Comparison Four Distributed Architecture Alternatives for SOA

To finally understand what a SOA is, it is interesting to understand what it is not. Therefore a brief delimitation from differing architecture alternatives is given.

1. Client Server:
The client-server approach is one of the best established architectures for distributed computing. The approach and the technology available are mature and stable. Systems of this type can be easily implemented and optimized for special application scenarios. On the other hand, once a client-server system is established it is difficult to change the functionality of the system. Therefore its flexibility is limited and best used, if the business process is expected to be stable and changes are seldom

2. J2EE: Java Enterprise Edition (J2EE)
J2EE is also a mature technology and widely used for distributed computing in object-oriented worlds. Objects are typically smaller than services in a SOA and they are more closely intertwined with each other. The technology is independent from the operating system, but of course, not from the programming language. Objects can be inserted, modified or replaced without stopping and restarting the whole system, so J2EE increases the flexibility for adapting business processes compared to client-server systems. The expected reuse factor in a J2EE environment is as high as expected in a SOA. One main difference between objects of a J2EE architecture and services of a SOA is, that distributed objects lack an explicit contract – they only define an interface. rom the conceptual point of view objects are passive and can be used from any other object. Objects don’t commit their functionality to other objects like services do. It is possible to implement a SOA with J2EE

3. P2P (Peer to peer)
In a true peer-to-peer (P2P) architecture every participant is independent and equal. Central components or services which are used by all other participants should not exist. Every participant provides services to and also consumes services from others. The whole infrastructure is very dynamic and self-organizing, which leads to a high level of flexibility but on the other hand reliability can not be granted. The technology behind peer-to-peer networks is relatively young and mainly used in the field of sharing scenarios. In practice most peer-to-peer architectures use some central components like index servers or registries for better performance but with the disadvantage of providing single points of failure. Without using central services it is very difficult to find resources needed in a suitable amount of time. P2P networks are well suited for highly dynamic environments (see

4. Multi Agent Systems:
Multi agent systems typically consist of many individual units, so called agents. The most important properties of an agent are that it is autonomous, aware of its environment and pro-active. The system infrastructure provides the communication technology for all agents in the system. These provide and consume services, which can be regulated through contracts, so it could be possible that an agent has to pay for some services other agents provide. On the other hand agents commit the services they can provide and define the level of quality. A major difference between agents and services is that the former can ‘decide on their own’ – agents are meant for behaving like human beings. Therefore it is also possible that agents behave opportunistic, meaning that they possibly try to cheat others. Multi agent systems can be regarded as a mixture of peer-to-peer architectures and SOA, but because of the complexity of the infrastructure required, they seem to be seldom suited for huge internet applications or B2B-integration