[ogsa-wg] ... without wsa:Address profile, AbstractName is meaningless ...

[Steve Loughran]

Frank Siebenlist 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 has been reiterated in a number of emails, but i wanted to call it
 > out separately to facilitate the discussion whether the observation
 > holds water and if so, whether such a EPR-minter Address-profile should
 > become part of the ws-naming spec.

One thing to remember is that WSDM defines every resource as having a 
ResourceId, and says that that ResID must be unique.

So in the CDDLM deploy API we have
  -a resource ID that is used to uniquely identify a created System.
  -an operation on a portal that maps from a resource ID to an address

The latter effectively allows multiple portals to manage the same 
cluster by giving you a more robust means to access things inside it.

However, once you have an entity that can be accessed by >1 Address, you 
have to consider how WS Resource Lifetime interacts. Does the resource 
at address A have the same lifetime as address B: if I go A:<Destroy> 
does that destroy B too? And if the lease to B expires, does A go away 
too? Or do you have to model the thing at the end of every address not 
as the resource with which you are interacting with, but as a transient 
view of the resource, a view with its own lifetime.

-steve

 > PS. Note that everywhere I wrote "Address" above, it should probably be
 > substituted by "Address+ReferenceParameters", but this simplification
 > doesn't change the observation.

that depends on how you implement WSRF. Mine only uses the address, and 
so should in theory interop better with other WS-A implementations. But 
I do use generated GUIDs in that address, as it is the best way to 
guarantee uniqueness.