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

Browser
UI
HTTP
GET
HTML
Server
App
Server
Figure 1.3 Classical web client/server interaction pattern.
As the web matured, more server-side scripting languages appeared, examples
of which include PHP, Python, Ruby, JavaServer Pages (JSP), and Active
Server Pages (ASP). Such languages typically run on the server, have access to
various resources, and are capable of creating and returning web pages upon
request.
The ability to generate web pages contributed to the separation of concerns
(presentation, business logic, data) and realization of multi-tier architectures
for web applications.
1.1.3 Web Architecture
By the year 2000, many of the initial concepts forming the backbone of the web
(e.g., HTTP, URI, HTML) and additional recommendations such as Cascading
Style Sheets (CSS) (level 2) and Document Object Model (DOM) (W3C, a)
(level 2) were standardized through the World Wide Web Consortium (W3C).
In addition, an architectural style of the web called REpresentational State
Transfer (REST) was proposed by Fielding (2000), capturing the essence of
the main features of the web architecture, through architectural constraints
and properties. Rest specifies a layered client-stateless-server architecture in
which each request is independent of the previous ones, inducing the property
of scalability. In practice, however, not many web implementations can
be found that abide by the restrictions set by Rest. In particular, many developers
have ignored the stateless constraint by allowing the server to keep track
of relevant state changes. Chapter 2 discusses the architecture of the web in
more detail.
1.1.4 Rich Internet Applications
It soon became apparent that HTML was not designed for creating an interactive
Graphical User Interface (GUI). Classical web applications are, inherently,
based on a multi-page user interface model, in which interactions are based on
a synchronous page-sequence paradigm. While simple and elegant in design
for exchanging documents, this model has many limitations for developing
modern web applications with user friendly human-computer interaction.
The main limitations can be summarized as follows:
• Low lever of user interactivity;
4 1.1. Web Evolution