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RE: [asap] questions/concerns on initial working draft doc (and scope)
Title: RE: [asap] questions/concerns on initial working draft doc (and scope)
Keith,
I enumerated your
paragraphs in order to separate my answers:
Re
#1: It's not about terminology. I am concerned about monitoring and
state/properties update support being principal requirements for ASAP
compliance, as it requires stateful implementations.
Re
#2: Agree. I re-read your definition and "method" should be renamed to
"operation".
Re
#3: Yes, I do. That's the reason I joined this TC
:-)
IMHO, there's a need
for standard protocol
- defines how the originatorURI (compliant with
WS-Addressing) is going to be passed to the async WS,
- defines correlator
ID and its use (misc. issues incl. ID format, passing as a part of
the header vs. as a part of the message, correlation scope,
etc.)
- defines "standard"
notification message(s) (to be defined in originator-published WSDL) and generic
extensible format for "results" part of
notification
- deals with
uncorrelated notification and request with multiple responses (here it's more
about correlation scope)
- and optionally
(these require stateful implementation):
-- defines
monitoring support
-- defines service
lifecycle management (i.e. instantiation, state/props change, termination,
post-completion results query, etc.)
-- "completed"
notification without attached results (both as a WS message, and a non-WS
HTTP Req with predefined header)
--
...
I don't think it's
possible to solve these problems with a basic SOAP, but I will consult my WS
development team for a feedback.
Re
#4: Why persistent? Is it a requirement? Your definition of "context
data" here extends one in the document:
Context
data: The XML data sent to initiate the
service.
Results
data: The XML data created by the
successful completion of the service.
...
When reading the
document, I concluded that it's about "Request data" and "Response data" as per
WS terminology. If the group chooses to keep these terms/concepts, I
suggest changing the definitions to avoid confusion.
Re
#5: It's defined by the logic supported in WS implementation. In our
Realtor WS demo the notification is turned off when the client is declared
inactive (e.g. purchased the property).
Re
#6,7,8: All these are implementation specific. Same as
#5.
Keith,
all,
My suggestion is
that we seek input from everyone in the group on their view of the
scope/direction for the ASAP. The ideal solution would be for each one to
come up with the list of items they would like to see included in the spec and
post them to the list. Next we can rank them and work on defining the scope
according to the rank/priority.
Thanks,
Michael Shenfield
Advanced Research Group
RIM
905-629-4RIM x4347
____________________
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-----Original
Message-----
From: Keith Swenson
[mailto:]
Sent: October 7, 2003 7:35
PM
To: Michael Shenfield; Keith Swenson
Cc: ASAP
(E-mail)
Subject: RE: [asap] questions/concerns on initial working
draft doc (and scope)
Let
me try to refocus this discussion.
ASAP does not specify how you implement the web
service. If you wish to use J2EE, you may use whatever
technique. I thought that describing in terms of stateful/stateless
would help in understanding the concepts, and to distinguish the various
meanings of the word 'asynchronous'. I didn't mean to imply that this
was the actual implementation. ASAP does not proscribe how this is
implemented in the J2EE world, and so I don't want to discuss this
here.
I still think "method" in the spec refers to an
operation, because it consists of a request message and a response
message. The messages are described, in places, as
parameters. Please point out in the document where it means something
else than this. I propose that we change "method" to "operation" in
the document in order to conform with SOAP
terminology.
Let
me ask you a question: do you believe that a special protocol is needed for
an operation that can not be monitored? For example, a service that
you send a message to, and a while later you get a response from. No
possiblity to change you mind. No possiblity to monitor status.
Can't you do this is basic SOAP protocol? Let's discuss if you think
differently, but I am going to assume that this is covered by basic
SOAP.
The
"context data" is persistent data that exists in the service instance.
It can be sent as part of a reqeust (e.g. SetProperties), or as part of a
response (e.g. GetProperties). Furthermore, there are messages that
contain the schema of this context data as part of a response from the
factory object.
