[ogsa-wg] Data architecture requirements on naming

[Dave Berry]

Dear All,

Recent discussions on the OGSA data architecture have raised two use
cases that may affect the naming discussion.  Both involve the mapping
of one "abstract" (for some meaning of "abstract") name to multiple
possible "concrete" names.  A further step is then required to choose
the best "concrete" name, according to the policies required by the
client.  We are wondering whether the WS-Name/EPR resolution services
can be modified to support these functionalities.

Note: here, "abstract" names may or may not have the same meaning as
abstract names in the proposed WS-Names spec.  This is an issue that
needs clarification.

Case 1 is when we are dealing with replicated data.  It is common to
have an "abstract" name that represents a given file, table or query
result that is stored someone in the system.  This is then resolved to
one of multiple copies.  The client typically wants the copy with the
best response time (which will be some function of latency and
bandwidth).

Case 2 is when we are dealing with data stored at a certain location and
the data may be accessed by several different protocols (e.g. GridFTP,
HTTP, ...).  The client (or transfer service) wants to map the
"abstract" name to the fastest protocol that it can handle.

In each case, we could take one of two approaches:

(A) resolve the "abstract" name to a list of "concrete" names, and use a
separate selection service to choose among them

(B) pass the appropriate policy specification to the resolver service,
which will then return the appropriate "concrete" name. 

Note: (B) could be considered (and even implemented) as a composition of
the resolver and selection services in (A).

Would it make sense to specify either one of these functionalities as
part of the resolver services considered in WS-Naming?  E.g. the
operations could return a list instead of a single EPR (option A) or
they could return a single EPR as now but take a policy argument (option
B).

Best wishes,

Dave Berry
Research Manager, National e-Science Centre
15 South College St., Edinburgh
Tel: +44 131 6514039