As described in sections “Participation
in a SOA Ecosystem view” and “Realization
of a SOA Ecosystem view”, there are several types of contracts in the
SOA ecosystem. From the management perspective, three basic types of the
contracts relate to:
·
relationship between service
provider and consumer;
·
communication with the service;
·
control of the quality of the
service execution.
Before a service is invoked the first time, SOA ecosystem assumes that the
consumer gets into agreement with the service provider about the service
features and characteristics that will be provided by the service and available
to the consumer; this contract is known as a service contract:
a service contract is an
implicit or an explicit and documented agreement between the service consumer
and service provider about the use of the service based on the commitment
by a service provider to provide service functionality and
results, and realize real world effects as well as on the commitment
by a service consumer to interact with the service in the
manner described in the service description.
In some situations, a consumer may be allowed to use a service
description as an implicit default service contract; in other situations, the
service description may be set as a mandatory service contract, e.g. for
security services. In the case of business services, it is anticipated that the
service contract is explicit and the agreement between business consumer and
business service provider is formalized. So, an implicit service contract is an agreement on the consumer side with the terms, conditions, features and interaction means specified in the service description "as is" that do not require any priory interactions between the service consumer and the service provider. An explicit service contract alway requires a form of up-front interaction between the service consumer and the service provider regarding the choice or selection of the subset of of the elements of the service description that would be applicable to the interaction with the service and affect related joint action. The examples of the explicit service contracts are: 1) a consumer can choose which one of the offered policy alternatives or interface alternatives the consumer wants to use in the service interaction; 2) a consumer wants to use only a subset of the business functionality offered by the service and pay a prorate cost for this.