstateâ attribute with each interface
For the operations of an interface, define âpreconditionsâ that list the valid states in which the operation can be called, and âpostconditionsâ that define the state into which the interface transitions when the operation succeeds.

What needs to be investigated further is how interface operations on relationships interweave with interface operations on nodes. We need language support for defining this as well.

Thanks,

Chris

From: Philippe Merle <philippe.merle@univ-lille.fr>
Sent: Monday, February 28, 2022 12:35 PM
To: Chris Lauwers <lauwers@ubicity.com>
Cc: tosca-comment <tosca-comment@lists.oasis-open.org>
Subject: Re: TOSCA workflows

Hi Chris,

> I'm curious about your use case for imperative workflows.

We are developing a tool to verify imperative workflows and detect behavioural bugs, e.g.

  workflows:
   deploy:
   steps:
   deploy_x:
   target: x
   activities:
   - set_state: creating
   - call_operation: Standard.create
   - set_state: starting
   - call_operation: Standard.start

This previous sequence of activities could be considered as incorrect as some activities are missing, i.e.: set_state: created and set_state: started

   activities:
   - set_state: creating
   - call_operation: Standard.create
   - set_state: created # missing
   - set_state: starting
   - call_operation: Standard.start
   - set_state: started # missing

To validate this tool, we are currently generating both correct and incorrect imperative workflows automatically.

But to go a step beyond, we are searching concrete imperative workflows.

> We have had discussions about removing support for imperative workflows from the language and

This will be a big feature removal!

But the removal could be justify if no TOSCA orchestrator implements imperative workflows.

> generalizing support for declarative ("automatically generated") workflows.

We are developing a generator to automatically generate imperative workflows from a topology template.

> We have also looked at supporting a more general "state/event" model where topology-wide behavior "emerges" as a result of state/event transition tables defined locally on each node and/or relationship.

In our approach, we are defining a finite state machine where transitions are labelled by workflow activities (e.g. set_state: created, call_operation: Standard.create).

A+

Philippe Merle

De: "Chris Lauwers" <lauwers@ubicity.com>
Ã: "Philippe Merle" <philippe.merle@univ-lille.fr>, "tosca-comment" <[email protected]>
EnvoyÃ: Lundi 28 FÃvrier 2022 20:54:20
Objet: RE: TOSCA workflows

Hi Philippe,

I'm curious about your use case for imperative workflows. We have had discussions about removing support for imperative workflows from the language and generalizing support for declarative ("automatically generated") workflows. We have also looked at supporting a more general "state/event" model where topology-wide behavior "emerges" as a result of state/event transition tables defined locally on each node and/or relationship.

Thanks,

Chris

-----Original Message-----
From: tosca-comment@lists.oasis-open.org <tosca-comment@lists.oasis-open.org> On Behalf Of Philippe Merle
Sent: Sunday, February 13, 2022 6:39 AM
To: tosca-comment@lists.oasis-open.org
Subject: [tosca-comment] TOSCA workflows

Hello,

I am conducting a research work around TOSCA imperative workflows.
Could one point me to freely available TOSCA imperative workflow examples?
Which TOSCA orchestrators could execute TOSCA imperative workflows?

Thank you in advance for your replies.
Philippe Merle
Inria researcher

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