Purpose and usage
The purpose of a service definition is to harmonize service implementations.
A service definition is produced by a community of interest. It contains a set of service metadata that defines a type of service.
For example, a service definition may define an AMAN service.
However, the service definition does not provide every piece of metadata about resulting service instances. For example, some service definitions will be technology agnostic and say nothing about the technologies to be used when implementing the service. The metadata is collected throughout the Service Orientation process. Much of it is collected by the end of the design step. This may also include recommendations for some technical aspects e.g. exchange model or a particular binding.
A service definition may be registered in the SWIM Registry. This will allow it to be discovered by service providers.
A service definition is used by service providers. The service instance they implement is a running service that conforms to the service definition. A service provider will produce a service description that completes the service metadata, expanding on that that was available in the service definition. The service description refers to the service definition ("standard") that was used as the basis for the service instance (see SWIM-SERV-010 Service standard reference).
Creation
Bottom-up, top-down, middle-out
The service orientation process is written with a classical top-down approach e.g. starting with operational needs and the identification of a new service if this has not already performed.
A list of identified services is available at https://www.eatmportal.eu/working/rnd/service-overview.
However, it acknowledges that much of the activities can occur based on existing services that are in need of alignment. A service definition can therefore be the result of a community coming together to align a service that its members have already implemented.
It is, of course, also possible to start the service orientation process somewhere in the middle and develop the justification for the services at the same time as implementing it.
Legacy to new
A service definition can be used as a part of the service lifecycle process to support the transition from a legacy service or system to the SWIM environment. The legacy service can be "abstracted" into a service definition that ensures the same requirements are carried forward into the new service as it is implemented and deployed.
Minimum content of service definitions
Interpreting the content
The diagram below gives the minimum content to be included in a service definition by the issuing community of interest.
The content is to be used by the different service providers. In that regards, the service definition places requirements on the service provider. The goal is for a set of harmonised service instances that conform to the service definition by implementing its requirements.
The more restrictive the service definition is, the fewer choices an implementer has and so the degree of harmonisation will be higher.
Requirement SWIM-SERV-120 - Service standard reference in the EUROCONTROL SWIM Service Description Specification, requires that the deviations and additions to the referenced service definition are listed. This makes it clear to service consumers when the service definition has not been followed.
