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

components. The architectures have a well defined protocol for small interactions
among known client/server components. Data needed to be transferred
over the network is significantly reduced. This can result in faster response
data transfers. Their architecture takes advantage of client side processing
resulting in improved user interactivity, smaller number of round-trips, and a
reduced web server load.
The architectural decisions behind these frameworks change the way we
develop web applications. Instead of thinking in terms of sequences of Web
pages, Web developers can now program their applications in the more intuitive
(single page) component- and event-based fashion along the lines of,
e.g., AWT and Swing.
2.3 Architectural Styles
In this section, we first introduce the architectural terminology used in this
chapter and explore whether styles and principles as developed in the software
architecture research community, and specifically those related to network-based
environments, can be of help in formalizing the architectural properties
of Ajax applications.
2.3.1 Terminology
In this chapter we use the software architectural concepts and terminology
as used by Fielding (Fielding, 2000) which in turn is based on the work of
Perry and Wolf (Perry and Wolf, 1992). Thus, a software architecture is defined
(Perry and Wolf, 1992) as a configuration of architectural elements —
processing, connectors, and data — constrained in their relationships in order
to achieve a desired set of architectural properties.
An architectural style, in turn, (Fielding, 2000) is a coordinated set of architectural
constraints that restricts the roles of architectural elements and the
allowed relationships among those elements within any architecture that conforms
to that style. An architectural style constrains both the design elements
and the relationships among them (Perry and Wolf, 1992) in such a way as
to result in software systems with certain desired properties. Clements et al.
(Clements et al., 2002) define an architectural style as a specialization of element
and relation types, together with a set of constraints on how they can be
used. A style can also be seen as an abstraction of recurring composition and
interaction characteristics in a set of architectures.
An architectural system can be composed of multiple styles and a style
can be a hybrid of other styles (Shaw and Garlan, 1996). Styles can be seen
as reusable (Monroe and Garlan, 1996) common architectural patterns within
different system architectures and hence the term architectural pattern is also
used to describe the same concept (Bass et al., 2003).
The benefits of using styles can be summarized as follows:
• Design reuse: well-understood solutions applied to new problems
30 2.3. Architectural Styles