RE: [soa-rm] SOA System

[Hamid Ben Malek <HMalek@us.fujitsu.com>]

As Object-Orientation is about constructing applications from building blocks called "objects", Service-Orientation is about constructing applications from building blocks called "Services".

              

Question: Is it necessary that there be more than one service in order that SOA be SOA?

Answer: One SOA service by itself does not do much. A set of SOA services is called an “SOA System”. When we say “SOA”, we generally assume the existence of an SOA system which is the subject of discourse.

 

Question: Is it necessary to call services only in sequence?

Answer: Yes and No. In fact, the question stated like this does not make sense. There are two cases. The first case is when the initial caller is a simple service consumer (that is a client which is not an SOA service). The second case is where the caller is an SOA service. For the first case, the client makes calls in a sequence only. However, that does not mean that the messages will be delivered in that sequence. All the messages go through the SOA Fabric and they may arrive in different order or at the same time. For the second case where the caller is an SOA service, there is a possibility of calling in parallel (instead of in sequence). In fact, an SOA service may even initiate a complex process which consists of a mixture of parallel and sequential calls (For example, initiating a BPM process whose activities are the SOA services within an SOA system).

 

[Duane]: My gut feeling is that having multiple services is probably a given for any specific implementation of SOA, however it is not a requirements for something to be service oriented.  If I architect one application and build it with a single service, service description, policy set, (+ whateverElseGetsInTheReferenceModel), is that service oriented architecture?  I think yes.

 

There are two phases: the development phase and then the deployment phase. During the development phase, each service can be developed by a team somewhere on the planet: “Service A” being developed by a team in China, “Service B” being developed by a team in Canada, “Service C” being developed by a team in Japan, etc…  When the development phase is done, the various services are deployed to form an SOA system. SOA only becomes SOA when the deployment phase starts. A single service by itself is not SOA. Two important things to notice about this process:

 

1.    Independence of Services: One of the biggest differences between Object-Orientation and Service-Orientation is the fact that Service-Orientation allows various services to be built independently of each other. This is not possible with Object-Orientation where the various developers need to communicate during the creation of the various objects.

2.    Incremental Deployment: This is the second big difference between Object-Orientation and Service-Orientation. In object orientation, an application must be deployed as a whole (as one single unit). In service orientation, an application is always deployed incrementally. Various services are added at various times without breaking the functionality of the whole system.

 

Regards,

 

Hamid.

 

 

-----Original Message-----
From: Duane Nickull [mailto:dnickull@adobe.com]
Sent: Wednesday, May 18, 2005 11:06 AM
Cc: SOA-RM
Subject: Re: [soa-rm] FYI: BEA SOA Reference Diagram

 

 

 

Ken Laskey wrote:

 

> The essence of a SOA is multiple services coming together to satisfy a

> set of needs.

 

This is the core point we have not reached consensus on yet.  This is a

well worded as can be so I would like to use this assertion as a basis

for the discussion.

 

Thoughts:

 

I would agree that "The essence of a SOA infrastructure is multiple

services coming together to satisfy a set of needs.  I do have

reservations about the concept of multiplicity of services being used as

a key metric to define SOA.

 

Questions:    

1. Is it necessary that there be more than one service in order that SOA

be SOA?

2. If yes to #1, is it necessary to call services only in sequence?

 

My gut feeling is that having multiple services is probably a given for

any specific implementation of SOA, however it is not a requirements for

something to be service oriented.  If I architect one application and

build it with a single service, service description, policy set, (+

whateverElseGetsInTheReferenceModel), is that service oriented

architecture?  I think yes.

 

I would fully support a reference architecture depicting multiple

services  being used either sequentially or in parallel, however think

that is a sub project best left for a dedicated sub committee.

 

Duane

 

>