BS ISO IEC 26550:2015 pdf free download – Software and systemsengineering – Referencemodel for product lineengineering and management
4 From single-system engineering and management toward product lineengineering and management
Single-system engineering and management is the dominant way of conceptualizing and developingsoftware and systems products. This Clause first outlines some of the main challenges software andsystems product companies face in using single-system engineering and management approaches. Itidentifies variability management as the most challenging area.Variability management is discussedin 4.1. The clause concludes by explaining major differences between single-system engineering andmanagement and product line engineering and management.Understanding these differences is a keyfor successful organizational transitioning from single-system engineering and management towardproduct line engineering and management.
4.1 Challenges product companies face in the use of single-system engineering andmanagement
The excessive use of single-system engineering and management in environments where theassumptions no longer hold contributes to a variety of issues encountered by customers,end-users,and providers. For example, customers may feel their needs are unique and acquire and sustainexpensive tailored systems while commoditized, inexpensive products might be completely adequate.End-users may experience that the functionality they really need is difficult to find and/or use becausethe software systems are too complex and provide too much functionality.Finally, a provider may sellseveral interrelated products, which look and feel completely different and do not interoperate, even tothe same customers.
Providers of single products typically encounter at least some of the following issues when usingsingle-system engineering: work efforts and costs are underestimated, productivity is overestimated,must-have features are missing, product schedules and/or quality goals are not met, and/or customersatisfaction remains lower than expected. Work efforts may be underestimated and productivityoverestimated because the organization has never before created a similar product or if it has, theorganizational unit who created the similar product may not want to share its experiences and otherpossibly reusable assets due to rivalry between organizational units. Inaccurate estimates togetherwith typically fixed budgets result in schedule fluctuations,missing features, and/or quality issues.Quality issues may also result from the lack of a reuse culture because the software developed fromscratch typically has much higher defect density than the software reusing well-tested components.
The accommodation of adequate variability is typically the most significant problem faced bythe providers of single products. In this context, the variability needs typically emerge over timefrom interactions with various customers. Providers commonly use one or more seemingly simplebut ineffective tactics to deal with emerging variability.For example, a provider may incorporatevariability into a single product by introducing more and more (partly end-user-visible) parameters inthe product and more and more if-then-else-statements in the source code text of the product to dealwith the parameters during run time.As a result, the number of source code lines grows, the sourcecode becomes increasingly complex to understand and maintain, and the testability (and often alsothe performance) of the software deteriorates.Alternatively, a provider with an existing product maydeal with the variable requirements of a new customer by branching a new product from the existingproduct, modifying the source code of the new product, merging the modified source code back to themain line when there is time and other resources available, and finally deleting the branch. Branchingand merging is very expensive and error prone and the source code of the main line will typically becomevery complex after a few branches and merges,requiring expensive periodical refactoring to utilizethe tactic on a long term basis.In the worst case, the provider may end up with many partially cloned products and no main line of source code to maintain. Such ineffective tactics for managing variabilityalso make the jobs of software developers tedious and are likely to increase employee turnover.