We
really should discuss usage scenarios. You touched upon the realestate
example, one of my favorites. You describe the service as being a
recurring query for houses that meet a specific criteria. The context
data includes the query, as well as the result set. (You might implement
this any number of ways, but for now lets imagine that we choose this
one.) The client would make a simple SOAP request to start this
service, giving both the initial query, as well as the address to send
responses to. Everytime the result set changes, a notification is sent
to the client. It would be really unpleasant if there was no way for
the client to turn this off. When you started the service, you had no
idea how long you would be searching. You in fact might put the serach
end data as a context variable. Later, you can change that end date by
using "SetProperties" thereby extending the duration of the search service,
or ending it early. You can also cancel the service by using the
"ChangeState" to the closed state (which is the terminal
state).
The
client of this service need only know the name of the context variable that
holds the query (e.g. "query"), and the name of the context variable that
holds the results (e.g. "listings"). Probably, the service instance
would not allow the client to set the value of "listings". Attempts to
set this would result in an error. Some services can not allow
changing of context variables at any time, so attempts to set any of them
would cause an error. In this sense, the operation "SetProperties" is
optional. It is not really optional, but can be implemented to simply
return an error.
If
you don't have a client that can receive notifications, then you also can
simply pick up the latest value of "listings" at any point in time. In
this case you would not register an observer address. Also, you would
never receive a completed message.
Finally, others interested in the same listings (the same query)
could register to receive notifications of when the listings change.
Note: you are not registering to a specific query, because the query could
be change. Instead you are registering to a specific instance of the
service.
Now,
can we start over with the questions because I am having a hard time
deraveling them from the discussion below.
-Keith
-----Original Message-----
From: Michael Shenfield
[mailto:]
Sent: Tuesday, October 07, 2003 12:26
PM
To: Keith Swenson
Cc: ASAP
(E-mail)
Subject: RE: [asap] questions/concerns on initial working
draft doc (and scope)
Keith,
I went back to EJB spec to validate my point on
stateless (vs. stateful) session beans. The following is from an EJB 2.1
final draft (section 1.2. What is New in EJB
2.1):
"We have
added support for web services. We have added the ability for a
stateless session bean to implement a web service endpoint. We have added support to
allow all enterprise beans to utilize external web
services."
In the
current J2EE/Java world only servlets and STATELESS session beans could
implement a Web Service endpoint. Neither can support the protocol described
in a current working draft (actually it's not true, one can come up
with a model when the state is shared by servlet instances using a
ServletContext object. It could be a sneaky way to implement monitoring
but very inefficient and non scalable
one)
Cheers,
MS
-----Original Message-----
From: Michael Shenfield
Sent: October 7, 2003 2:42 PM
To: Keith Swenson; ASAP
(E-mail)
Subject: RE: [asap] questions/concerns on initial
working draft doc (and scope)
Keith,
My
comments/answers are embedded in the orig. message. I suggested at the
last conference call that we define the scope of ASAP to clarify what this
spec is going to be about. It looks like we have different views on what
it should cover.
Thanks,
Michael
Shenfield
Advanced
Research Group
RIM
905-629-4RIM x4347
____________________
This information is transmitted on a "WITHOUT PREJUDICE" basis. It
is intended only for the person or entity to which it is addressed and may
contain confidential and/or privileged material. Any review,
retransmission, dissemination or other use of, or taking of any action in
reliance upon, this information by persons or entities other than the
intended recipient is prohibited. If you received this in error, please
contact the sender and delete the material from any
computer.
-----Original Message-----
From: Keith Swenson
[mailto:]
Sent: October 7, 2003 1:37
PM
To: Michael Shenfield; ASAP (E-mail)
Subject: RE:
[asap] questions/concerns on initial working draft doc (and
scope)
The whole point about ASAP is to set up a 'contract' to
have something done and to be able to check on its progress. [Michael
Shenfield] Re: "be able to check on its progress":
Then the name is misleading. The
spec should either be limited to dealing with async Web
Services that support monitoring (I see it as a
small fraction) or to make monitoring optional. From the wireless
standpoint perspective monitoring is a waste of valuable resources, for
the "wired" client it could be useful but requires much more
complex implementation of a Web Service. As already pointed out, the
scalability will take a major hit as Web Service instance cannot be
stateless anymore.
