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RE: PROV-ISSUE-4: agent subtypes?

From: Deus, Helena <helena.deus@deri.org>
Date: Thu, 14 Jul 2011 17:08:30 +0100
Message-ID: <316ADBDBFE4F4D4AA4FEEF7496ECAEF9062F95FD@EVS1.ac.nuigalway.ie>
To: "Luc Moreau" <L.Moreau@ecs.soton.ac.uk>, <public-prov-wg@w3.org>
Hi Luc,


I agree, agent subtypes are important. But are they not also domain dependent? 

Yes, in regard to your question – a catalyst, an enzyme are in fact agents.




From: public-prov-wg-request@w3.org [mailto:public-prov-wg-request@w3.org] On Behalf Of Luc Moreau
Sent: 14 July 2011 16:21
To: public-prov-wg@w3.org
Subject: PROV-ISSUE-4: agent subtypes?


Hi Reza,

Yes, it's a good idea to discuss agent subtypes as a separate thread.

>From my point of view, I want to be sure that we don't disallow some kind of agents, simply
because we had not thought about them. 

I believe that from a biology/chemistry point of view, a catalyst could be seen as an agent.

Views on this?


On 07/13/2011 07:41 PM, Reza B'Far wrote: 

Graham -

Thank you for your thorough response. Please note the following:

1.	I'm completely fine with sub-typing.  As long as the more concrete types (some more exact definitions of agent) are available, I'm fine with them "inheriting" from more generic types.  My chief concern as an implementer is to make sure that there is enough "typing" available so that there is no loss of data in the export/import process that can be avoided.  So, is the next step creation of a new email thread for sub-typing Agent?

On 7/12/11 11:48 PM, Graham Klyne wrote: 


I have two main responses to your comments: 

(1) your description of "Agent" here seems to me to be closer to what the provenance work has envisaged than that described in ws-arch document mentioned by Ryan. 

(2) I fully accept your need for volitional vs computational agent distinction for establishing certain kinds of trust in data.  But I still think that a generic agent class would keep things simpler for developers who are not so concerned with specific legislative or similar frameworks - I think it's easier to subclass a generic class as needed than to unite distinct classes. 

Given that yours is a concrete use-case addressing a real and immediate implementation need (I understand from comments by you and your colleague) I think it may be appropriate to include this person-vs-program distinction of agents in an initial model, but also providing a generic agent superclass for implementations that don't care or don't know what kind of agent is involved. 


Also, I note that even in my revised understanding per your comments, the provenance notion of "process execution" still isn't covered by the ws-arch terminology relating to agency. 


You mentioned PACE.  The matter of the relationship between work in provenance and work in trusted systems came up in the telecon to review work of the provenance incubator group, led by Yolanda Gil.  The point she made there was that [while these are clearly interconnected] the trust work has focused on trust in *systems*, where the provenance work is concerned with establishing credibility in specific datasets.  To this extent, I think we need to be cautious about over-extending the provenance model to also include concepts that would propoerly belong in a model for trusted systems. 


Reza B'Far wrote: 

   Folks - 

To add to Ryan's comments, I had put in a comment previously regarding using stronger types for agents.  From a practical implementation perspective, a subset of which Ryan mentions to be "audit" trail, etc., please note the following - 

   1. The distinction between the direct intervention of a human being 
      effecting the state of a data versus an indirect intervention is 
      absolutely crucial.  Without this, establishing "trust" (I mean 
      this from a formal perspective - something like PACE[1]) 
   2. I personally would lean towards one of the following options - 
          * Strong Typing of the Agent to multiple types and specifying 
            exactly what we mean by the types.  For example, /Human 
            Agent, System Agent/, etc.  I've mentioned this in a 
            previous thread.  Within all practical usages of provenance 
            that at least I'm concerned with, there are completely 
            different treatments of a "snapshot" (or whatever you want 
            to call it) of the state of an entity (which would be 
            considered something that is included in provenance) based 
            on whether or not there is direct human intervention (or 
            alternatively, far more specification and strong typing) of 
            the changes.  "Agent" is way to generic to be useful 
          * Reducing the use-cases of Agent to just User-Agent which is 
            the approach that is used in some of the other W3C standards 
            and is weaved into the fabric of www as we know today.  This 
            would reduce the scope of what an "Agent" is.  We may 
            possibly be able to leverage work of UAProf[2] and even if 
            not, we can learn from UAProf and CC/PP as examples. 
   3. The key of both (1) and (2) above is that we in order to have a 
      practical implementation, it is highly desirable to have some very 
      exact meaning for what "Agent" is, what it does, what the boundary 
      conditions are, etc.  I also highly encourage that we do NOT 
      include concepts that start going into RBAC and other security 
      related standards such as Role.  IMO, we need to reuse concepts 
      from these standards. 

I'm relatively new to the group, but have spent a lot of time reading the archives.  From an implementation perspective, I caution that if things are too generic and there is not enough specification (typing) and exactness in order to accommodate a larger tent, there may be long term implementation hurdles that are presented in terms of practical implementation.  In terms of a specific example, I think "Agent" above is one.  It's far too generically defined at this point, IMO. 

Please see references below. 

[1] - PACE - http://citeseerx.ist.psu.edu/viewdoc/summary?doi=, http://www.mendeley.com/research/architectural-support-trust-models-decentralized-applications/ 
[2] - UAProf - http://en.wikipedia.org/wiki/UAProf 
[3] - CC/PP - http://www.w3.org/Mobile/CCPP/ 

On 7/12/11 12:17 PM, Graham Klyne wrote: 


I think the important element that is missing is that provenance as understood so far by this group is intended to capture actual rather than potential or unrealized processes.  This is the idea that "Process execution" aims to capture.  The notion of "Agent" as described by the ws-arch spec is, to my mind, very much concerned with the potential rather than the realized computation. 

