Informatics 121 Software Design I Lecture 5 Duplication of course material for any commercial purpose without the explicit written permission of the professor is prohibited.

Today’s lecture Design failures Practice

Intermezzo: what experts do Experts prefer solutions that they know work Experts look around Experts take inspiration from wherever they can Experts use analogy Experts use design methods (selectively) Experts network

Two fundamental challenges The nature of software The nature of people

Nature of software (Brooks) Complexity software is among the most complex people-made artifacts Conformity software has no laws of nature that simplify its existence; rather, it lives in a world of designed artifacts to which it much conform Changeability software is subject to continuous pressure to change Invisibility because the reality of software is not embedded into space, it is inherently unvisualizable

Nature of people Diversity Indiscernibility Familiarity Volatility people differ in how they experience the world Indiscernibility experiences are distinctly mental in nature, with tangible reactions and signs not always matching their actual experience Familiarity people tend to be risk averse, sticking to role, organizational, and societal norms and values Volatility with every new exposure, people reinterpret and modify their opinions and expectations

Software design is a wicked problem The problem is not understood until after the formulation of a solution Wicked problems have no stopping rule Solutions to wicked problems are not right or wrong Every wicked problem is essentially novel and unique Every solution to a wicked problem is a “one shot operation” Wicked problems have no given alternative solutions Worse, software design is a ‘hard’ wicked problem

Seven difficulties every software designer faces Prediction Tradeoffs Change Bias Longevity Quality, cost, and effort Source code as a design notation

Difficulty #1: predicting people’s experiences Software design is a predictive activity that must anticipate the experiences of people account for differing experiences account for shifting experiences Furthermore, when people share their vision for a future change in the world, they tend to be conservative The difficulty lies in how to balance what people perceive they need and what they actually need

Difficulty #2: tradeoffs Tradeoffs must be made continuously over the course of a design project a design solution is judged relative to other possible solutions that could have been made it is frequently impossible to quantify the relative virtues of each alternative Furthermore, any given design solution inevitably satisfies certain stakeholders more than others The difficulty lies in how to balance the decisions across the needs and experiences of the various stakeholders

Difficulty #3: change Change happens and must be accommodated changing client demands changing context of people, hardware, and software changing understanding of the design problem changing attitudes of the audience Furthermore, the more complete a design solution already is, the more difficult it will be to change it The difficulty lies in how to balance accommodating change with making sufficient progress on the design solution

Difficulty #4: bias Bias exists within all stakeholders, and can be a positive or negative influence audience designer client others Furthermore, bias is typically difficult to detect and address The challenge lies in how to balance benefiting from positive bias while avoiding the effects of negative bias

Difficulty #5: longevity Longevity is expected of most software design solutions software does not wear out software fulfills critical societal services Furthermore, it very likely will need to accommodate new needs as well as deviations from present needs The difficulty lies in how to balance addressing today’s design problem with accommodating future, unknown needs

Difficulty #6: quality, cost, and effort Quality, cost, and effort are three constraining factors in design, not all of which can be optimized at the same time cost constraints typically set by other stakeholders cost constraints typically set before the design project is truly understood Furthermore, there is no stopping rule, since no optimal design solution exists The difficulty lies in how to balance a design solution that is of good enough quality with expectations on cost and effort

Difficulty #7: source code as a design notation Source code is a terrible design notation for expressing goals, constraints, assumptions, decisions, and ideas Furthermore, other software design notations typically do not map easily to source code while they certainly help make progress, much manual effort remains in transforming findings stemming from the use of these notations to the source code The difficulty lies in how to balance use of other design notations with the need to ultimately express the design solution in source code

Practice Virtual campus visit Disney electronic queue management system Mountain climbing 3D guide system Social restaurant table

Disney electronic queue management system