Re: [soa-rm-ra] multiple descriptions [was: [soa-rm-ra] Questions on action model]

Frank,

The assumption is that most of the nuts & bolts description, e.g. WSDL, comes from the service provider.  If *Mart twists the provider's arm to do things a certain way, that may be irrelevant to other consumers who are only interested in using what is there, not where there came from.  [Parse that carefully ;-) ]

As for consumer input, that is why I included Annotations.

As for Authoritative, that is why the model for associating description values has a spot for who authored the value.  Given that information, it is up to the consumer to decide what is authoritative.

Ken

On Oct 16, 2007, at 12:08 PM, Francis McCabe wrote:

Ken & Michael

 Is a description of a service that was *not* originated by the *owner* of the service not still a description of the service?

 This might be thought of as a corner case, but in fact is far from that. It is not always the case that the owner of a service is the stronger partner: the consumer may be; the classic example of which is *Mart where the buyer in the supply chain dictates: you *shall* offer a service whose description is ...

 Similarly, the manageability description of a service may have nothing to say to consumers of the service; but is also a description of the service.

 Once you open your mind, it is easy to see lots of potential examples here.

 On the other hand, it may be a good idea to borrow from DNS the idea of the *authoritative* description; but that authority would have to be qualified: "this description is authoritative for the purposes of using a service" (or whatever)

Frank

On Oct 16, 2007, at 8:27 AM, Ken Laskey wrote:

 
Michael,

I see your discomfort and if all we had were multiple, independently generated descriptions, this would certainly lead to ambiguity and contradiction.

I have often talked about a service description as being a table of contents, so less than the source of many description elements, it is the collection points of things created for other, related purposes.  For example, I do not see writing policies into each service description but I see those with expertise in rules systems developing policies in parallel and the service description author would link to the existing policies.  In the same way, I do not see duplicating my address and phone number for every service for which I am a responsible party, but I do see a link to the resource where my contact (and possibly other personal information) is maintained.

In this way, a different subset of possible description could be emphasized for different contexts, but the subsets would leverage common resources for the description elements.

At one time, I advocated the idea of a "complete description" where the description would explicitly collect the description elements needed for the context but would provide other links where additional description sets or description elements could be found.  The idea was a given description would highlight what was needed for the context but there would be tendrils to the rest of the world where more information resides.

Ken

On Oct 15, 2007, at 4:43 AM, Poulin, Michael wrote:

 
Duane wrote:  "In an ecosystem of services, there could potentially be many service descriptions for a service.  The service description a consumer uses may be dependent on the entity the consumer interacts with when they use the service, or it could be dependent on the particular context the service description is provided.  Because of unforeseen possibilities for a service to have multiple service descriptions, I do not think the OASIS SOA RA can qualify one service to one service description."

I have a lot of concerns about underlined statements.

1) Service description gets used as the service definition now. I agree that in an ecosystem not all information about the service is in the Service Descriptor. However, in this case, I prefer to recognise that I have different 'domains' in the ecosystem of services (voice, signs, UDDI, etc.) where the Service Description is the single unique one.

2) To me,  the "service description a consumer uses may be dependent on the entity the consumer interacts with when they use the service" looks much more like an execution context and related Service Contract than a service description. Again, "be dependent on the particular context the service description is provided" is either services ecosystem domain specific Description or the EC and Service Contract.

3) as I mentioned before, SOA RM states that EC is not a context of service interaction only ( though in many places it says so ) but also the context of service execution per se. If we allow "a service to have multiple service descriptions" (w/o defining concrete conditions where it is possible), we have to clearly distinguish it from a service to have multiple service descriptions in multiple service execution contexts - interaction and execution ones.

4) I, personally, dislike the idea of "a service to have multiple service descriptions", at least, in the same Service Description Repository. Though this is a lower level technical implementation detail,  it is VERY important for practical use of SOA and quoted statement above can easily screw it, which I hate.

- Michael

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From: Duane Nickull [mailto:]

Sent: 12 October 2007 16:49

To: Ken Laskey; Scott Came

Cc: 

Subject: Re: [soa-rm-ra] Questions on action model

Concur.  Look at the cardinality of WSDL. Not everything is mandatory either.  On a purely logical level, consumers can use only that which they require.  It is unlikley that any one service description artifact would in fact contain *all* the information required.

At least some info is known via alternative mechanisms (voice, signs, UDDI, etc.)

Duane

On 10/11/07 6:22 PM, "Ken Laskey" <> wrote:

The RM says

The service description represents the information needed in order to use a service. In most cases, there is no one “right” description but rather the elements of description required depend on the context and the needs of the parties using the associated entity.

Thus, the implication is there may be overlapping descriptions relevant to different contexts.

Ken

On Oct 11, 2007, at 8:08 PM, Scott Came wrote:

Danny:

I don't personally have a strong feeling one way or the other on this

issue.  I did sense the "one description" position as the subcommittee

consensus, however...mostly from reading the RA 0.2 draft.

