On 18-May-05, at 2:50 PM, Hamid Ben Malek wrote:
<snip/>
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.
It doesn't matter how many services there are. What matters is that the architecture is service oriented. That means a single service and a single consumer would technically be service oriented.
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).
Why should I care about call sequence in SOA-RM's context?
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.
Not true. I'm sure there is a way to distinguish OO from SO, but this is not it. A service developer has to be just as aware of the ecosystem that his service is deploying to as much as the object developer does.
Apache doesn't need to have a conference call with me every week because my developers are using Xalan, an OO component.
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.
Not true either. I can change Xalan on my JBoss installation with reinstalling my application.
SO is OO, basically, with some value-add infrastructure such as discovery and description.
-Matt