How exactly do web services work

Web services: services from machine to machine

A web service is addressed via a unique Uniform Resource Identifier (URI). Similar to a Uniform Resource Locator (URL) that can be used to address websites, the URI is an address for the corresponding web service. In theory, that also plays Directory service UDDI a role through which web services can be found. However, this service never caught on and the biggest supporters withdrew from the project.

However, the Web Service Description Language (WSDL) is more important: A web service has one File in WSDL, in which the service is described in more detail. The information enables the client to understand what functions it can perform on the server via the web service. After all, communication works via various protocols and architectures. Popular are z. B. the network protocol SOAP in combination with the Internet standard HTTP or RESTful web services. These techniques are used to send requests and responses back and forth.

Often the communication works with the Extensible Markup Language (XML). The relatively simple language can be understood by people and computers alike and is ideally suited to connecting systems with different requirements. But REST also allows other formats such as JSON.

A web service example to illustrate this: Let us assume that software was written in Visual Basic and runs on a Windows machine. The program requires the service of an Apache web server. To do this, the client sends a SOAP request in the form of an HTTP message to the server. The web service interprets the content of the request and ensures that the server takes an action. After execution, the web service formulates a response and sends it back to the client - again with SOAP and HTTP. There the answer is interpreted again and the information reaches the software, where it is further processed.