Visualizing non-functional requirements
Neil A. Ernst, Yijun Yu, and John Mylopoulos
Department of Computer Science
University of Toronto, Toronto, Canada
{nernst,yijun,jm}@cs.utoronto.ca
Abstract
Information systems can be visualized with many tools.
Typically these tools present functional artifacts from
various phases of the development life-cycle; these in-
clude requirements models, architecture and design di-
agrams, and implementation code. The syntactic struc-
tures of these artifacts are often presented in a textual
language using symbols, or a graphical one using nodes
and edges. In this paper, we propose a quality-based vi-
sualization scheme. Such a scheme is layered on top of
these functional artifacts for presenting non-functional
aspects of the system. To do this, we use quantified qual-
ity attributes. As an example, we visualize the quality
attributes of trust and performance among various non-
functional requirements of information systems.
Keywords quality attributes visualization, non-
functional requirements, tradeoffs, performance, trust
1. Introduction
Software visualization supports various phases of
the development lifecycle. For example, goal-oriented
software requirements techniques result in goal struc-
tures like those presented in Objectiver for the
KAOS approach [6] and OpenOME for the i*/Tropos
approach [25]; documented software designs are dis-
played as UML diagrams in various UML editors,
such as Rational Software Architect ; re-
verse engineered software architectures are shown as
boxes and arrows in visualization tools like Creole
and lsedit ; the implemented software source code
is syntax-highlighted in all modern text editors, such as
VIM , Emacs , and Eclipse ; and scattered, cross-
cutting concerns are plotted as aspects in the AspectJ
visualizer.
These visualizations focus on the functional arti-
facts of a software system, ranging from abstract arti-
facts such as requirement goals to very concrete ones
that are part of an actual software implementation. As
the software artifacts get more detailed, their represen-
tations become more complex, making it harder for a
viewer to be aware of quality issues – such as maintain-
ability, reusability, security, and trust – without losing
focus of primary functional concerns.
Some measures are commonly used for reducing
the perceived complexity in visualizations, thereby al-
lowing users to divert attention to wider issues. Many
of these are an attempt to implement Shneiderman’s
visual information seeking mantra – “overview first,
zoom and filter, then details-on-demand” [1]. These
include scrolling, zooming, the use of color, and vari-
ous information abstraction mechanisms such as nest-
ing and folding.
These treatments of artifacts do not, however, re-
veal the tradeoffs among different non-functional as-
pects of the software systems [17]. They present the
complexity or size of the system. With regard to the
qualities of the software product, such as performance,
security, usability, and trust, we need to classify the ex-
isting functional artifacts to reflect their quantified rep-
resentation of quality attributes. This requires a metric
for each such attribute that can be attached to the func-
tional artifact (whether it is a goal, UML element, or
source code). Priorities of such quality concerns can
also be highlighted to reveal bottlenecks.
In this paper, we generalize the idea used in visual-
izing a single dimension of concern (performance) to
multiple dimensions. We show how visual variables
such as color, size, shape, and thickness can be as-
sociated with different quantified dimensions. These
quality-based visual clues are presented together with
the functional artifacts. This helps the human decision
maker to assess tradeoffs of quality attributes on the pri-
mary functional concern.
The remainder of the paper is organized as follows.
Section 2 presents a visual formalism to allow multiple
quality concerns to be compared. Section 3 expands this
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