【正文】 ed architecture presents an approach for building distributed systems that deliver application functionality as services to either enduser applications or other services. It is prised of elements that can be categorized into functional and quality of service. A closer look at serviceoriented architecture ? Functional aspects include: ? Transport is the mechanism used to move service requests from the service consumer to the service provider, and service responses from the service provider to the service consumer. ? Service Communication Protocol is an agreed mechanism that the service provider and the service consumer use to municate what is being requested and what is being returned. ? Service Description is an agreed schema for describing what the service is, how it should be invoked, and what data is required to invoke the service successfully. ? Service describes an actual service that is made available for use. ? Business Process is a collection of services, invoked in a particular sequence with a particular set of rules, to meet a business requirement. Note that a business process could be considered a service in its own right, which leads to the idea that business processes may be posed of services of different granularities. ? The Service Registry is a repository of service and data descriptions which may be used by service providers to publish their services, and service consumers to discover or find available services. The service registry may provide other functions to services that require a centralized repository. A closer look at serviceoriented architecture ? Quality of service aspects include: ? Policy is a set of conditions or rules under which a service provider makes the service available to consumers. There are aspects of policy which are functional, and aspects which relate to quality of service。這使得構(gòu)建在各種各樣的系統(tǒng)中的服務(wù)可以以一種統(tǒng)一和通用的方式進(jìn)行交互。接口是采用中立的方式進(jìn)行定義的，它應(yīng)該獨(dú)立于實(shí)現(xiàn)服務(wù)的硬件平臺、操作系統(tǒng)和編程語言。 therefore we have the policy function in both functional and quality of service areas. ? Security is the set of rules that might be applied to the identification, authorization, and access control of service consumers invoking services. ? Transaction is the set of attributes that might be applied to a group of services to deliver a consistent result. For example, if a group of three services are to be used to plete a business function, all must plete or none must plete. ? Management is the set of attributes that might be applied to managing the services provided or consumed. SOA collaborations ? The following figure shows the collaborations in a serviceoriented architecture. The collaborations follows the “find, bind and invoke” paradigm. ? A service consumer performs dynamic service location by querying the service registry for a service that matches its criteria. ? If the service exists, the registry provides the consumer with the interface contract and the endpoint address for the service. SOA collaborations ? The roles in a serviceoriented architecture are: ? Service consumer: The service consumer is an application, a software module or another service that requires a service. It initiates the enquiry of the service in the registry, binds to the service over a transport, and executes the service function. The service consumer executes the service according to the interface contract. ? Service provider: The service provider is a workaddressable entity that accepts and executes requests from consumers. It publishes its services and interface contract to the service registry so that the service consumer can discover and access the service. ? Service registry: A service registry is the enabler for service discovery. It contains a repository of available services and allows for the lookup of service provider interfaces to interested service consumers. ? Each entity in the serviceoriented architecture can play one (or more) of the three roles of service provider, consumer and registry. SOA collaborations ? The operations in a serviceoriented architecture are: ? Publish: To be accessible, a service description must be published so that it can be discovered and invoked by a service consumer. ? Find: A service requestor locates a service by querying the service registry for a service that meets its criteria. ? Bind and invoke: After retrieving the service description, the service consumer proceeds to invoke the service according to the information in the service description. ? The artifacts in a serviceoriented architecture are: ? Service: A service that is made available for use through a published interface that allows it to be invoked by the service consumer. ? Service description: A service description specifies the way a service consumer will interact with the service provider. It specifies the format of the request and response from the service. This description may specify a set of preconditions, post conditions and/or quality of service (QoS) levels. SOA collaborations ? In addition to dynamic service discovery and definition of a service interface contract, a serviceoriented architecture has the following characteristics: ? Services are selfcontained and modular. ? Services support interoperability. ? Services are loosely coupled. ? Services are locationtransparent. ? Services are posite modules, prised of ponents. ? These characteristics are also central to fulfilling the requirements for an ebusiness on demand? operational environment. ? Finally, serviceoriented architecture is not a new notion. Services vs. ponents ? A service is a coarsegrained processing unit that consumes and produces sets of objects passedbyvalue. ? It is not the same as an object in programming language terms. Instead, it is perhaps closer to the concept of