Ian, As always, you raise interesting questions. Some I want to ask you about further; some I would like to see other people address. However, I was surprised by your reply about the "three levels" of naming. While WS-naming doesn't include these concepts, the OGSA v1.0 document does. They also form the basis of the GFS working group work that led to RNS and WS-Naming, and are important parts of EDG/EGEE, for example. That doesn't mean that you have to agree with it but I'm surprised that this issue wasn't resolved earlier. I'm also surprised that you give name equivalence as the main characteristic of an abstract name. I thought the main characteristic was that it was a persistent name that does not specify a particular location. (Although this could be a property of the WS-Name package rather than the string - see below). I'm afraid I don't follow your example of a file replication system. Clearly we need to name the separate entities involved and there may be many levels of indirection. I don't see why that is an argument against the three level approach. We don't need to have one "level" of name for each "level" of indirection. Turning to a question I'd like to see other people address: Ian's point about uniqueness within a particular context makes good sense to me. If a WS-Name is a combination of an arbitrary string and a resolver, isn't it the combination of the two that should be globally unique? E.g. if one WS-Name resolves "foo" to my hard drive and another resolves "foo" to Ian's, the two WS-Name packages themselves are still globally unique. I suppose this is why Ian took name equivalence as a key property. Do we perhaps need a scope notion in WS-Names, so that they may be valid within a VO, or globally unique, or have some other scope? I guess the counter to this is whether it is really such an imposition to create a globally unique string, given that UUIDs seem to do the job. Dave. -----Original Message----- From: Ian Foster [mailto:foster@mcs.anl.gov] Sent: 31 August 2005 00:35 To: Dave Berry; Tom Maguire Cc: Andrew Grimshaw; ogsa-wg@ggf.org Subject: RE: [ogsa-wg] BES query 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. At 09:23 PM 8/29/2005 -0400, Tom Maguire wrote: >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 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 <http://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 <http://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 <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 <http://www.globus.org/>