To describe services seem almost intangible and very hard in practice considering so many is struggling with it. Although, i think it is still possible to apply som structure to the concept without making too hard on yourself. When applying a bit of structure it can be easier to move forward afterwards. I often hear examples of what an IT service might be and there is always references to a description that should clearly state what is included and not included in a service. What it should be and examples of it is harder to find.
If we want to define a service I would assume that it has more than one part. Among those parts there might be some that would be considered as mandatory versus some which could be optional. If we just for the fun of it called these parts service functions. Then we could start from this service function and ask ourself, one by one, what is it for? How is it used? what does it provide? If we have the ability too answer the question, i think that we have a pretty good idea of who the consumer is and how the consumers process looks like when the consumer is actually using our service function. An important point is that we need to understand what parts of the consumer process is our IT service enabling?
I could go even further and say that the service is nothing/empty until one or more service functions are defined. This would mean that we actually define the service through service functions in this case. If a corresponding service function does not exist the service does not cover it. This gives us our first structure.
Next we want to group the services. I would guess that there are more customers and consumers that can benefit from a service the more standard the service is. So we should try to group our service in service groups. Lets continue this example with an IT department and a business department/unit trying to define the services for this business unit. One way of grouping the services could be that the business unit is one service group and all services that are specific for and used by this business unit are grouped into one service group. If there are more units working with similar areas and consuming same services it could be beneficiary to add them all to the same group and choose a good name for the group that corresponds to the business the units are performing. This way it is easy to have a discussion about cost, delivery, availability etc. because everything or a majority is applicable for the business unit you are communicating with. The business unit is also consuming more standard services like messaging, communication and service desk. These can be grouped into a service group called shared services or corporate service. The result of this is that a customer will probably consume services from multiple service groups where one will be very close to their core business and the other tend to be more standard services.
That would give us the following picture:
Here you se two service groups with services and service functions. This way it is possible to structure the content of a service with service functions and to group the services in customer segments or service groups even if all consumers are internally in one enterprise or externally.