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

[David Snelling]

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.
>
> 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.
> 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
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