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Informatics 121 Software Design I
Lecture 2 Duplication of course material for any commercial purpose without the explicit written permission of the professor is prohibited.
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Discussion There will be discussion this Friday
Please join your designated discussion Note new classroom: SE2 1304
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Intermezzo: what experts do
Experts prefer simple solutions Experts solve simpler problems first Experts divide and conquer Experts do not overgeneralize Experts design elegant abstractions Experts use metaphor
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Today Defining design Feasibility and desirability
Four types of design Design cycle
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Three themes Design focuses on identifying a novel envisioned future
Design involves deliberate decision making and planning; it is not simply acting out of impulse Design decisions are consequential: there are stakeholders who must be satisfied with the result
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Our definition To decide upon a plan for a novel change in the world that, when realized, satisfies stakeholders But as we did so opportunistically, we quickly figured out we needed something to frame the discussion, what are they doing when they are doing this? So we arrived at design behaviors – things they do, things that recur, and things that have a definite purpose in the design meeting with respect to advancing the design at hand.
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Design designer plan maker change in the world other stakeholders
audience experiences
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Design a luxury airplane
designer plan maker change in the world other stakeholders audience experiences
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Design a library designer plan maker change in the world
other stakeholders audience experiences
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Design an award designer plan maker change in the world
other stakeholders audience experiences
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Design fields Architecture design Graphic design Fashion design
Game design Chip design Car design Urban design Product design Interior design …
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Design fields Architecture design Graphic design Fashion design
Game design Chip design Car design Urban design Product design Interior design … Writing Painting Sculpting Music composition …
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Design fields Architecture design Graphic design Fashion design
Game design Chip design Car design Urban design Product design Interior design … Writing Painting Sculpting Music composition … Software design
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Design designer plan maker change in the world other stakeholders
audience experiences
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Software design software designer source code compiler*
runnable program other stakeholders users experiences [* or, at times, the person who installs and configures the software instead of the compiler]
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Feasibility and desirability
designer plan maker change in the world other stakeholders audience experiences
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Feasibility and desirability
designer plan maker change in the world other stakeholders audience experiences desirability
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Four types of design desirability feasibility
what is it to accomplish? how does one interact with it? desirability feasibility what is its conceptual core? what are its implementation details?
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Four types of design what is it to accomplish? satisfactory experience
how does one interact with it? satisfactory experience plan for realization change in the world what is its conceptual core? what are its implementation details?
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Four types of software design
what is it to accomplish? how does one interact with it? application design satisfactory experience plan for realization interaction design change in the world what is its conceptual core? what are its implementation details? architecture design implementation design
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Design an instant message system
what is it to accomplish? how does one interact with it? application design satisfactory experience plan for realization interaction design change in the world what is its conceptual core? what are its implementation details? architecture design implementation design
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Design a word processor
what is it to accomplish? how does one interact with it? application design satisfactory experience plan for realization interaction design change in the world what is its conceptual core? what are its implementation details? architecture design implementation design
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Design problem and solution
design solution
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Design project design problem design solution design project
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Design cycle synthesize analyze evaluate
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Design cycle goals constraints assumptions decisions ideas synthesize
analyze evaluate
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Goals A goal represents an explicit acknowledgment of a desired result that the eventual design solution must achieve Goals may be suggested by any of the stakeholders client other stakeholders audience designer Goals change over time, and may or may not be (partially) addressed by the current state of the design solution
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Example goals The luxury airplane must be 10% more fuel-efficient than its predecessor The library must be able to hold 250,000 books The award must be representative of the professional society that is commissioning it
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Constraints A constraint represents an explicit acknowledgment of a condition that restricts the design project Constraints may be suggested by any of the stakeholders client other stakeholders audience designer Constraints change over time, and may or may not be (partially) met by the current state of the design project
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Example constraints The luxury airplane must weigh less than 50,000 pounds The library must not violate federal disability laws The award must cost less than $1000 to produce
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Assumptions An assumption represents a fact that is taken for granted, may or may not be true, and influences the design project Assumptions may be made by any of the stakeholders client other stakeholders audience designer Assumptions change over time, and may or may not be (partially) fulfilled by the current state of the design project
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Example assumptions The average person weighs 85 kilograms
The library needs to serve the community with an area stocked with personal computers The professional society’s logo is red and white, which therefore must be its preferred colors for the award
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Decisions A decision represents a specific choice of how to further the design solution, typically after some amount of consideration Decisions are the sole responsibility of the designer, though they can be (heavily) influenced by other stakeholders Decisions change over time, and new decisions may or may not (partially) align with the current state of the design project
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Example decisions The fuselage and wings of the luxury airplane shall be made out of carbon composites The library shall have bookshelves that are not movable The award shall be made out of colored glass
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Idea An idea represents a thought or opinion, ranging from highly unformed to fully formed, that potentially shapes the design solution Ideas typically are the sole responsibility of the designer, though they may be inspired by many different sources Ideas change over time, and new ideas may or may not (partially) align with the current state of the design project
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Example ideas What if the luxury airplane had a shower on board?
