Service (systems architecture)
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In the context of Enterprise architecture, Service-orientation, and Service-oriented architecture, the term service refers to a set of related software functionality, together with the policies that should control their usage.
OASIS (organization) defines service as "a mechanism to enable access to one or more capabilities, where the access is provided using a prescribed interface and is exercised consistent with constraints and policies as specified by the service description." 
An Enterprise Architecture Team will develop the organization’s “Service” model first by defining the top level Business Functions. Once the Business Functions are defined they are decomposed into “Services” which represent the processes and activities needed to manage the assets of the organization in their various states. An example here would be the decomposition of the Business Function “Manage Orders” into “Services” such as “Create Order”, “Fulfill Order”, “Ship Order”, “Invoice Order”, “Cancel/Update Order”, etc.
Service Description / Specification
A “Service” has a description or specification. This description consists of:
- An explicit and detailed narrative definition supported by a low (but not detailed [not implementation specific]) level process model. The narrative definition is in some cases augmented by machine-readable semantic information about the service which facilitates service mediation and consistency checking of an Enterprise Architecture.
- A set of performance indicators that address measures/performance parameters such as availability (when should members of the organization be able to perform the function), duration (how long should it take to perform the function), rate (how often will the function be performed over a period of time), etc.
- A linkage to the organization’s information model showing what information the “Service” owns (creates, reads, updates, and deletes) and which information it references and is owned by other “Services”.
A Web service provides one way of implementing the automated aspects of a given business or technical service.
Telecommunication network architectures, such as IMS, are able to provide subscribers with various Next Generation Network Services.