owner-ogsa-wg@ggf.org wrote on 08/31/2005 12:11:00 AM:
2-cents: It is my understanding that EPRs can't by themselves be guaranteed to be unique or that bit-wise comparisons are unreliable considering canonicalization and embedded metadata issues.
That is correct
If so, then a unique AbstractName is needed in order to accurately resolve EPRs, especially considering the potential service migration.
I think that AbstractName is certainly one approach to solving this problem. Remember that ReferenceParameters are used to provide information to the RECEIVER(wsa:to) to disambiguate the resource for dispatch. Obviously, in order for the refParams to be useful they should be unique (in some context). The wsa:to provides the context in this case. I can envision lots of service migration scenarios that could take advantage of the above fact and would ensure that the ResolverEPR was correctly informed of the migration (change in wsa:to URI).
Instead of mandating, perhaps the speficiations can recommended the use of WS-Naming? Specifications could still accept EPRs and implementations can check them for the presence of an AbstractName and take advantage of it if available (internal hash table, etc).
Agree with this statement. In essence, if a service requires the ws-naming claim it can check for it...
Ian Foster wrote: Dave:
My "proposal" was just a request that we have the "resolver EPR" in a separate specification.
However, in a bit more detail, here are my opinions in this area:
1) The BES specification should just use EPRs, and not mandate the use of WS-Naming AbstractNames.
Rationale: Such a requirement imposes a cost on BES users that they may not want to pay--for a benefit that they may not require.
Mandating the use of WS-Naming names imposes an overhead in terms of both time (the cost of generating the AbstractName) and space (the storage that it requires).
Yet:
a) I may not need to perform the equivalence test that AbstractNames are introduced to allow. (E.g., I haven't thought deeply about this--but I can't recall that we've ever encountered that need.)
b) I may need to perform an equivalence test, but not require the "globally unique in time and space" constraint that WS-Naming requires. [This constraint presumably constrains the form of the name that I can create, preventing me, for example, from using user- supplied strings.]
c) I may need to perform an equivalence test, but want to do that at a different level: e.g., I may already maintain my own table of jobs for some other purpose, so the WS-Naming AbstractName just replicates unique data that I am already maintaining.
If people WANT to pass around EPRs that have these AbstractNames in them (or other similar constructs with different constraints/semantics: e.g., "unique within my VO"), all power to them: but I don't see a reason to require this in BES or any other specification.
2) We should have a separate specification for the "resolver EPR" (and associated Resolver portType) and the "AbstractName" concept.
Rationale: The "resolver" EPR is useful in a wide range of situations independent of the specific name syntax and semantics described in WS-Naming.
I can imagine lots of places where I might use a resolver EPR. E.g., maybe in the BES case my jobs can migrate, and so I want the EPR that I get back to include a resolver EPR that I can use to determine its new location. But as noted above, I don't necessarily need an AbstractName in the BES case.
Similarly for relocatable services: maybe I'll do a metadata query on a registry to get a service EPR (with a resolver EPR in it), then if the service is not where the registry says, contact the resolver to determine its new location. Again, I don't see that I will need AbstractName semantics here.
Thus, given that we have two concepts that seem logically quite distinct, and that are certainly distinct in terms of when and how that will be used, I argue that they should be separated.
3) You also asked about three levels and about "human-oriented" vs. "abstract". These concepts are not in the WS-Naming spec, but for what it's worth, I don't see them as useful or relevant here. People use many sorts of "names" of different sorts, and they don't cleanly separate into three levels or into "human-oriented" or "abstract". E.g., if I'm implementing a replica location service, I often want to map first from a "logical file name" to a "site name" and then from there to a "physical location." Furthermore, if you build a system of this sort, you have to allow people to stick whatever names are convenient for them in at each level, because often these names come from elsewhere. Some users may make some of these names "human-oriented", others may not--it shouldn't matter to the service.
Regards -- Ian.