Perhaps the library membership cards should have RFID tags, so a visitor can simply grab the books they want, walk by an automated scanner, and have their books be on loan I am thinking that the award should be a variant of last year’s award
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Design an instant message system
synthesize goals constraints assumptions decisions ideas analyze evaluate
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Design a word processor
synthesize goals constraints assumptions decisions ideas analyze evaluate
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Design the software to fly a drone
synthesize goals constraints assumptions decisions ideas analyze evaluate
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Design cycle at the micro level: design work
synthesize goals constraints assumptions decisions ideas analyze evaluate
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Design work Design work represents the individual or collaborative activity of engaging with a design project at a detailed level thinking articulating context analyzing alternative ideas identifying constraints making decisions setting goals …
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Opportunistic versus rationalistic design work
unexplored idea explored idea current decision
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Mixed opportunistic and rationalistic design work
unexplored idea explored idea current decision
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Backtracking unexplored idea previous decision explored idea
current decision
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Backtracking unexplored idea previous decision explored idea
current decision
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Simultaneous exploration
unexplored idea explored idea current decision
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Design an instant message system
synthesize goals constraints assumptions decisions ideas analyze evaluate
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Design a word processor
synthesize goals constraints assumptions decisions ideas analyze evaluate
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Design the software to fly a drone
synthesize goals constraints assumptions decisions ideas analyze evaluate
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Design cycle at the macro level: design process
synthesize goals constraints assumptions decisions ideas analyze evaluate
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Design process A design process represents a planned course of action as to how to tackle a design problem to arrive at a design solution where to focus effort what methods to use whom to involve A design process may be defined up-front in its entirety, or defined in increments as the design project unfolds
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Linear process what is it to accomplish? satisfactory experience
plan for realization change in the world what is it to accomplish? how does one interact with it? what is its conceptual core? what are its implementation details?
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Waterfall requirements phase design phase implementation phase
testing phase
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Waterfall as a design process
satisfactory experience plan for realization change in the world what is it to accomplish? how does one interact with it? what is its conceptual core? what are its implementation details?
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Agile Our highest priority is to satisfy the customer through early and continuous delivery of valuable software. Welcome changing requirements, even late in development. Agile processes harness change for the customer's competitive advantage. Deliver working software frequently, from a couple of weeks to a couple of months, with a preference to the shorter timescale. Business people and developers must work together daily throughout the project. Build projects around motivated individuals. Give them the environment and support they need, and trust them to get the job done. The most efficient and effective method of conveying information to and within a development team is face-to-face conversation. Working software is the primary measure of progress. Agile processes promote sustainable development. The sponsors, developers, and users should be able to maintain a constant pace indefinitely. Continuous attention to technical excellence and good design enhances agility. Simplicity—the art of maximizing the amount of work not done—is essential. The best architectures, requirements, and designs emerge from self-organizing teams. At regular intervals, the team reflects on how to become more effective, then tunes and adjusts its behavior accordingly.
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Agile as a design process
satisfactory experience plan for realization change in the world what is it to accomplish? how does one interact with it? what is its conceptual core? what are its implementation details?
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Other life cycle models
Extreme programming Rapid prototyping Spiral model Iterative development Rational unified process Synchronize-and-stabilize …
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Choosing a software life cycle
Choosing a software life cycle is choosing a design process One has to make sure the design process matches the nature of the design problem One has to make sure to remain flexible in adjusting the design process when the project so warrants
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Routine, adaptive, and original design projects
high original complexity adaptive routine low high low familiarity
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Design an instant message system
high original complexity adaptive routine low high low familiarity
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Design a word processor
high original complexity adaptive routine low high low familiarity
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Design the software to fly a drone
high original complexity adaptive routine low high low familiarity
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Realistic design process
satisfactory experience plan for realization change in the world what is it to accomplish? how does one interact with it? what is its conceptual core? what are its implementation details?
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Backtracking is inevitable here, too
satisfactory experience plan for realization change in the world what is it to accomplish? how does one interact with it? what is its conceptual core? what are its implementation details?
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Minimize backtracking
satisfactory experience plan for realization change in the world what is it to accomplish? how does one interact with it? what is its conceptual core? what are its implementation details? Strive to minimize backtracking more than absolutely necessary Strive to minimize backtracking later than absolutely necessary
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