What is the difference between a webservice and an API? Is the difference more than the protocol used to transfer data? thanks.
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Check this http://en.wikipedia.org/wiki/Web_service
As the link mentioned then Web API is a development in Web services that most likely relates to Web 2.0, whereas SOAP based services are replaced by REST based communications. Note that REST services do not require XML, SOAP, or WSDL service-API definitions so this is major different to traditional web service.
Basically, a webservice is a method of communication between two machines while an API is an exposed layer allowing you to program against something.
You could very well have an API and the main method of interacting with that API is via a webservice.
The technical definitions (courtesy of Wikipedia) are:
An application programming interface (API) is a set of routines, data structures, object classes and/or protocols provided by libraries and/or operating system services in order to support the building of applications.
A Web service (also Web Service) is defined by the W3C as "a software system designed to support interoperable machine-to-machine interaction over a network"
API is code based integration while web service is message based integration with interoperable standards having a contract such as WSDL.
API's are a published interface which defines how component A communicates with component B.
For example, Doubleclick have a published Java API which allows users to interrogate the database tables to get information about their online advertising campaign.
e.g. call GetNumberClicks (user name)
To implement the API, you have to add the Doubleclick .jar file to your class path. The call is local.
A web service is a form of API where the interface is defined by means of a WSDL. This allows remote calling of an interface over HTTP.
If Doubleclick implemented their interface as a web service, they would use something like Axis2 running inside Tomcat.
The remote user would call the web service
e.g. call GetNumberClicksWebService (user name)
and the GetNumberClicksWebService service would call GetNumberClicks locally.
another example: google map api vs google direction api web service, while the former serves (delivers) javascript file to the site (which can then be used as an api to make new functions) , the later is a Rest web service delivering data (in json or xml format), which can be processed (but not used in an api sense).
Think of Web service as a web api. API is such a general term now so a web service is an interface to functionality, usually business related, that you can get to from the network over a variety of protocols.
API(Application Programming Interface), the full form itself suggests that its an Interface which allows you to program for your application with the help or support of some other Application's Interface which exposes some sort of functionality which is useful to your application.
E.g showing updated currency exchange rates on your website would need some third party Interface to program against unless you plan to have your own database with currency rates and regular updates to the same. This set of functionality is when already available with some one else and when they want to share it with others they have to have an endpoint to communicate with the others who are interested in such interactions so they deploy it on web by the means of web-services. This end point is nothing but interface of their application which you can program against hence API.
In a generic sense an webservice IS a API over HTTP. They often utilize JSON or XML, but there are some other approaches as well.
Source: Stackoverflow.com