Web service - Wikipedia
Port types define a set of operations supported by the Web service. Service bindings The following figure shows the relationship of the basic parts of WSDL . The term web service is either. (generic) a service offered by an electronic device to another REST-compliant web services, in which the primary purpose of the service is to manipulate XML representations of web resources . "Web Services Architecture § Relationship to the World Wide Web and REST Architectures". An WSDL document describes a web service. It specifies the location of the service, and the methods of the service, using these major elements.
Rules for communication between different systems need to be defined, such as: How one system can request data from another system. Which specific parameters are needed in the data request. What would be the structure of the data produced. What error messages to display when a certain rule for communication is not observed, to make troubleshooting easier. Proposals for Autonomous Web Services AWS seek to develop more flexible web services which do not rely on strict rules.
Once the software system finds out which other system it should contact, it would then contact that system using a special protocol called SOAP Simple Object Access Protocol.
The service provider system would first validate the data request by referring to the WSDL file, and then process the request and send the data under the SOAP protocol.
Automated design methods[ edit ] Web services in a service-oriented architecture.
Automated tools can aid in the creation of a web service. Even more so than in n-tier environments, application designers need to appreciate fully how the introduction of services will affect existing data and business models, especially if current or future EAI initiatives need to comply to a service-oriented model.
As the utilization of services diversifies, the significance of security and scalability requirements are amplified. Well-designed service-oriented environments will attempt to address these challenges with adequate infrastructure, rather than custom, application-specific solutions. For detailed information about service-oriented architecture design principles, and how SOAs can lead to the evolution of a service-oriented enterprise, see Chapter The service-oriented architecture introduces a new logical layer within the distributed computing platform.
The service integration layer establishes a common point of integration within application tiers and across application boundaries. The roles and scenarios illustrated in the next two sections are limited to the involvement of Web services only.
The underlying SOAP messaging framework is explained separately, later in this chapter. Depending on the context with which it's viewed, as well as the state of the currently running task, the same Web service can change roles or be assigned multiple roles at the same time. Service provider When acting as a service provider, a Web service exposes a public interface through which it can be invoked by requestors of the service.
Web Services Components
A service provider promotes this interface by publishing a service description. In a client-server model, the service provider is comparable to the server Figure 3. The term "service provider" can also be used to describe the organization or environment hosting providing the Web service. A service provider can also act as a service requestor. For example, a Web service can play the role of service provider when a service requestor asks it to perform a function.
It can then act as a service requestor when it later contacts the original service requestor now acting as a service provider to ask for status information.
Service requestor A service requestor is the sender of a Web service message or the software program requesting a specific Web service. Service requestors are sometimes referred to as service consumers. A service requestor can also be a service provider. For instance, in a request and response pattern, the initiating Web service first acts as a service requestor when initially requesting information from the service provider.
The same Web service then plays the role of a service provider when responding to the original request. Intermediary The role of intermediary is assumed by the Web service when it receives a message from a service requestor, and then forwards the message to a service provider. Intermediaries can exist in many different forms. Some are passive, and simply relay or route messages, whereas others actively process a message before passing it on.
Typically, intermediaries are allowed only to process and modify the message header. To preserve the integrity of a message, its data should not be altered. Intermediaries are discussed in more detail in Chapter 9.
By definition, a web service is any piece of software that makes itself available over the Internet and standardizes its communication via XML encoding. A client invokes a web service by sending a request usually in the form of an XML messageand the service sends back an XML response. Web services invoke communication over a network, with HTTP as the most common means of connectivity between the two systems. Above image visually describes the difference between an API and a web service.
Introduction to Web Services Technologies: SOA, SOAP, WSDL and UDDI
Why is a web API not a web service? When HTTP is used to abstract systems from one another, the systems are considered to be more loosely coupled when compared to web services and therefore the entire system is considered less brittle. What is an API? In contrast, an API specifies how software components should interact with each other.