© 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 1 Product Design Alternative Generation, Evaluation, and Selection

© 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 2 Objectives  To list design alternative idea sources and generation techniques  To explain conventions and practices for stating requirements  To list and explain design alternative evaluation techniques  To present alternative selection techniques, particularly scoring matrices  To explain requirements prioritization

© 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 3 Topics  Product design resolution activities  Generating/improving alternatives  Stating design alternatives as requirements  Evaluating design alternatives  Selecting design alternatives

© 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4 Software Product Design Process

© 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 5 Generating Candidate Requirements  Common failing: too few alternatives  Idea sources Users and other stakeholders Props and metaphors Competitive products Similar products  Generation techniques Team brainstorming Individual brainstorming Modeling

© 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 6 Improving Candidate Requirements  Identify stakeholder need statements relevant to a candidate requirement.  Use the idea sources and techniques from the last slide to improve requirements.

© 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 7 Specification Notations  Natural language Easy to understand Prone to ambiguity and vagueness  Semi-formal notations More precise than natural language but not defined with mathematical rigor (most UML diagrams) More precise than natural language Easy to understand  Formal notations Mathematical and logical notations Very precise Hard to understand

© 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 8 Stating Requirements  Follow the rules of good technical writing. Write complete, simple sentences in the active voice. Define terms clearly and use them consistently. Etc.  Use “must” or “shall.”  Write verifiable requirements. There is a definitive procedure to determine whether the requirement is satisfied.

© 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 9 Requirements Atomization  Necessary for requirements traceability  Usually simple declarative sentences  Hierarchical numbering scheme  Number tables, diagrams, trees, etc. A requirement statement is atomic if it states a single product function, feature, characteristics, or property, and it has a unique identifier.

© 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 10 Product Design Principles  Adequacy—Designs that meet stakeholder needs, subject to constraints, are better.  Beauty—Beautiful design are better.  Economy—Design that can be built for less money, in less time, with less risk, are better.  Feasibility—A design is acceptable only if it can be realized.  Simplicity—Simpler designs are better.

© 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 11 Requirements Evaluation Techniques  With respect to design principles (heuristic evaluation)  By collecting data from stakeholders (empirical evaluation) Stakeholder surveys Usability studies  Users perform tasks on prototypes  Measurements used for comparison

© 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 12 Selecting Requirements Alternatives Selection among alternatives can be made by the following parties: Stakeholders only Designers only  Still based on stakeholder needs and desires Stakeholders and designers in collaboration  Participatory design

© 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 13 Selection Techniques 1  Pros and cons—List advantages and disadvantages and decide by vote or consensus Easy and fast Driven by persuasion  Crucial experiments—Decide based on the results of a survey or usability study Clear and objective results Slow and expensive Applies only when a single selection criterion is in question

© 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 14 Selection Techniques 2  Multi-dimensional ranking—assign criteria weights, score alternatives, and compare weighted sums Fairly objective Takes multiple criteria into account Fast and easy Difficult to use with many alternatives and criteria  Use the techniques most appropriate for the decision at hand.

© 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 15 Scoring Matrices  List alternatives as column headers  Determine the selection criteria and weights to be used  Add the selection criteria and weights as row headers  Rate each alternative with respect to each criterion, fill a cell  Fill in score cells by multiplying ratings by weights  Total the scores—high score wins

© 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 16 AquaLush Scoring Matrix Evaluation CriteriaMoisture ControlledTimer ControlledManually Controlled DescriptionWeightRatingScoreRatingScoreRatingScore Irrigation Control25% Reliability20% Ease of Use20% Robustness20% Risk15% Total Score

© 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 17 Prioritizing Requirements  Needed to make decisions about what to do first or what to leave out  Based on needs priorities, if available  Otherwise Designers can assign priorities based on needs Stakeholders can assign priorities  Stakeholder should always check priorities

© 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 18 Summary  Designers should use a variety of sources and techniques to generate many design alternatives.  Alternatives stated as requirements should be atomized, verifiable, use “must” or “shall” and be well written.  Alternatives can be evaluated heuristically or empirically  Designers or stakeholders can select design alternatives.  Several techniques can be used to select alternatives depending on the circumstances.