» Introduction.

» What Does AJAX Stand For ?

• Asynchronous
• Javascript
• And
• XML

» What Does All This Mean ?

• AJAX can be used to build rich and dynamic web interfaces.
• Using AJAX, web pages can communicate with their host server 'behind the scenes'.
• Data is returned to the browser asynchronously as an XML text stream.

» XML Is Returned to the Browser.

• The XML that is returned to the browser can be parsed into a DOM tree.
• The XML DOM tree can be processed on the browser using javascript.
• Javascript can then be used to update or modify the browser display, as appropriate.

» A Key Feature of AJAX.

• This process is driven by client-side scripting.
• The user does not need to refresh a page or 'post' a form for the display to be updated.
• Javascript can be used to manipulate the browser's display - changing content, style, positioning etc.

» What Can AJAX be Used For ?

• Applications can range from small 'message widgets' embedded in a web page, to ...
• Full-blown web-based application user interface frameworks.
• Like many powerful new techniques, it is sometimes used inappropriately.

» Do All Browsers Support AJAX ?

• Most modern browsers now support both asynchronous xml and javascript.
• There are differences in the asynchronous communication components across browsers.
• We use javascript 'wrappers' to hide these, and present client apps with a uniform API.

» What Is Needed on the Server-Side ?

• The server just needs to be able to respond to an http/https request with a stream of xml text.
  - Web servers are good at doing this !
• The XML is requested and returned to the client browser using standard http/https.
• A call can include 'arguments' for the business logic that generates the XML response.

» Some Difficulties With AJAX.

• The design of good asynchronous user interfaces is not straightforward.
• Working with javascript can be problematic and error prone in complex applications.
• Inappropriate use of AJAX and/or design/coding errors can lead to heavy network traffic and server loading.

» Security: Secrecy and Authentication.

• Secrecy. Text that is sent using http can easily be intercepted and read.
  - https transport can be used if required.
• Authentication. We want to be sure who a remote client really is.
  - Cryptographic techniques based on a 'shared secret' can be used, with protection against 'replay' attacks.

» Where We Use AJAX Techniques.

• We use AJAX to provide richer front-ends to products such as the
  Stibium Naming Server.
• Our web site also uses AJAX, for example to support our Site Map Explorer.