[dais-wg] WSRF Embodiments and DAIS

[Susan Malaika]

The Oasis WSRF group asked the GGF DAIS working group to consider the WSRF
"WSDL 1.1 Binding Element Embodiment".   An item was posted to the DAIS
mailing list entitled "DAIS mapping and WSRF embodiments" on 23 November
2004. There has been discussion among the DAIS community on the use of the
WSRF embodiments.  Some of the DAIS community involved in the discussions
are the implementers of the first open source version of DAIS known as
OGSA-DAI; they are the first users of DAIS; they are active in promoting
DAIS among data grid communities around the world. These are some interim
conclusions:

1. Multiple kinds of DAIS Users
It is still not clear if DAIS should mandate WSRF because some of the
participants in the DAIS group rely on non-WSRF middleware. DAIS could go
some way towards satisfying WSRF and non-WSRF users by placing the resource
identifier in the DAIS messages (so a single DAIS message format could be
used by both WSRF and non-WSRF DAIS users).
A note on resource properties:

   Resource properties requests cannot include resource identifiers in the
   message body. The resource identifier must be placed in the header.

A  suggestion for the WSRF group :

   It would be helpful to know if specifying a resource identifier in the
   DAIS messages as well as in the header is acceptable to the WSRF folk.


2. Multiple resources in a single request (see below for use cases)
Currently, each DAIS service request accesses a single resource, and the
resource being accessed determines the underlying resources that should be
accessed too, e.g., the exposed single resource can perform resource name
mappings . In this case, the WS-Resource concept may (or may not) be used
to represent the exposed resources in DAIS. (depending on whether DAIS
adopts WSRF)
In some proposed extensions and applications of DAIS, multiple resources of
different types are accessed through a single service request. It is
required that the multiple resources be visible to the client.  The
WS-Resource concept could be used  to represent a collection of resources.
An identifier to represent the collection could be placed in the header,
while the individual resource identifiers in the collection could appear in
the message content.
A note on resource properties:

   Resource properties requests could result in properties for all the
   resources in the collection being examined. (see below for alternatives
   for representing the resource properties documents)

A  suggestion for the WSRF group :

   It would be helpful to know if representing a collection of resources as
   a WS-Resource is a recommended use of WSRF.


3.  WSRF "WSDL 1.1 Binding Element Embodiment"
If DAIS does adopt WSRF then the "WSDL 1.1 Binding Element Embodiment"  is
helpful because it permits a client supplied resource identifier to
appear  in the message header (in other words the resource identifier is
not opaque to the client). However note that there are client side
prerequisites for the "WSDL 1.1 Binding Element Embodiment", e.g., the
client software would have to know to place the resource identifiers in the
right place in the header
A  suggestion for the WSRF group :

   It would be helpful to know if there are any tools that support
   embodiment  "WSDL 1.1 Binding Element Embodiment"

.................................................................

Use Cases
.........
Here are some use cases for multiple resources in a single request:

U1. In an interaction with a DAIS service, many resources may be created to
represent the results of requests.  There may come a time when several of
these resources can safely be removed.  In such a setting, the options are
to:
   U1.1. Invoke something like "remove() => EPR representing resource" for
   each of the resources.
   U1.2  Invoke something like "remove([EPR representing resource-1,
   ...,EPR
   representing resource-n]) => EPR representing service" once.

How would option U1.2 be modeled through WSRF?


U2. In an interaction with a DAIS service, it may be necessary to aggregate
multiple results sets and return the combined result set via ftp.  In such
a setting, the options are to:
   U2.1 Invoke something like "ftp (..) => EPR for resource1"  for each of
   the resources and then aggregate the results on the client
   U2.2 Invoke something like :
         - "aggregate ([EPR  representing resource-1, ...,EPR representing
         resource-n]) => EPR representing service"
         - "ftp (..) => EPR representing aggregated resource"
         (the result aggregation would be done at the server.)


How would option U2.2 be modeled through WSRF?
   (BTW it is possible that a combined aggregate and ftp operation would be
   desirable)



U3. In an interaction with a DAIS service, it may be necessary to issue a
query over multiple databases and files.  In such a setting, the options
are to:
   U3.1 Invoke something like "query (..) => EPR for resource1"  for each
   of the resources, returning each query result to the client, and then
   aggregate the results on the client
      (the result aggregation process could be very complex.)
   U3.2 Invoke something like "copy (..) => EPR for resource1"  for each of
   the resources and then issue the queries locally on the client
      (this means having a query engine on the client.)
   U3.3 Invoke something like "query([EPR  representing resource-1, ...,EPR
   representing resource-n]) => EPR representing service" once
      (the query result aggregation would be done at the server.)

How would option U3.3 be modeled through WSRF?



Alternatives for modeling resource properties documents  for U1.2, U2.2,
U3.3
.............................................................................
<ResourceNames>
        <ResourceName>resource1</>
        <ResourceName>resourceX</>
</>

Or as complex as

<Resources>
        <Resource>
                <ResourceName>resource1</>
                <ResourceType>RDB</>
                <ResourceSchema>....</>
        </>
        <Resource>
                ...
        </>
</>

A  suggestion for the WSRF group :
   It would be helpful to know which modeling approach is preferred


Thanks to everyone who contributed and reviewed this note. Happy Happy
Holiday Season :-)

Susan Malaika
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