Saturday, September 15, 2012

SOA, Separation of concerns and agnosticism (1/5)

Middleware and Separation of Concerns

Middleware can exist in many ways but most common approach is either the application service or the ESB approach. Regardless of what platform or technology the middleware is hosted on, the main  purpose of the middleware layer is the same: separation of concerns.

As an example the following picture shows that the middleware decouples the consumer from the back end systems by providing services that act on behalf of the back end. This way the consumer does not need to be concerned with the back end, and the back end does not need to be concerned with who the consumer is or how it works.

Decoupling should be explained a bit further. Two systems are coupled if there is a dependency between the two. What we try to achieve with decoupling is that we try to minimize the amount of dependencies between them.

Separation of concerns can be observed in middleware in many ways but starting with offering services on the middleware platform allows us to wrap back end systems. This then allows us to offer a standardized way of accessing underlying back end systems. Standardizing the access to logic can improve interoperability. To provide increased opportunity of interoperability, we need to understand that we have to standardize contracts. If two systems are interoperable it means that they can easily exchange information, or in other words, cooperate. If we put in lots of effort we might be able to provide a system that has something called intrinsic interoperability.

Intrinsic interoperability is achieved if we have standardized a system in such a way (and if we have built logic in such a way that the interoperability can be supported) that if two systems exchange messages, the messages can be easily understood, without the need for (complex) transformations or translations.

For intrinsic interoperability to be achieved, a number of prerequisites must be met, and even then matters are not easy and require significant amount of attention in the governance area.

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