[ogsa-wg] Once upon a time or two ...

[Dave Berry]

There are many issues in this discussion that I don't understand , and
this seems a key one.  Perhaps the participants could read the following
and set me straight?

The W3C guidelines on the use of URIs (and hence, I presume, IRIs) is
that each resource should be identified by a different URI.  URIs can be
compared.  URIs should not be reused to refer to different resources.  

I don't know whether these guidelines are adhered to in practice, but on
paper they seem to provide the uniqueness and comparison functionality
that we require.

The problem seems to be that WS-Addressing (or perhaps just some uses of
it, e.g. some implementations of WSRF) breaks this nice system, by using
the URI to name the access mechanism (the web service) rather than the
resource being addressed.  Frank has suggested on a couple of occasions
that we specify how a unique address can be reconstructed from the
wsa:to field and the parameters.  Given this step, I would assume that
the scenario that Frank considers here would not be permitted:

> > An EPR-minter can decide to create a new EPR for a resource and
reuse 
> > an Address that was used for an other resource before.

So, I have many questions:

1. Is the above characterisation an accurate rendition of the W3C
position on URIs and IRIs?
2. Do we want stricter limits than the W3C?
3. Can we profile WS-A as Frank suggests?
4. If (3 and not(2)), does that satisfy our requirements?

Another advantage of URIs is that publishers are permitted to use their
structure to pass back server-specified information and clients are
permitted to parse URIs to extract this information.  So an LSF system
could include the job-id in a certain part of the URI and clients can
extract it as necessary.  (Although one could argue whether that was any
neater than adding a specific XML field).

Best wishes,

Dave.

> -----Original Message-----
> From: owner-ogsa-wg at ggf.org [mailto:owner-ogsa-wg at ggf.org] On 
> Behalf Of David Snelling
> Sent: 18 November 2005 15:12
> To: Frank Siebenlist
> Cc: ogsa-wg; ogsa-naming-wg at ggf.org
> Subject: [ogsa-wg] Once upon a time or two ...
> 
> Folks,
> 
> Once up on a time or two Frank wrote:
> 
> > Without the proper uniqueness guarantees for the 
> wsa:Address, the use 
> > of ws-naming's AbstractName is meaningless.
> >
> > The EPR with an embedded AbstractName essentially describes 
> a binding 
> > between the Address and the AbstractName.
> > One could argue that this binding is a bit of a flaky assertion 
> > without any way to specify time-validity or issuer.
> > As a result, one can not see from an EPR alone when it was 
> issued or 
> > whether it is still valid or not.
> >

> > This would yield the undesirable situation that you would have two 
> > EPRs with identical Addresses and two different AbstractNames 
> > associated with different resources, and the client would 
> have no way 
> > to see which one of the EPRs is valid...
> >
> > For example, if I have two EPRs with the same Address, 
> where one EPR 
> > includes an AbstractName that identifies MyBankAccount and 
> the other 
> > includes an AbstractName identifying YourBankAccount, then 
> one of us 
> > will not be happy with that situation...
> >
> > In order to avoid this ambiguity, we need the guarantee from the 
> > EPR-minter that Address values will not be reused for different 
> > resources: for all times, the Address should either refer 
> to that one 
> > and only resource, or it should be invalid (and it is allowed to 
> > change between those two states).
> > Furthermore, the EPR-minters should ensure that globally unique 
> > Addresses are used for a resource such that different 
> EPR-minters do 
> > not (accidentally) use the same Address for different resources.
> > The described uniqueness properties of the Address constitutes a 
> > required EPR-minter profile for the use of AbstractNames.
> >
> 
> This issue has yet to be addressed to my satisfaction. There 
> have been 
> a number of email exchanges in response to it on several 
> occasions, but 
> none of these threads actually deal with the issue.
> 
> Put simply, if you don't put globally-unique-in-space-time 
> requirements 
> on your address (GSR in OGSI speak*) then any similar 
> requirements you 
> put on an Abstract Name (GSH in OGSI speak) are wasted.
> 
> I believe that answering this issue will help clarify many of 
> the other 
> threads (miss) associated with this issue.
> 
> In particular, I believe Frank is right. Therefore, if an EPR 
> is going 
> to be a WS-Name, the wsa:Address MUST have the same uniqueness 
> properties as the Abstract Name. Then if the answer to the question, 
> "Why do this uniqueness stuff twice?", is "I don't know!", then it 
> seems logical to me that a WS-Name is a profiled EPR along the lines 
> proposed by Tom M.
> 
> Thoughts?
> 
> Historical Footnote:
> 
> * Note: OGSI addressed this issue in GSRs by requiring that clients 
> could detect when the GSRs were stale and that services 
> reject them if 
> a client attempted to use them. GSHs had uniqueness 
> constraints placed 
> on them.
> 
> -- 
> 
> Take care:
> 
>      Dr. David Snelling < David . Snelling . UK . Fujitsu . com >
>      Fujitsu Laboratories of Europe
>      Hayes Park Central
>      Hayes End Road
>      Hayes, Middlesex  UB4 8FE
> 
>      +44-208-606-4649 (Office)
>      +44-208-606-4539 (Fax)
>      +44-7768-807526  (Mobile)
> 
>