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									   Pharos University in Alexandria                       Distributed Systems

   Faculty of Engineering                                Course code : CE353

   Fifth Year Students                                   Lecturer: Prof.Dr. Saleh El-Shehaby

   Computer Engineering                                  TA: Eng. Nora Samir

Web Services:

  A web service is typically an application programming interface (API) or Web API
that is accessed via Hypertext Transfer Protocol (HTTP) and executed on a remote
system, hosting the requested service. Web services tend to fall into one of two
camps: big web services and Restful web services.

The W3C defines a "web service" as "a software system designed to support
interoperable machine-to-machine interaction over a network. It has an interface
described in a machine-process able format (specifically Web Services Description
Language WSDL). Other systems interact with the web service in a manner
prescribed by its description using SOAP messages, typically conveyed using HTTP
with an XML serialization in conjunction with other Web-related standards."

The W3C also states, "We can identify two major classes of Web services, REST-
compliant Web services, in which the primary purpose of the service is to
manipulate XML representations of Web resources using a uniform set of "stateless"
operations; and arbitrary Web services, in which the service may expose an
arbitrary set of operations."
Cloud Computer:
Cloud computing is Internet-based computing, whereby shared servers provide resources,
software, and data to computers and other devices on demand, as with the electricity grid.
Cloud computing is a natural evolution of the widespread adoption of virtualization,
service-oriented architecture and utility computing. Details are abstracted from
consumers, who no longer have need for expertise in, or control over, the technology
infrastructure "in the cloud" that supports them.

Cloud computing describes a new supplement, consumption, and delivery model for IT
services based on the Internet, and it typically involves over-the-Internet provision of
dynamically scalable and often virtualized resources. It is a byproduct and consequence of
the ease-of-access to remote computing sites provided by the Internet. This frequently
takes the form of web-based tools or applications that users can access and use through a
web browser as if it were a program installed locally on their own computer.

The National Institute of Standards and Technology (NIST) provide a somewhat more
objective and specific definition here. The term "cloud" is used as a metaphor for the
Internet, based on the cloud drawing used in the past to represent the telephone network,
and later to depict the Internet in computer network diagrams as an abstraction of the
underlying infrastructure it represents. Typical cloud computing providers deliver
common business applications online that are accessed from another Web service or
software like a Web browser, while the software and data are stored on servers.

Most cloud computing infrastructures consist of services delivered through common
centers and built on servers. Clouds often appear as single points of access for consumers'
computing needs. Commercial offerings are generally expected to meet quality of service
(QoS) requirements of customers, and typically include service level agreements (SLAs).
The major cloud service providers include Amazon, Rackspace Cloud, Salesforce, Skytap,
Microsoft and Google. Some of the larger IT firms that are actively involved in cloud
computing are Fujitsu, Dell, Red Hat, Hewlett Packard, IBM VMware, and NetApp.
Ajax shorthand for Asynchronous JavaScript and XML) is a group of interrelated web
development methods used on the client-side to create interactive web applications. With
Ajax, web applications can retrieve data from the server asynchronously in the background
without interfering with the display and behavior of the existing page. Data is usually
retrieved using the XMLHttpRequest object. Despite the name, the use of XML is not needed,
and the requests need not be asynchronous.

Like DHTML and LAMP, Ajax is not one technology, but a group of technologies. Ajax uses a
combination of HTML and CSS to mark up and style information. The DOM is accessed with
JavaScript to dynamically display, and to allow the user to interact with, the information
presented. JavaScript and the XMLHttpRequest object provide a method for exchanging
data asynchronously between browser and server to avoid full page reloads.

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