Michael,
I think the more important point is that the descriptions are not isolated entities but leverage common resources and each other, so a collection of descriptions should tell you more (OK, at least as much) about the subject than you get from any single description.
Ken On Oct 16, 2007, at 11:44 AM, Poulin, Michael wrote: Thank you, Ken. I think we have agreed with Danny that multiple descriptors make sense in multiple business domains/contexts and/or multiple registries/repositories. This, probably, may be reflected in the RA. - Michael 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 Important: Fidelity Investments International (Reg. No.1448245), Fidelity Investment Services Limited (Reg. No. 2016555), Fidelity Pensions Management (Reg. No. 2015142) and Financial Administration Services Limited (Reg. No. 1629709, a Fidelity Group company) are all registered in England and Wales, are authorised and regulated in the UK by the Financial Services Authority and have their registered offices at Oakhill House, 130 Tonbridge Road, Hildenborough, Tonbridge, Kent TN11 9DZ. Tel 01732 361144. Fidelity only gives information on products and does not give investment advice to private clients based on individual circumstances. Any comments or statements made are not necessarily those of Fidelity. The information transmitted is intended only for the person or entity to which it is addressed and may contain confidential and/or privileged material. If you received this in error, please contact the sender and delete the material from any computer. All e-mails sent from or to Fidelity may be subject to our monitoring procedures. Direct link to Fidelity’s website - http://www.fidelity-international.com/world/index.html
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" <klaskey@mitre.org> 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:danny_thornton2@yahoo.com] Sent: Thursday, October 11, 2007 3:55 PM To: Scott Came; soa-rm-ra@lists.oasis-open.org 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 <scott.came@search.org> 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:klaskey@mitre.org] Sent: Thursday, October 11, 2007 11:09 AM To: Scott Came Cc: soa-rm-ra@lists.oasis-open.org 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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