Web services are a type of internet software that use standardized messaging protocols and are made available from an application service provider’s web server for use by a client or other web-based programs.
Web services can range from major services such as storage management or customer relationship management down to much more limited services such as the furnishing of a stock quote or the checking of bids for an auction item. The term is sometimes also referred to as application services.
Modern day business applications use variety of programming platforms to develop web-based applications. Some applications may be developed in Java, others in .Net, while some other in Angular JS, Node.js, etc.
Most often than not, these heterogeneous applications need some sort of communication to happen between them. Since they are built using different development languages, it becomes really difficult to ensure accurate communication between applications.
API is a broader term than web service. It describes a communication layer between all types of systems, transmitting data both via web and offline channels. For instance, such APIs as DirectX or Vulkan are operating system interfaces that don’t use the web to exchange information.
A web service is an API that operates only via web communication. So, we can say that all web services are APIs; however not all APIs are necessarily web services. In this article, we may use both API and web service terms implying that we are talking about web-based APIs.
SOAP stands for Simple Object Access Protocol. It is a standardized protocol for message exchange between web applications. The message format supported by SOAP is XML. A web service that is based on SOAP protocol is called SOAP web service.
REST stands for Representational State Transfer. It is an architectural style that describes some constraints for web service development. The web services satisfying these constraints are RESTful web services.