(1) What type of faults can occur in Ajax applications that do not occur in
other types of web applications? What techniques can be used to detect these
Ajax specific faults?

Ans. The two common type of faults that can occur in  Ajax Web applications
than in other kinds of applications, the faults associated with the
following features:
  i. Asynchronous messages and
  ii.DOM manipulation
        Due to asynchronous messages Ajax programmers cannot make the
assumption that each server response comes immediately after the request,
with nothing occurring in-between. When the network performance degrades, we
may observe unintended interleaving of server messages, swapped callbacks
etc.
        DOM manipulation, for example deriving from assumptions about the
DOM structure which become invalid during the execution because of page
manipulation by Javascript code or an inconsistency between code and DOM,
which makes the code reference an incorrect or nonexistent part of the DOM,
causes executions occurring under incorrect DOM state.
  As described in the slides, an FSM is used to detect the specific faults.

(2) Describe briefly Ajax architecture. Show how asynchronous messages help
improving user experience in a typical Ajax application.

Ans. Ajax (Asynchronous Javascript And XML) is a group
of technologies having 
i.   HTML and CSS for information presentation.
ii.  The Document Object Model to access and modify the displayed
information.
iii. The XMLHttpRequest object to retrieve data from the web server
asynchronously.
iv.  XML to wrap data
v.   Javascript code to bind everything together.
        The Ajax object XMLHttpRequest wraps any service request or data
travelling between client and server. The asynchronous response from the
server is handled at the client side by Javascript code which is part of a
callback triggered by the response. Upon arrival of the server message, the
handler method associated with such an event is run. Depending on
the received data, the message handler can change the structure or content
of the current web page through the DOM. The main technological novelty of
Ajax is the asynchronous communication between client and server, combined
with the reflection mechanism provided by the DOM, which allows updating
parts of the current Web page without resending the entire page.
        The synchronous request-response protocol used by traditional Web
applications introduces a delay between one page and the next one, which
prevents all interactions requiring a short response time. On the contrary,
Ajax applications are based on asynchronous requests, which leave the user
interface active and responsive.

(3) What is the importance of semantically interacting events?

Ans. When the result of two events executed together is different than
executed in isolation, the two events are semantically interacting. We can
use this relationship for test case reduction. By considering only
semantically interacting events, we expect not to loose too much in terms of
fault revealing capability of the test suite, since we are retaining all
paths involving semantic interactions between events.