At 08:58 PM 8/30/2005 +0100, Dave Berry wrote: Ian,
I wonder whether you or one of your team could write a note about the background to your proposals? It would help me to understand how they fit into the wider architecture. At present I don't feel able to make an informed contribution to the discussion.
The current shape of OGSA (if I can call it "current" without biasing the discussion) has three concepts relevant to this discussion:
1. Three levels of naming (human-oriented, abstract, and address). 2. An implementation of abstract names as an EPR containing a string and a resolver. 3. A service interface for BES that takes abstract names as parameters.
Each has associated questions raised by your concerns:
1. Do you want to have fewer levels of naming across the architecture or are you happy with the three listed here?
2a. Are you happy that abstract names should be represented in this way? 2b. What would a "resolver without an abstract name" resolve? When do you need it in addition to or instead of an abstract name? Does it fulfill a different function or is there some overlap?
3. What should the BES interface accept instead of or as well as abstract names? When do you need this functionality? How should the interface cope with the different types of entity?
I can make a guess at part of these answers but I'd rather read an explanation from the horse's mouth.
Best wishes,
Dave.
-----Original Message----- From: owner-ogsa-wg@ggf.org [mailto:owner-ogsa-wg@ggf.org] On Behalf Of Ian Foster Sent: 30 August 2005 04:02 To: Tom Maguire Cc: Andrew Grimshaw; ogsa-wg@ggf.org Subject: Re: [ogsa-wg] BES query
I'm interested in that question too. As I've said on quite a few occasions, I like the EPR + ResolverEPR (as in the original WS-RenewableReferences) -- that is a nice simple mechanism. I don't understand why we can't have this in a separate specification.
Ian.
So just to get some nomenclature correct. By WS-Names we mean an EPR that is profiled to contain both a ResolverEPR and an AbstractName. So what do we call an EPR which just contains a ResolverEPR?
Tom
Ian Foster wrote:
I believe that the opinion was expressed by some at the San Diego meeting (e.g., by Steve Tuecke) that WS-Names should NOT be mandated.
It certainly defines a nice way of using EPRs that will be useful in some situations. But it surely can't be the case that we always want to mandate this particular set of extensions to EPRs. That requirement certainly doesn't jibe with how we use them in all cases, for example.
Ian.
At 09:25 AM 8/29/2005 -0400, Andrew Grimshaw wrote:
All,
In the BES working group call last week the issue of naming came up. The current DRAFT specification calls for passing WS-Names in and out of
At 09:23 PM 8/29/2005 -0400, Tom Maguire wrote: the
various function calls. There was the question as to whether EPRs is all that should be specified. We thought this is an OGSA issue: mainly is
OGSA endorsing the use of WS-Names where appropriate. Clearly I think we should. But this should be discussed.
Andrew
_______________________________________________________________ Ian Foster www.mcs.anl.gov/~foster <http://www.mcs.anl.gov/%7Efoster> Math & Computer Science Div. Dept of Computer Science Argonne National Laboratory The University of Chicago Argonne, IL 60439, U.S.A. Chicago, IL 60637, U.S.A. Tel: 630 252 4619 Fax: 630 252 1997 Globus Alliance, www.globus.org <http://www.globus.org/>
_______________________________________________________________ Ian Foster www.mcs.anl.gov/~foster Math & Computer Science Div. Dept of Computer Science Argonne National Laboratory The University of Chicago Argonne, IL 60439, U.S.A. Chicago, IL 60637, U.S.A. Tel: 630 252 4619 Fax: 630 252 1997 Globus Alliance, www.globus.org _______________________________________________________________ Ian Foster www.mcs.anl.gov/~foster Math & Computer Science Div. Dept of Computer Science Argonne National Laboratory The University of Chicago Argonne, IL 60439, U.S.A. Chicago, IL 60637, U.S.A. Tel: 630 252 4619 Fax: 630 252 1997 Globus Alliance, www.globus.org
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