Abstract: Customer-focussed Selection and Prioritization of
common and variable Features with Quality Function Deployment
Andreas Helferich, Georg Herzwurm
Chair of Business Administration and Information Systems (Business Software)
Institute of Business Administration at Universität Stuttgart
Breitscheidstr. 2c
70174 Stuttgart
[helferich, herzwurm]@wi.uni-stuttgart.de
1 Introduction
The issue of software variability management can be addressed on an operational level,
addressing the question of how to manage the variability existing in the software product
families or product lines, but also on a strategic level, addressing the question of how to
decide where the members of a product line or family should differ. More specifically,
the strategic aspect comprises the following three questions:
•
Which products should be members of the product line?
•
What should be common to all members of the product line?
•
What should be the differences between members of the product line?
From a business point of view, the answer is quite easy in theory: there should be as
many different members of a product line as are necessary to satisfy the needs of the
customers in the market segment the company is planning to serve. The common “core“
consists of all features common to all members of the product line, the differences result
directly from the different needs of different customers in this market segment.
But also some of the more operational challenges in product line engineering can be
tackled using Software QFD: von der Maßen et al. identify challenges in the categories
Organization and Management, Requirements Engineering, Product- vs. platformspecific and Architecture (cf. [vdM+04, pp. 265ff.]). Some of these problems, most notably “high communication overhead”, “Discussions on design and not on requirements
level” and “No explicit prioritization of requirements” can easily be solved using Software QFD.
But how are the needs of the customers identified and translated into features? Quality
Function Deployment (QFD), a method developed in Japan, helps companies recognizing and satisfying customer needs. It has been successfully applied to develop or improve goods, services and software. Chapter 2 gives a brief description of QFD and
Software QFD, whereas Chapter 3 outlines the issues associated with using QFD for
product lines and a simple method how to deal with one of the issues. Finally, in chapter
4, topics for further research are identified.
2 Brief description of Quality Function Deployment
“QFD provides a systematic but more informal way of communication between customers and developers” ([Her+03], pg. 330) compared to traditional ways of formalizing and
specifying requirements. A project team consisting of customer representatives, developers/engineers and a moderator who is an expert in QFD works together during the
whole QFD process in order to assure that the final product’s features are not determined
by the technically possible but by the fitness for use, i.e. the features the customers demand. The software developers and/or engineers assure that the features can be implemented and that technological breakthrough innovations are not ignored.
QFD has been developed in the Japanese manufacturing industry (cf. [Akao90]), but can
easily be adapted towards software development if two differences are considered: first,
the software production process is basically a duplication process and implementation is
largely determined by the system design, especially the system architecture. Therefore,
the effort has to be directed mainly into the earlier stages. Secondly, “Software […] is
valued not for what it is, but for what it does” [Zult94]. Thus, the distinction between
product function and quality element has to be made (see table 1).
Table 1: Important definitions in Software QFD ([Her+03], pg. 331)
Figure 2 gives an overview of how customer requirements (voice of the customer table)
and product functions (voice of the engineer table) can be combined and prioritized and
integrated into the software development process. This approach has been used to develop the Calendar function in SAP R/3© (cf. [Her+00]) as well as for electronic and
mobile business systems (cf. [Her+02]).
Figure 1: Herzwurm’s and Schockert’S PriFo Software QFD model ([Her+00], pg.
87)
3 Using Quality Function Deployment for Software Product Lines
Upper class
product
Specificationss
high
Lower class
product
The most important difference between the “usual” use of QFD and the use for Product
Lines (no matter if they are Software Product Lines or not) is that usually one product is
developed instead of a set of related products. This results in having different target
values for certain features (these features indicate variation points). One simple way to
cope with this is having not a single row of target values but multiple rows, as illustrated
in figure 2. This could either be one row of target values for each product or one row for
each class of products. In the second case, the values for high and low would indicate the
upper and lower border and the value for mid would indicate a solution that’s somewhere
around the middle of the upper and lower border. This has been used by Hoffmann and
Berger for a “exposer” product family in a German company from the printing sector (cf.
[HoBe00]), but can easily be adapted for software product lines. The final paper/presentation would present an example for the use in a simple software product line.
high
mid
low
mid
low
Figure 2: extension of the House of Quality to accommodate product lines
4 Need for further research
The method presented here to represent different members of a product line can still be
improved: while it is very helpful in its identifying features helping to satisfy customer
needs and prioritizing these features, its ability to handle large numbers of product line
members and variations in a feature is limited since it easily gets rather complex. Additionally, neither the integration with existing methods to model features and variation
points nor the effect that differences between customers or customer groups have on the
advantages of one variation of a feature over another are as yet solved. But since QFD is
a very flexible method, it is likely that a clever series of matrices will solve these problems. For example, we have identified a way to integrate QFD and Object Oriented
modelling (cf. [Her+04]). Building on this and the method presented here, we think a
way to link customer groups and appropriate product line members will be found, same
should be true for integrating QFD and modelling and implementing variability.
Bibliography
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