The internet is based on a universally accepted set of protocols, HTTP, DNS, and TCP/IP, that provide the foundation for web-based cloud computing offerings. In this chapter we examine three critical web-based technologies at the next level of granularity that have been instrumental in improving the usability of web-based applications: Web services are used to request for and access infrastructure services in the cloud; AJAX-based user interfaces allow web-based applications to be user friendly; finally mashups bring a new dimension to software as a service by enabling users to compose multiple SaaS applications into a single user interface.

WEB SERVICES: SOAP AND REST

We have discussed the genesis and evolution of web services briefly in Chapter 2. Here we give a brief technical overview of both SOAP/WSDL and REST-based web services, and also compare these in the context of their utility in building cloud-based offerings. For a more detailed description of web services protocols, see [30].

SOAP/WSDL Web services

SOAP/WSDL web services evolved from the need to programmatically interconnect web-based applications. As a result SOAP/WSDL web services are essentially a form of remote procedure calls over HTTP, while also including support for nested structures (objects) in a manner similar to earlier extensions of RPC, such as CORBA; we shall return to this point later.

The elements of a SOAP/WSDL web service are illustrated in Figure 7.1, using as an example the service provided by Google for searching the web.