Web Services

Web Services

Web Services refers to the technologies that allow for making connections. It is standardized medium to propagate communication between the client and server applications on the World Wide Web. It provide a common platform that allows multiple applications built on various programming languages to have the ability to communicate with each other

 Services

are what you connect together using Web Services. It is the endpoint of a connection. Also, a service has some type of underlying computer system that supports the connection offered. The combination of services—internal and external to an organization—make up a service-oriented architecture.

• Web Services Description Language (WSDL)
• Web Services Dynamic Discovery (WS-Discovery)
• Web Services Endpoint Language (WSEL)
• Web Services Metadata Exchange (WS-MetaDataExchange)
• Web Services Policy Framework (WS-Policy)

Application Program Interfaces (APIs)

The concept of an application program interface (API)  was used in the 1988 POSIX defintion for compatibility among variants of Unix and other operating systems. CORBA and DCOM both used the concept starting in the 1980s.
It is related to informaton hiding from software engineering that goes back to at least the early 1980s:

The term "hiding" implies that effective modularity can be achieved by defining a set of independentmodules that communicate with one another only that information that is necessary to achieve software function.

APIs/information hiding allow for the creation of a minimal interface that is relatively stable that can be used by other software systems to access or manipulate the underlying systems or data. This allows for enhancements to the underlying systems or data without disturbing the software systems that use the API.

 

Service-oriented architecture( SOA )

A service-oriented architecture is essentially a collection of services. These services communicate with each other which involves either simple data passing or it could involve two or more services coordinating some activity. Some means of connecting services to each other is needed.
Service-oriented architectures are not a new thing. The first service-oriented architecture for many people in the past was with the use DCOM or Object Request Brokers (ORBs) based on the CORBA specification. For more on DCOM and CORBA, see Prior Service-Oriented Architectures.
 The following figure illustrates a basic service-oriented architecture. It shows a service consumer at the right sending a service request message to a service provider at the left.  The request and subsequent response connections are defined in some way that is understandable to both the service consumer and service provider.

Web Services Specifications

Three specifications for Web Services are illustrated in this section: SOAP, REST, and JSON.

A]  SOAP

SOAP was originally part of the specification that included  (WSDL) and (UDDI). It is used now without WSDL and UDDI. Instead of the discovery process described in the History of the Web Services Specification section below, SOAP messages are hard-coded or genereated without the use of a repository. The interaction is illustrated in the figure below.

B] Representation State Transfer (REST)

Representation State Transfer (REST) appeals to developers because it has a simpler style that makes it easier to use than SOAP. It also less verbose so that less volume is sent when communicating.

C] JavaScript Object Notation (JSON)

While both SOAP and REST use XML for interchange, JavaScript Object Notation (JSON) uses a subset of JavaScript.

When to Use SOAP, REST, JSON or Other Options

There really is no "best" option for Web Services. Generally, you will use whatever your service provider supports. If you use multiple service providers, it is easily possible that you will be using all three Web Services specifications: SOAP, REST, and JSON.

Web Services Description Language (WSDL)

The  WSDL forms the basis for the original Web Services specification.
The steps involved in providing and consuming a service are:

1. A service provider describes its service using WSDL. This definition is published to a repository of services. The repository could use Universal Description, Discovery, and Integration (UDDI). Other forms of directories could also be used.
2. A service consumer issues one or more queries to the repository to locate a service and determine how to communicate with that service. 
3. Part of the WSDL provided by the service provider is passed to the service consumer. This tells the service consumer what the requests and responses are for the service provider.
4. The service consumer uses the WSDL to send a request to the service provider.
5. The service provider provides the expected response to the service consumer.

UDDI registry : can be searched in various ways to obtain contact information and the Web Services available for various organizations. How much "discovery" was ever used is open to discussion. Nevertheless, even without the discovery portion, the UDDI registry is a way to keep up-to-date on the Web Services your organization currently uses. It can be used at design time and with governance.
An alternative to UDDI :  ebXML Registry



Reference: https://www.service-architecture.com