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Subject: [dais-wg] WSRF Embodiments and DAIS
To: dais-wg@gridforum.org, wsrf@lists.oasis-open.org
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From: Susan Malaika <malaika@us.ibm.com>
Date: Fri, 17 Dec 2004 02:21:15 -0800
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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