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.

Discussion There will be discussion this Friday Please join your designated discussion Note new classroom: SE2 1304

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

Today Defining design Feasibility and desirability Four types of design Design cycle

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

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.

Design designer plan maker change in the world other stakeholders audience experiences

Design a luxury airplane designer plan maker change in the world other stakeholders audience experiences

Design a library designer plan maker change in the world other stakeholders audience experiences

Design an award designer plan maker change in the world other stakeholders audience experiences

Design fields Architecture design Graphic design Fashion design Game design Chip design Car design Urban design Product design Interior design …

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 …

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

Design designer plan maker change in the world other stakeholders audience experiences

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]

Feasibility and desirability designer plan maker change in the world other stakeholders audience experiences

Feasibility and desirability designer plan maker change in the world other stakeholders audience experiences desirability

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?

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?

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

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

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

Design problem and solution design solution

Design project design problem design solution design project

Design cycle synthesize analyze evaluate

Design cycle goals constraints assumptions decisions ideas synthesize analyze evaluate

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

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

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

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

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

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

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

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

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

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

Design an instant message system synthesize goals constraints assumptions decisions ideas analyze evaluate

Design a word processor synthesize goals constraints assumptions decisions ideas analyze evaluate

Design the software to fly a drone synthesize goals constraints assumptions decisions ideas analyze evaluate

Design cycle at the micro level: design work synthesize goals constraints assumptions decisions ideas analyze evaluate

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 …

Opportunistic versus rationalistic design work unexplored idea explored idea current decision

Mixed opportunistic and rationalistic design work unexplored idea explored idea current decision

Backtracking unexplored idea previous decision explored idea current decision

Backtracking unexplored idea previous decision explored idea current decision

Simultaneous exploration unexplored idea explored idea current decision

Design an instant message system synthesize goals constraints assumptions decisions ideas analyze evaluate

Design a word processor synthesize goals constraints assumptions decisions ideas analyze evaluate

Design the software to fly a drone synthesize goals constraints assumptions decisions ideas analyze evaluate

Design cycle at the macro level: design process synthesize goals constraints assumptions decisions ideas analyze evaluate

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

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?

Waterfall requirements phase design phase implementation phase testing phase

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?

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.

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?

Other life cycle models Extreme programming Rapid prototyping Spiral model Iterative development Rational unified process Synchronize-and-stabilize …

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

Routine, adaptive, and original design projects high original complexity adaptive routine low high low familiarity

Design an instant message system high original complexity adaptive routine low high low familiarity

Design a word processor high original complexity adaptive routine low high low familiarity

Design the software to fly a drone high original complexity adaptive routine low high low familiarity

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?

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?

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