Analysis and Testing of Ajax-based Single-page Web Applications

To the best of our knowledge, at the time of writing no study had been
conducted to explore the actual tradeoffs in terms of data coherence, server
performance and scalability, network performance, and data delivery reliability,
involved in applying a push- versus pull-based approach to web-based
settings.
Web applications are distributed systems, and distributed systems are inherently
more difficult to engineer (Wang et al., 2005) and test than sequential
systems (Alager and Venkatsean, 1993). Controllability, observability (Chen
et al., 2006), and reproducibility are all challenging issues in distributed testing
environments. In order to conduct a comparison of different web data
delivery techniques, first an automated, controllable, and repeatable test environment
has to be set up, to obtain accurate empirical data for each approach.
This leads us to our next research question:
Research Question 3.1
What are the tradeoffs of applying pull- and push-based data delivery
techniques on the web? Can we set up an automated distributed test
environment to obtain empirical data for comparison?
Automatic Crawling
General web search engines, such as Google and Yahoo!, cover only a portion
of the web called the publicly indexable web, which consists of the set of web
pages reachable purely by following hyperlinks. Dynamic content behind
web forms and client-side scripting is generally ignored and referred to as the
hidden web (Raghavan and Garcia-Molina, 2001).
Although there has been extensive research on finding and exposing the
hidden web behind forms (Barbosa and Freire, 2007; de Carvalho and Silva,
2004; Lage et al., 2004; Ntoulas et al., 2005; Raghavan and Garcia-Molina,
2001; Madhavan et al., 2008), the hidden web induced as a result of client-side
scripting in general and Ajax in particular has gained very little attention so
far.
Consequently, while Ajax techniques are very promising in terms of improving
rich interactivity and responsiveness, Ajax-based applications may
very well end up in the hidden web. We believe this is one of the main reasons
people hesitate to use Ajax on their public web sites.
Crawling Ajax-based web interfaces is fundamentally more challenging
than crawling classical multi-page applications. The main reason is that in
the classical web model, all states are explicit, and each one corresponds to a
unique URL. In Ajax-based applications, however, the state of the user interface
is determined dynamically, through event-driven changes in the run-time
DOM-tree. This means that simply extracting and following hyperlinks does
not suffice any longer. New methods and techniques are required to dynamically
analyze the complex user interface elements, events, and state changes,
which leads us to our next question:
Chapter 1. Introduction 17