Perhaps more important is the
ability to change your mind and cancel it. [Michael
Shenfield] Again, it's up to the group, but I don't think of it as
a solid requirement. These are all things that need a
"correlation" id of some sort. What ASAP oes it provide a simple
way to request something to be done and receive a correlation id that
can be used to check onthe progress.
There are many use cases that fit this model, but there
are also many that do not. A "stateless session bean" is a pattern
that ASAP is not designed to support. Instead, ASAP is designed
for the "stateful session bean" where you have a unique instance with an
ID, and subsequent requests go back to that same instance. This
session bean is endowed with a goal, and it is expected to last until
that goal is accomplished, and then a little while after that (see the
timeout setting). The goal could be "search four house listings
for 3 months" or something abstract like that. [Michael
Shenfield] The general agreement in a Web Services J2EE
world is that Web Services should only be exposed by servlets or
STATELESS session beans - there're tons of references on the
topic. I am not aware of any implementations of Java Web Services
running as stateful session beans (reasons: scalability, thread safety,
management/sharing issues, etc.)
For many implementations of ASAP, the factory will be
like a stateless session bean in that it is a web service that simply
"exists" and the starting and stopping of it is invisible to the outside
world. The "service instances" then have a lifecycle that can be
externally monitored.[Michael Shenfield] I don't have any problems with a
COMesque "CreateInstanceRq", I've used it for years in COM, as well
as Home interfaces' "ejbCreate" in EJB. I just don't see Web Services
following the same pattern, being involved in many Web Services
activities I haven't seen many that mandate user managed instance
creation. The other reasons are as per previous
comments.
The concept of "fire and forget" (uncorrelated
messages)[Michael Shenfield] "fire and forget" mode is a
user experience term. The message request and response(s) share same
correlation ID.
is probably not what ASAP is designed to support.
This would be a single call that later returns a result (or multiple
results). This seems like it can be handled sufficiently with
(reliable) asynchronous messaging. In this case you do not need a
correlation id, because there is no other communications with the
instance. As you point out, these do not need monitoring or other
support. Lets discuss this.
As for the concept of "multiple async responses", this
is quite definitely what ASAP is designed for. There is no reason
that ASAP is restricted to a single response at the end. Once the
correlation key is set up, the services on both sides can make further
requests to each other. The simplest way to implement this is
every new result causes a change notification event back to the
observer. The event might (or might not) carry the new data.
If the event does not carry the data, the observer can do a
"GetProperties" in order to fetch the changed data. The former
implementation is most likely to work with a generic ASAP
implementation, but people are alowed to extend the ASAP protocol to
include special methods, e.g. "NewSearchResult". In this case the
ASAP sets up the basic instance which represents the agreement between
the client and realtor, and then the services can inspect the interfaces
supported, and if they both understand this extended command, they use
it.
Use of ASAP in the above example would allow the client
to modify the type of house they are looking for (after receiving a
bunch of uninteresting results) or terminate the search (in case they
find their dream house).[Michael Shenfield] see comment
#2
Terminology is always a big problem. We used to
call them "interfaces" and now we call the "port types". I think
that our usage of "method" should be "operation" now, right? [Michael
Shenfield] No, method in your definition means "message".
Operation is defined as a set of Requset, Response, and
Notification messages
If you see
things like this that obvisouly deviate from the SOAP norm, please bring
these up. Our goal is to be consistent. "Context data" &
"result data" on the other hand is a concept unique to ASAP for which
there is no other term (unless I have missed something). [Michael
Shenfield] Web Service operations are defined using Request and
Response (if any) messages. I think "Request data" and "Response data"
if you want to define parts (or group of parts) will be more
consistent.
These are parts of messages, but the key is that these structures
persist in the service instance, and can be queried and (in some cases
modified) by later operations.
BTW: We are designing Wf-XML as an extension of ASAP,
and in that the Factories themselves can be created and started.
This maps into the BPM ability to define and start new business
processes. ASAP is extended to add the new methods for the
'factory lifecycle'.
