Title: RE: [asap] Factory in ASAP
>> Your other example is with 1,200,000,000 operations. Again I am puzzled.
>> Why not to have just 4 operations Create, CheckStatus, Change, and Cancel
>> while passing an SSN as a parameter(part)?
Of course, in this case it would probably be better to do what you suggest.
The example was bad, but all I was using it for was to show that factories can
be "virtual". A better example might be that the factory address includes the
name of a Java class which is a servlet to be invokved. Or it even could specify
the method on a particular class. The point is that there does not need to
be any additional overhead just because there are a number of "factories".
>> I think the mechanism of Web Service instantiation
>> should be left to framework providers.
Of course it should. Please don't confuse the creation of a web service
with the creation of an Asynchronous Service Instance. Creating an instance
of the service, is not really creating a new web service. Just like creating
and instance of an object is not creating any new methods.
>> We have prototype Web Services ... and nowhere had to worry about "factories"
As I mentioned, there are an unlimited number of ways to do things. The need for
factories comes only from wanting to link to systems that expect factories.
You probably never did this.
Let me repeat my request from before: Describe what must be done to link
two systems at run time together such that one can start a long term process,
update it later, check its status, and terminate it if necessary. It is from
the dynamics of this linking that the advantages of this approach appear.
(And think back to the beginning of the OO days when all the programmers
were pointing out that any program can be written without using OO constructs.
The difference lies not in the program, but in the ability to reuse it in
many different situations.)
-Keith Swenson
P.S. We have some unfinished issue from an earlier conversion. I was hoping that someone else would chime in, but since they have not I will follow with a separate message.
-----Original Message-----
From: Michael Shenfield [mailto:]
Sent: Thursday, November 06, 2003 8:17 AM
To: 'Keith Swenson'; Mayilraj Krishnan; Jeffrey Ricker
Cc: ASAP
Subject: RE: [asap] Factory in ASAP
Wow...that's a long email. I had a hard time reading it on my Blackberry at
breakfast :)
Now to the point. I don't think anybody argues the importance of "Resource
Oriented" approach, that's why people define multiple Web Services (and
ports) instead of offering just one Web Service with a large number of
operations. Your analogy with object-oriented vs. procedure-oriented?
True...the concepts are related somehow. My question is what it all has to
do with the Factories? Your example on car repairs only shows that one has
to define two web services "CarRepairAppointment" and "AccessoryOrder". Your
other example is with 1,200,000,000 operations. Again I am puzzled. Why not
to have just 4 operations Create, CheckStatus, Change, and Cancel while
passing an SSN as a parameter(part)? And again what it has to do with the
"Resource oriented" concept? Am I missing something here?
Let me explain my position on Factory. I don't have any problems with
somebody implementing the Factory as a web service, I just don't see the
need for defining one in a standard. We have prototype Web Services
implemented in .NET, WebLogic, SunONE, and WebSphere and nowhere had to
worry about "factories" as Web Service access and instantiation is taken
care by the framework.
I think the mechanism of Web Service instantiation
should be left to framework providers, it's non of the business of Web
Service developer. The Web Service just have to be there for you when
accessing the port. As for ASAP specific information it can be easily passed
in the header (my "yes" vote) or as a predefined operation (my "no" vote).
I've been programming COM and EJB for years and was quite happy to see that
Web Services got rid of programmer-aware "factory" concept, so I don't need
to call coInitialize(Ex), coCreateInstance(Ex), etc. to get my COM interface
or to call EJBHome.create to get my EJBRemote. Why do we need to go back in
time and define factory for ASAP? Could you find "factory" as a principal
concept in any mainstream Web Services specification? I am not aware of
any...
Cheers,
Mike
-----Original Message-----
From: Keith Swenson [mailto:]
Sent: November 5, 2003 9:02 PM
To: Michael Shenfield; Mayilraj Krishnan; Jeffrey Ricker
Cc: ASAP
Subject: RE: [asap] Factory in ASAP
The factory concept is the central concept to this whole approach. Of
course, there are an infinite variety of ways that one might approach a
particular problem. This particular approach uses a small number of generic
"operations" on a large number of "resources". The meaning of the operation
depends on the address of the resource. This is the "Resource Oriented"
approach. The other approach is an "Operation Oriented" approach.
One should not be concerned about the multiplicity of the factories. The
existance of a factory does not mean that it takes up resources on the host
machine. The factory address can have data values encoded into it. I can,
if I wish, claim that I have 300 Million factories, one for each person in
the USA, by making the factory address have a SSN as a parameter (or any
other disambiguating value) in the address. I don't have to make 300
million records ahead of time. There is, then, no reason to try to reduce
the number of factories, nor is there any basis to equate a minimal number
of factories to a minimal feature set.
The WWW functions on this principle of a few operations on a large number of
addresses. For example, instead of using the web, you could define an
operation to retrieve the basic page, then an operation to retrieve each
graphic on the page, and another operation to retrieve the style sheet for
the page, etc. Some people would claim that this is a "good" way to design
the system because getting the style sheet you use an operation specifically
for getting the style sheet, and what you get back from this operation is
always a style sheet. Hence, it is strongly typed. Instead, the web merely
makes the page, the graphics, and the style sheet have different addresses.
The same GET operation can be used to get each one. Plus, I can remain
confident that if the future brings a new data type that can be embedded in
a page, the same GET operation can retrieve that data equally well. Some
people will complain that to display a page you need to make a number of GET
operations instead of one. True. Those same people might argue that a
single XYZ operation would be "simpler". This is NOT true, because the
specific information about the XYZ function must be specified some way in
order to get the basic linking accomplished. One problem, among many, is
that servers and browsers need to be upgraded simultaneously in order to get
new capabilities. Simultaneous upgrade does not happen in the real internet
world.
