What is excatly the technology stack defining Web APIs?

Question

What are the abstract levels of technology that are used to build a Web APIs such as GData?

Answer 1

Web services typically use one of two technologies.

So called REST APIs make use of the HTTP GET,PUT, DELETE etc to create a web service. For instance a search engine could give an API where you search for by doing an HTTP GET request from www.searchengine.apple which returns all results for apple. The technology building blocks are the existing basic web protocols that you are familiar with, HTTP, HTML, and server side, PHP, ASP etc.

Alternately you can use SOAP and WSDL to define an XML based API based around defined requests which can take a number of parameters, which will return a response. Many languages can import the WSDL file for a service and provide a functional API based on it. This makes accessing the service very easy.

For more reading on WSDL and SOAP I recommend www.w3cschools.com

There are pros and cons of both methods which I will leave you to explore.

Regards

Answer 2

It's worth mentioning that GDATA itself is largely the Atom Publishing Protocol (RFC 5023) + extensions (as allowed by the spec),and with a proprietary authentication method.

So, that's an abstraction over REST that adds semantics for publishing and editing a collection of objects.