-Keith Swenson
(408)
456-7667
-----Original Message-----
From:
Michael Shenfield [mailto:]
Sent: Tuesday, October 07, 2003 9:45 AM
To: ASAP (E-mail)
Subject:
[asap] questions/concerns on initial working draft doc (and
scope)
Hi all,
At the last conference
call we had a discussion on taking the initial working draft to the
general public. I suggested 'no' based on my initial impression from
scanning through the document 2 weeks ago. Finally, past weekend I was
able to review the document in detail. Here's the list of questions
and/or concerns that I would like to post here for your
review:
- Factory "resource".
I am not
sure about the concept of "factory" and passing observerURI as a part of
CreateInstanceRq. Let's take Java Web Services as an example. When a Web
Service deployed as a servlet the hosting Web Server container plays the
role of the "factory" but this is "invisible" for the caller. The caller
posts to the WS endpoint URI an HTTP request that contains the SOAP
message to be invoked. Lifecycle management of the servlet (as a WS
instance) is not covered by invocation protocol and therefore "creation"
of the WS instance is non of the caller's concern. Similar model stands
for the Web Services deployed as stateless session beans, the EJB
container hides the creation process. For all async Web Services
deployed at RIM (to support application initiated push to a wireless
device) we have an "observer" URI (or rather requestor endpoint) passed
as a part of the Web Service message. The requestor URI could also be
submitted at registration (optionally with a correlationID), so that all
following correlated and uncorrelated notifications could be posted to
the requestor endpoint. This opens the stage for the next
question:
- Multiple async responses for a single request or
uncorrelated notification messages.
One of the
possible deployments for async Web Services is when a single request
causes a number of responses. As an example, one of our demo Web
Services "Realtor" uses this model to send listings to a real estate
agent registering a new client. The model is obviously asynchronous as
we don't want our real estate clients wait (and pay for the airtime)
till the request is processed. The "client registration" message is a
request that carries the client search information, requestor endpoint
URI and generated correlator ID to be used for responses. The server is
doing the search in MLS and asynchronously sends found listings each in
a separate SOAP message (here we have multiple responses for a single
req). Moreover, when a new listing is posted to MLS the server is
searching for interested clients and sends the listing to their agents
as a notification (correlated notification model). Additionally, the Web
Service is capable of sending uncorrelated notifications. We implement
the following model: when real estate agent is logging in, the Realtor
Web Service gets endpoint URI of the service proxy (linked with the
device) and when a new information for the agent is available in the
server (e.g. viewing appointment), the Web Service sends uncorrelated
notification to the endpoint URI. In my opinion both models (multiple
async responses and uncorrelated notification) should be included in the
scope of ASAP
- Monitoring support.
In the
document there is a lot of discussion on monitoring the execution
process and changing the state/properties during execution. I am not
sure if this should be mandatory for compliance, one can perfectly
deploy the async Web Service without support for monitoring or state
change (see example above). Moreover, as an implementer I am not clear
on how to implement this monitoring and state altering model in a
scalable Web Service - in my opinion it contradicts basic scalability
considerations of J2EE or .NET deployment. I think that ChangeState,
GetProperties, SetProperties, and StateChange msgs should be changed to
optional. As for Subscribe, Unsubscribe, and Completed, I am looking
forward to the discussion on how it should be defined in the ASAP
context.
Introducing monitoring of the execution is identical to
polling for the completion/result and kills async efficiency. I
understand the async paradigm as the model where requestor "calls and
forgets". The implementation (and ASAP spec) should guarantee that the
requestor gets the results (or notified on completion) when ready. Am I
missing something here?
- Introduction Section. Language and terminology.
It looks like the verbage of section 1 intentionally
deviates from the standard Web Services terminology and definitions. Is
there a reason for this? Why should we call SOAP messages as "methods",
Request data as "Context data", Response Data as "Results data", etc.
Again, I might be mistaken here but my impression was that ASAP is
strictly about Web Services?
Sorry to send this 20 mins prior to the conference call,
but as I didn't see posted agenda we can as well discuss these
points.
Cheers,
Michael Shenfield
Advanced
Research Group
RIM
905-629-4RIM
x4347
____________________
This information is transmitted on a "WITHOUT PREJUDICE" basis.
It is intended only for the person or entity to which it is addressed
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retransmission, dissemination or other use of, or taking of any action
in reliance upon, this information by persons or entities other than the
intended recipient is prohibited. If you received this in error, please
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