fredag 10 maj 2013

Service vs System

In my mind a system is never a service and a service is never a system. They might even have the same name but they are definitely not the same thing for me. Let me explain myself. Below in the picture you se system X. System X has 2 applications, a web server, one database and four servers. Together all this could be called a system.
Is this the same as saying that this could be described as a service? well lets expand the example with yet another system that has basically the same complexity but delivers different application functionality. Then we get the following.

The above picture shows us two systems with applications, databases and web servers installed on servers. not a to uncommon situation.
So let us try to apply a service to the picture. To identify a service we need to understand "what" the user is doing. lets say that the user is registering an order, so the first part of the service we are creating is the "order registration" service function. We use the service function to define the service and the service will have many service functions. Our first service function is defined and now we can identify what parts from the systems that need to be available so the user is able to register and order.

to register an order we need the following parts of the infrastructure.
- application 1 (from system X)
- web server 1 (from system X)
- db 1 (from system X)
- db 2 (from system Y)
It would look like this if our function is included in the picture and indicated in yellow.
As you can figure out there is a connection between system X and system Y which obviously is required for registration of an order. this is not shown any way between the systems. it is only shown in correlation with the service function. This means that "what" the user "does" and how this is realized in an IT solution is key for how we would define a service and its service functions.

In real life, the solutions are far more complex and the interaction between systems are very common without that the user realizes it. This strengthens the fact that a system and service is not, nor will ever be, the same thing.

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