Design Practices

Design

• Practices

• Principles

• Patterns

What are the characteristics of good design?

What are good solutions to common design problems?

How do we go about design and what do we produce?

cs121 design

• Game

• User interface

• Software

• Test plan

• ++

This is well underway.

But what is design?

design: the verb

“Design is the planning that lays the basis for the making.”

-wikipedia

design: the noun

“Blueprint, something intended as a guide for making something else.”

- google define:design

“Plans are worthless. Planning is priceless.”

-eisenhower

design: the noun

“Features of shape, configuration, pattern, or ornamentation that can be judged by the eye in finished products. “

-NASA

design a la cs121

• noun: a model that captures the essential properties of a thing

• verb: the practice of “creating” a design to solve some problem

verbs: Model ≠ Design

Requirements models Documentation

project start project end

Design models

what should it do how will it do it how is it does it

Design is a creative, problem-solving process!Design models are predictive.

design

create the piece to create the picture

how do we go about design?

• model

• review (critique)

• repeat

until everyone is happy “enough”

Waterfall Model

Requirements

Design

Implementation

Test

with feedback

Iterative Development

In each iteration:• Identify the objectives of the iteration• Design a solution to achieve the objectives• Implement the solution• Test the implementation

we talked about this last time

Agile requirementsAt the start of each iteration: • Incorporate new goals (often produced by last iteration)• Remove goals no longer needed• Reprioritize• Clarify requirements for goals at top of stack• Plan iteration

highest priority goal

lowest priority goal

Iterative Development

In each iteration:• Identify the objectives of the iteration• Design a solution to achieve the objectives

• Model solution• Review• Repeat until good enough

• Implement the solution• Test the implementation

agile design

design for now design for later

agile design

design skeleton add meat

early iterations later iterations

…

don’t expect to get everything right the first time!

CS121 project landmarks

alpha beta v1

stable architecture,stable GUI

game for user testing release to customer

Design

• Practices

• Principles

• Patterns

What are the characteristics of good design?

What are good solutions to common design problems?

How do we go about design and what do we produce?

Forms of models

• Text (hyperlinked)

• Diagrams, charts, graphs

• Prototypes

• Mathematical models

Agile models

• Know your purpose

• Choose the simplest form that works

• Know when to throw it away

Forms of models

• Text (hyperlinked)

• Diagrams, charts, graphs

• Prototypes

• Mathematical models

GDD

Forms of models

• Text (hyperlinked)

• Diagrams, charts, graphs

• Prototypes

• Mathematical models

Unified Modeling Language

The UML is a standard language for visualizing, specifying, constructing, and documenting the artifacts of a software system.

Domain model

CourseCourse Offering

Instructor

StudentTextbookTime Slot

Room

Meeting

Class List

Author

Department College

Major

Building

Semester

uses

written by

“Domain” model

PlayerPacman

Screen grid

moves

Grid Cell

positioned on

has aType

Level

has a

lives score

Design model

• Major classes

• Responsibility of each class

• Interactions of classes

Design model (work in progress)

PlayerSpriteLivesScoreCurrent cellMove()

Sprite

LevelCells

GameLevel

Cell

Blank cell Ghost cell Dot cell

Domain Design

CRC cards: design method for OO– Class– Responsibilities– Collaboration

“Act out use cases”

CRC Cards Technique(Responsibility-Driven Design)

• Informal, non-detailed

• Used for group brain-storming

• End result is a first cut at design model

• Not intended to provide a complete design

The Basic Idea

• Develop set of index cards. • Each card represents one design class.• A card contains:

– The name of the class.

– The responsibilities of the class.

– Collaborations: other classes with which this class interacts and its responsibilities in the interaction

Format of CRC cards

Responsibilities

___________

___________

____________

Class Namesuper class

sub-classes

Collaborations

____________

____________

____________

Limiting the size of a card is an attempt at preventingthe class from becoming too complex.

Pac Man move use case

Move:1. Player moves Pac Man left, right, up, down2. Pac Man moves to new space 2a Attempted move prohibited by wall, no movement3. New space is blank3a. New space has dot but not last dot, 50 points awarded3b. New space has last dot, 50 points awarded, new level

starts3c. New space has ghost, life decreases by 1, if last life

game ends

“Domain” model

PlayerPacman

Screen grid

moves

Grid Cell

positioned on

has aType

Level

has a

lives score

Domain classes

• Player• Pacman• Score• Lives• Level• Screen grid• Grid Cell• Cell type

Player CRC card

PlayerClass

Player CRC card

Player super class:

sub-classes:

Super- and Sub-classesif any

Player CRC card

Move

Remember score

Remember number of lives

Player

Responsibilities

Player CRC card

Move

Remember score

Remember number of lives

Player

Collaborationscollaborate with ?

