Re: [soa-rm] What is SOA (Really???)

["Gregory A. Kohring" <kohring@ccrl-nece.de>]

<quote>
Make an example of something that is not conformant to the SOA RM and
explain why.
</quote>


One of the problems we are having in this respect is
generalizing from the wrong basis model. Or more to the point,
have we reached agreement upon what basis model SOA is generalizing
from?

In my opinion, SOA RM generalizes Client-Server; whereby
the "client" is generalized to "consumer" and the "server" is
generalized to "service". (In this sense, SOA is a fundamental model
and we should try to keep it simple.)

Seen from this viewpoint, we should ask what is the difference
between client and consumer, server and service and the relationship
between the respective pairs.

A "client" has the server's description hard-wired. The policy,
contract, data model and processing model are all hard coded into both
the client and the server.

A "consumer" on the other hand has some goal to achieve and must
first discover a service which can achieve this goal, understand
the service's policy and contract to see if the service's policy is
in alignment with its own policy and constraints, examine the
processing model to determine whether a session needs to be
established before the request can be submitted and examine the
data model to determine what format is needed for the input data;
only then can the consumer submit a request to the service.

If you accept this scenario (which I know is a big "IF" ;-), then
an example of something which is Client-Server, but not SOA is
FTP.  With FTP the policy (username-password authentication),
contract (list of allowed commands), data model (byte order of the
ftp packet) and processing model (control channel, data channel)
are all hard-coded in both the client and the server, there is no room
for dynamic inspection and negotiation.

In my opinion, it is this inflexibility which forms the main
demarcation between the Client-Server model and the SOA model.


-- Greg




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G.A. Kohring
C&C Research Laboratories, NEC Europe Ltd.
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