Make it explicit
An appropriate approach to address at least parts of this issue is to conduct a KANO analysis where engineers will define features all customers would expect, but also excitement features that may surprise the users in a positive way. Take the iPhone as an example: Expected features include the ability to make phone calls, to maintain a contact list, or to send SMS messages. If a product lacks one of these, customers will be disappointed, but even the coverage of all expected features won't make a customer excited. Excitement features of the iPhone include the Touch Screen and the possibility to add functionality using apps. It is important to mention that today's excitement features will become expected features in the future. Obviously, developers of a mobile phone need to know the expected features in order to prevent any disappointment. However, in many cases these expected features are only known implicitly which works fine if you are familiar with the problem domain, but leads to trouble if this is not the case. Thus, the first conclusion is to make these requirements explicit. The introduction of a problem domain model and of a feature tree prove to be excellent ways to understand the domain and the features as well as their dependence and interaction.
So far I mentioned functional aspects, but implicit assumptions about quality attributes should not be neglected either. Suppose, it would take minutes to find a person in the contact list or to initiate a phone call. Such cross-cutting concerns may not appear in the requirements specification, but nonetheless are essential for successful development. Thus, also the quality attributes must be made explicit which does not only turn out to be important for design but also for the establishment of a test strategy and test plans.
Besides requirements the business strategy and business case often make implicit assumptions such as the kinds of users or market segments or features or future evolution. Whenever architects are not informed about these assumptions, they can neither check their feasibility or validity nor can they provide the right solution. How could someone provide a solution for a vaguely understood problem anyway? Conclusion: always make sure that you obtain sufficient information from management. And mind the ambiguity problem! For instance, I once asked several product managers about their usability requirement. It turned out that every single one of them had a completely different understanding of usability. This is the reason, why a common model and effective communication are so important.
Another problem area is the mapping from the problem domain to the solution domain. Developers may use particular technologies, because they find these the right ones for addressing the problem. Or managers may prescribe technologies without knowing their implications. Architects may enforce decisions without giving a rationale. And developers may make implicit but wrong assumptions about the architecture.Thus, making decisions based on explicit assumptions is inevitable for successful design. For example, architects and developers should verify assumptions and document decisions explicitly. If you don't believe this, think about gifts you gave other persons based on your assumptions.
A benefit of explicit information is that it can be cross-checked and allows traceability. In a development project all the groups of stakeholders should not consider themselves as disconnected islands. Instead, they should share knowledge by using effective communication strategies. Also, they should make their decision process and decisions transparent to the other groups. Basically, it is like having one common information repository where stakeholders may have different views. But these different views must map consistently to each other. This is the reason why architects are the right persons to enforce making everything explicit. In particular, the development of platforms and product lines is very sensitive to implicit information, because failure to consider this information has an impact on many applications.
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