Thanks.

--Scott

-----Original Message-----

From: Danny Thornton [mailto:]

Sent: Thursday, October 11, 2007 3:55 PM

To: Scott Came; 

Subject: RE: [soa-rm-ra] Questions on action model

Scott,

Thank you for the summarization.  The only statement I

have an exception with is 3, A service has one

description.

In an ecosystem of services, there could potentially

be many service descriptions for a service.  The

service description a consumer uses may be dependent

on the entity the consumer interacts with when they

use the service, or it could be dependent on the

particular context the service description is

provided.  Because of unforeseen possibilities for a

service to have multiple service descriptions, I do

not think the OASIS SOA RA can qualify one service to

one service description.

Danny

--- Scott Came <> wrote:

Subcommittee:

I'd like to take attempt a summarization of this

thread.  Note the word

"attempt"...please let me know if I've misconstrued

anything said so

far.

1. The action model of a service may contain

multiple actions

2. The actions in a given service's action model may

produce

distinct real-world effects, meaning that a consumer

may choose to

interact with (invoke?) some subset of actions and

not others

3. A service has one description, but that one

description may make

specific reference to particular actions in order to

describe their

individual effects, and it also may specify specific

policies for

individual actions, though those specific individual

policies can be

viewed as part of one whole policy for the service.

4. The process model of a service shows how a

consumer may interact

with (invoke?) specific actions in sequence to

accomplish some business

function aligned with the service's RWE

5. There may be multiple processes in the process

model, involving

different sequences and different functions

6. A consumer may interact with (invoke?) a single

action to

achieve a particular effect (whether that is a

process with one step, or

no process, is an issue I suppose)

7. The mechanism by which a consumer interacts with

a service is by

invoking an action through message exchange; that

is, the consumer and

service exchange information (in the form of a

message) to achieve some

effect

8. Interaction with different actions can be by

different MEPs

9. The decision about service boundaries-which of

all possible

actions should be in a given service's action

model-can be productively

guided by a set of design principles, which the RA

may include at some

future time.  Principles should be carefully and

precisely defined.

The example again is an Employee Time Management

service.  The action

model of this service might consist of four actions:

 add time records,

update existing time records, delete time records,

and view time

records.  A process model for this service may, for

example, indicate

that it makes sense to view time records prior to

updating them.  But,

it is also possible to add time records in

isolation...without any of

the other actions being involved.  The overall RWE

of this service is

management of employee time, but each action has a

separate effect of

independent value to a consumer.  There is no

absolute rule regarding

whether it makes sense to include all four of these

actions in one

service-without more analysis, it is not clear

whether this is a "good"

service model or not.  However, there are some

design principles that an

architect (creator of a concrete architecture) can

apply in making this

determination:  loose coupling, statelessness,

autonomy, abstraction,

etc.

Thanks.

--Scott

________________________________

From: Ken Laskey [mailto:]

Sent: Thursday, October 11, 2007 11:09 AM

To: Scott Came

Cc: 

Subject: Re: [soa-rm-ra] Questions on action model

Scott,

Indeed I do not expect we (and anyone else) will

provide a definitive

cookbook for defining services.  However, it is

exactly those guiding

principles that I think will be valuable and with

which the RA should be

consistent.  Thomas Erl's book may provide a good

starting point.  If

anyone can summarize between now and when I

eventually make it to a book

store (or log into Amazon), we can begin considering

those.

Note when we mention principles, we have to do much

more than use terms

which are familiar but overused and never really

defined.  The RM

specifically took shots at loose-coupling and

coarse-grained.  I also

put agility into that category.  When we state the

principles (assuming

we can), those SHOULD be phrases that convey enough

meaning that they

cannot be automatically misconstrued (by accident or

on purpose) and

then crisply elaborated.

Again, I'm energized to revise the service

description model but have a

long list of household chores to catch up on first.

Keep sending ideas.

Alternately, you can come over and fix the lawn

mower.

Ken

On Oct 11, 2007, at 1:35 PM, Scott Came wrote:

Ken:

Regarding your #1...

I think this kind of specific guidance is best

reflected in a set of

principles.  I don't believe there will be a "one

size fits all" set of

rules that tell you, in every situation, how to

design a service

properly.  The best you can do is identify the

principal forces at

play-those factors that, at a minimum, the designer

should at least

consider when setting service boundaries.  Those

forces are represented

in principles that say what should characterize a

proper service.

Proper application of these principles (selecting

among the sometimes

competing forces) requires the skill of a designer,

but well-stated

principles accelerate the design process and bound

the designer's

discretion somewhat, in pursuit of an overall design

objective.

And not just any old set of principles will do.  SOA

has an overall

purpose-to increase agility, adaptiveness,

responsiveness to change-so

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Ken Laskey

MITRE Corporation, M/S H305      phone: 703-983-7934

7151 Colshire Drive                         fax:       703-983-1379

McLean VA 22102-7508

 

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