• Promote a better understanding of service definitions
• Agree the expected content of a service definition
• Decide how to publish the expected content e.g. as a set of requirements.

Introduction

Service definitions (and other service related artefacts) are defined in the SWIM reference glossary. 

It is important to disambiguate the terms as they share some commonalities in purpose and scope. It is possible to represent the commonalities and differences as follows:

in order to use a service

consider using a service

initial evaluation of the information service characteristics

Note: Service overviews "promote service discovery" according to the definition. However, this ability is not confined to service overviews. The SWIM Registry promotes service discovery.

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.

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.

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.

Content of a service definition

Service Definitions - minimum content

Informative diagrams

The diagram below illustrates how a community of interest produces a service definition for use by multiple service providers in their implementations. It uses the steps of the Service Orientation process.

Note: the technical choices can come in the service definition. Deviations should be within the bandwidth of the definition - if it is precise on technical choices, implementers have fewer technical choices and so degree of harmonisation will be higher.

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