Service composition combines services together to achieve a certain goal. This procedure is used to create new functionality when a single atomic service cannot satisfy user requirements.
Services taking part in a SOA can be combined together to create a new service for achieving a certain goal. There are several different usages for service composition:
- Service orchestration: Business processes can be implemented by orchestrating existing business functions implemented as services. Such functionality is exposed as a service that can be used in other business processes.
- Service choreography: Describes the service interactions from a global point of view. They are often used to describe the public processes of different business partners, in contrast to service orchestrations which describe the executable private process of each single partner.
- Service coordination: Services follow a coordination protocol driven by a central coordinator in order to perform a distributed activity. For example, an auction scenario, where the actions of sellers and bidders and the outcome of the auction are driven by a auctioneer.
- Service assembly: Models define how different services should be packaged together into a deployable software solution. Some of these composition model types can often be combined together. For example, after creating a service choreography model, it can be refined to service orchestrations for each partner.
The lifecycle of a composed service includes four phases: synthesis, execution, monitoring, and adaptation.