Although I'm not a long-time expert in this field, I think this is quite central to the notion of provenance we're trying to articulate and record, so it's an area where the terminology needs to be quite distinct from other usages.  You usage of "invocation" comes closer, I think, but I'm not convinced that yet another new term (it's not covered in ws-arch as I recall) is helpful at this stage. 

Because of the focus on actual computations, there's correspondingly less need (or so it seems so far based on the use-cases considered) to consider subteties of potential processes ("Recipes", "Roles", etc.).  I remain open on this, but I would avoid adding concepts for which there is not demonstrated need within the goals of provenance modelling and recording. 


Ryan Golden wrote: 

Thanks for taking a look at this, Graham, and I'd be interested to hear more feedback from others.  To address a couple of your comments: 

My intent with Agent was that it closely resemble the concept of Invocation, as you say.  I suppose the language "is a computational entity" does not effectively convey the intention.  I think Invocation necessarily implies an Invoker, so I chose a similar but broader concept of Realization.  How does does this strike you as a replacement for Process Execution? 

    An Agent realizes zero or more Roles on behalf of zero or more Persons or Organizations." 

My intention with Role is to broaden the idea of Recipe to include more abstract functions and purposes, but also to add a subtle implication (though not requirement) that it is something to be realized on behalf of a person or organization. 

In associating Person or Organization to the concepts of Agent and Role, the model comes closer to something that would be useful in representing audit trails or in establishing the trustworthiness of provenance assertions. 


On 7/12/2011 10:00 AM, Graham Klyne wrote: 

(ref. W3C Web Services Architecture Note <http://www.w3.org/TR/ws-arch> <http://www.w3.org/TR/ws-arch> ) 

Notwithstanding the slightly divergent usage in the provenance research community, I think there is value in using terms already adopted in the web services community where they align - I think that would help to make our outputs be more readily accepted, hence more relevant.  Thus, I think "Person or Organization" is reasonable term, replacing (as I understand) what provenance efforts have described as "Agent". 

But my understanding is that "Process execution" is *not* the same as ws-arch:"Agent", being intended to reflect a specific invocation of the programme or service.  I think the term ws-arch:"Agent" would more closely replace "Recipe". 

I'm not sure "Role" (ws-arch:"Service Role") has a direct correspondence in the terms we've discussed to date, though there is a notion of something like role in OPM.  Similarly for "Realizes" and "Acts on Behalf of". 


Ryan Golden wrote: 

   I'd like to bring a proposal up for discussion regarding Process Execution and its related concepts.  Although at the F2F1 there wasn't much discussion over "Process Execution," "Generates," "Uses," and "Agent," I believe more clarification and discussion is needed in these areas. 

High Level Proposal 
a) Rename the concept of "Process Execution" to "Agent," adjusting/adding a few properties 
b) Rename the concept of "Process/Recipe" to "Role," adjusting/adding a few properties 
c) Add the concept of "Person or Organization" 
d) Add the concept of "Realizes" 
e) Add the concept of "Acts on Behalf of" 

More Detailed Proposal 
a) Concept: Agent 
    - is a computational entity (narrowed from "piece of work") 
    - may use zero or more Entity States (Bobs) 
    - may generate zero or more Entity States  (Bobs) 
    - may realize zero or more Roles 
    - may have a duration 
    - may acts on behalf of a "Person or Organization" 
        Agent is a relatively well-defined industry term for an program acting on a user's behalf.   I propose it as a replacement for "Process Execution," which has the overloaded (and thus undesireable) term "process" in it, and does not necessarily imply that it is acting on behalf of any one person or organization.  In scenarios involving trust, audit, or change tracking, the ability to identify the "who" is crucial, and so the relation between Agent and Person or Organization is introduced.  "Person or Organization" is discussed further below.         Some other common variations are "software agent," or "user agent."  One notable difference between this concept and other agent concepts is that our Agent may have a duration.  I'm still undecided on the utility of the duration. 
        There will be some discussion here about non-computational agents.  I would question the utility of being able to assert relations involving Entity States (Bobs) and non-computational agents, and would ask you to first consider whether the same semantics could be better represented by a Role instead [see next]. 

b) Concept: Role 
    - is an abstract set of tasks which pertain to a job function 
    - may have semantics beyond the scope of the WG model (e.g., as described in the RBAC reference model) 
    - may be realized by zero or more Agents        Discussion: 
        Replaces the somewhat confused notions of "Agent" (as it was discussed at F2F1), "Process," and "Recipe".  Note that multiple Roles can be realized by a single Agent. 

c) Concept: Person or Organization 
    - is a real-world person or organization that an Agent acts on behalf of 

d) Concept: Realizes 
    [see Agent and Role] 

e) Concept: Acts on Behalf of 
    [see Agent and Person or Organization] 

I have adapted some of this proposal from concepts in the W3C Web Services Architecture Note <http://www.w3.org/TR/ws-arch> <http://www.w3.org/TR/ws-arch> , a document that I don't entirely agree with, but which has some useful models in it. I also referred to the NIST RBAC reference model. 





Professor Luc Moreau               
Electronics and Computer Science   tel:   +44 23 8059 4487         
University of Southampton          fax:   +44 23 8059 2865         
Southampton SO17 1BJ               email: l.moreau@ecs.soton.ac.uk  
United Kingdom                     http://www.ecs.soton.ac.uk/~lavm

Received on Thursday, 14 July 2011 16:09:04 UTC

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