“Domain” model

PlayerPacman

Screen grid

moves

Grid Cell

positioned on

has aType

Level

has a

lives score

Responsibilities

• Player• Pacman• Score• Lives• Level• Screen grid• Grid Cell• Cell type

remember current cell, draw self

Responsibilities

• Player• Pacman• Score• Lives• Level• Screen grid• Grid Cell• Cell type

maybe these should be “attributes” of the player class rather than proper classes

Attribute vs. Collaboration

• An object of a class typically has one or more attributes.

• Attributes have values that specify or describe the object.

• A value might or might not deserve the distinction of being an object itself.

• A would-be attribute that is object-valued is actually a collaboration.

Design model: how does move work?

PlayerSpriteLivesScoreCurrent cellMove()

Sprite

LevelCells

GameLevel

Cellposition

Blank cell Ghost cell Dot cell

Design model: how does move work?

PlayerSpriteLivesScorePositionMove()

Sprite

LevelCells

GameLevel

Cellposition

Blank cell Ghost cell Dot cell

Design model: how does move work?

PlayerSpriteLivesScoreMove()

Sprite

LevelCellsCurrent cell

GameLevel

Cellposition

Blank cell Ghost cell Dot cell

How to decide

• Design principles

• Design patterns

Design class models

attributes

responsibilities

Student

ID

registers

name

Class models

Our models evolve ...

data

methods

Student

int ID

void registers()

name

Class models: aggregation/composition

Student

int IDcourse courseList

void registers()

Course

course ID

“has a”

1,…

Class model: Inheritance

Student

int ID

void registers()

Part Time Student

int ID

void registers()

Full Time Student

int ID

void registers()

Use case realization: Sequence diagram

Student Registrar Course list

register( int classID) course.stillOpen(classID)

true…

Design classes Software classes

implement

UML documents

UML

• Capture important classes, responsibilities, collaborations

• Often omit unnecessary detail:– e.g. helper classes like lists

Classification of UML• User model view

– use case diagrams

• Structural model view– class diagrams

– object diagrams

• Behavioral model view– sequence diagrams

– collaboration diagrams

– state machine diagrams

– activity diagrams

• Implementation model view– component diagrams

• Environment model view– deployment diagrams

Forms of models

• Text (hyperlinked)

• Diagrams, charts, graphs

• Prototypes

• Software (e.g. proofs of concepts)

• Mathematical models

good form for “testing” design

Prototypes

• Communicate

“These are the basics of the game…”

Prototypes

• Communicate

• Resolve technical risks

“We know how to detect collisions.”

Prototypes

• Communicate

• Resolve technical risks

• Evaluate/test

“This is how the screens will look. What do you think?”

Prototypes

• Communicate

• Resolve technical risks

• Evaluate/test

• Iterative design/development strategy

Prototype 1Prototype 0Prototype n

= v.1…

Agile modeling principles

• Know your purpose

• Choose the simplest form that works

• Know when to throw it away

These apply to prototypes

Prototyping principles

• Know your purpose

Make concrete your vision for the customerIs our core gameplay fun? Is pygame collision detection fast enough?

Prototyping principles

• Know your purpose and expected outcomes

Make concrete your vision for the customer. Verbal feedback.

Is our core gameplay fun? User questionnaire.

Is pygame collision detection fast enough? Calculate FPS vs. # sprites (50x50) in full screen mode.

Prototyping principles

• Know your purpose and expected outcomes

• Choose the simplest form that works

Prototyping principles

• Know your purpose and expected outcomes

• Choose the simplest form that works

UI mockupsstoryboards

Prototyping principles

• Ask a question

• Devise a test protocol or metric

• Choose the simplest form that works

software executables(try prototyping tools like Gamemaker and pygame)

Prototyping principles

• Ask a question

• Devise a test protocol or metric

• Choose the simplest form that works

• Know when to throw it away

Prototyping principles

• Ask a question

• Devise a test protocol or metric

• Choose the simplest form that works

• Know when to throw it away or refactor

change the internal structure without affecting the external behavior

Mathematical Models

• Algebraic models: i.e. FPS(# sprites)• Combinatoric models: i.e. #winning strategies• Probabilistic models:

i.e. Prob(A wins | weapons of A and B)• Simulation

how do we go about design?

• model

• review (critique)

• repeat

Next time: Formal design reviews

Next time

• Design reviews

• Intro to Design principles