Back to ASAP: lets consider a real example. A car dealer has two
asynchronous web services: one that people can use to make an appointment at
the garage to get their car repaired, and the other to order a particular
accessory for a car. The reason I pick these examples is because they are
things that have a "duration" -- they persist over time. There should be no
disagreement that for a customer to arrange for a repair appointment some
data (expressed as XML) needs to be sent from the customer to the car
dealer, and that for ordering a accessory a different set of data needs to
be sent. This discussion then is really just over how to talk about how
these two pieces of data are different. Some approaches will make the
"operation name" be different between the two blocks of data. The ASAP
approach makes the "address" be different.
For this scenario, using an "Operation Oriented" approach, we could define
operations for CreateCarRepairAppointment, and CreateAccessoryOrder. We
would also need to define operations for CheckCarRepairAppointmentStatus,
CancelCarRepairAppointment, ChangeCarRepairAppointment,
CheckAccessoryOrderStatus, CancelAccessoryOrder, and ChangeAccessoryOrder.
The instance is automagically created behind the scenes, the correlation is
encoded somewhere in the data passed.
Using the "Resource Oriented" approach, we say there is an address for
"CarRepairAppointment" and a different address for the "AccessoryOrder".
Specifically, these are the addresses of the factory. Knowing these
addresses, we can call the generic CreateInstance operation. We get an
instance address which has the correlation information encoded into it. We
then can call the generic Cancel (actually Terminate), Check (actually Get),
and Change (actually Set) on the instance.
As you can see there is a one to one mapping between these two approaches.
The same number of actual messages is passed, the same amount of data must
be stored.
The reason for taking the "Resource Oriented" approach becomes more clear
when you carefully consider what must be done in order to link two systems
together. There are systems that are designed to be able to start remote
asynchronous processes. They already know about the basic operations:
Create, Get, Set, and Terminate. In order to link such a system to the
remote service, you must give it the information to link. Using the
resource oriented approach, you only need to give it the address of the
Factory resource. On the other hand, using the "Operation Oriented"
approach, you must first tell that system which operation is the create
operation. You have to program this somehow. You must tell it which
operation is to be used to cancel the remote service. Etc.
Once you buy into the basic idea that actual operation is a combination of
an address and a generic operation, there are some very cool things that can
be accomplished very easily: Imagine that company G build (through any
means) a system that automatically call the AccessoryOrder operations.
Company G is a trusted partner who brings a lot of business, so the car
dealer implements a "Pre Approved Accessory Order" that handles the order in
an expedited manner. Simply by changing the address of the factory, all the
associated operations are changed congruently, and the system interacts with
the expedited process.
For this discussion, I used a NamingConvention: CreateXXX, CheckXXXStatus,
ChangeXXX, and CancelXXX. This might be an alternative way to get the same
benefit. No such naming convention exists. The naming convention approach
gets really nasty when you want to encode something like a SSN into the
address. You would have 1,200,000,000 operations. We can easily
communicate addresses of a factory, but communicating the names of the
correct 4 operations from a field of 1.2 billion is somehow less
comfortable. Of course you could hide this by having 300M virtual WSDL
files (generating on demand of course so it does not take any space) but the
linking of operations is normally considered a design time activity. Most
systems to call remote processes are not really designed to take a WSDL file
at run time, search out the operation necessary according to a naming
convention, and then call that operation. It is messy if you want this kind
of flexibility. On the other hand, the "Resource Oriented" approach is
designed for exactly this kind of flexibility.
In summary, please think carefully about the "DYNAMICS" of linking systems
at run time as is necessary in a real life internet environment where change
is constant, and the systems you are linking to are not under your control.
-Keith
-----Original Message-----
From: Michael Shenfield [mailto:]
Sent: Wednesday, November 05, 2003 1:47 PM
To: Mayilraj Krishnan; Jeffrey Ricker
Cc: ASAP
Subject: RE: [asap] Factory in ASAP
I already expressed my concerns about "Factory" concept. In all existing Web
Services platforms that I am aware of the "Factory" is invisible for the WS
developer and non of her/his concern at the time of development and
deployment. I think we should step back and define a minimal scope of ASAP
(as agreed at the last two conference calls). I doubt "factory" should make
it there.
-----Original Message-----
From: Mayilraj Krishnan [mailto:]
Sent: November 5, 2003 3:32 PM
To: Jeffrey Ricker; ASAP
Subject: [asap] Factory in ASAP
So far I have been thinking we need just only one factory for ASAP
implementation or
the implementation of services could be conveniently placed under one
logical ASAP factory.
I have two web services one is check inventory, shipping. Why do I need to
create
two ASAP factory? I think the ASAP pattern is generic enough, it can just
have one factory.
[In terms of WSDL 1.2 we could map this to one ASAP (soap/transport
protocol) binding and one feature)]
Is that a right assumption?
Thanks
Mayilraj
At 11:35 AM 11/4/2003 -0500, Jeffrey Ricker wrote:
>I have attached files for describing the current draft of ASAP in WSDL.
>These are rough draft documents that have not been proofed.
>
>The asap.xsd describes the payloads
>The asap.wsdl is the basis for all ASAP services
>
>The concept here is to treat ASAP as a binding. The message structures
>are all the same, the programmer only has to define the ContextData and
>the ResultsData elements.
>
>The checkInventory.wsdl and productLevel.xsd files provide an example of
>this ASAP-as-a-binding approach.
>
>Ricker
>
>
>
>
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