Software Design i206 Fall 2010 John Chuang Some slides adapted from Glenn Brookshear, Brian Hayes, Marti Hearst, or James Landay.

Software Design

i206 Fall 2010

John Chuang

Some slides adapted from Glenn Brookshear, Brian Hayes, Marti Hearst, or James Landay

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SoftwareDesign

Bits & BytesBinary Numbers

Number Systems

Gates

Boolean Logic

Circuits

CPU Machine Instructions

Assembly Instructions

Program Algorithms

Application

Memory

Data compression

Compiler/Interpreter

OperatingSystem

Data Structures

Analysis

I/O

Memory hierarchy

Design

Methodologies/Tools

Process

Truth tableVenn DiagramDeMorgan’s Law

Numbers, text,audio, video, image, …

Decimal, Hexadecimal, Binary

AND, OR, NOT, XOR, NAND, NOR,etc.

Register, CacheMain Memory,Secondary Storage

Context switchProcess vs. ThreadLocks and deadlocks

Op-code, operandsInstruction set arch

Lossless v. lossyInfo entropy & Huffman code Adders, decoders,

Memory latches, ALUs, etc.

DataRepresentation

Data

Data storage

Principles

ALUs, Registers,Program Counter, Instruction Register

Network

Distributed Systems Security

Cryptography

Standards & Protocols

Inter-processCommunication

Searching, sorting,Encryption, etc.

Stacks, queues,maps, trees, graphs, …

Big-O

UML, CRC

TCP/IP, RSA, …

ConfidentialityIntegrityAuthentication…

C/S, P2PCaching

sockets

Formal models

Finite automataregex

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Outline (Next 5 Weeks)

Algorithm and Program Programming Languages and Paradigms Object-Oriented Design Analysis of Algorithms Data Structures Regular Expressions

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Algorithm and Program

An algorithm is an ordered set of unambiguous, executable steps that defines a terminating process.- named after 9th century Persian mathematician Abu Ja'far Mohammed ibn Musa al-Khowarizmi

A computer program is a representation of an algorithm which prescribes the actions that are to be carried out by a computer. - A computer program consists of a set of instructions that the computer understands.

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Algorithms: Levels of Abstraction

Problem: motivation for algorithm

Algorithm: procedure to solve the problem- Often one of many possibilities

Representation: description of algorithm sufficient to communicate it to the desired audience- Always one of many possibilities

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Folding a Bird from a Square Piece of Paper

Source: Brookshear

Origami Primitives

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Sequential Search Algorithm in Pseudocode

Source: Brookshear

Pseudocode primitives in bold

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Algorithm and Program

An algorithm is an ordered set of unambiguous, executable steps that defines a terminating process.

A computer program is a representation of an algorithm which prescribes the actions that are to be carried out by a computer. - A computer program consists of a set of instructions that the computer understands.

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Programming Languages

Machine language (1st generation) Assembly language (2nd generation)

- Simply a set of abbreviations for the machine code instructions- An assembler is used to translate the program into machine instructions

High-level language- A compiler or an interpreter is used to translate the program into

machine instructions

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http://xkcd.com/303/

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Programming Paradigms

Imperative programming- describes computation in terms of statements that change a program state

- Consistent with the sequential execution of instructions in hardware

- E.g., procedural programming, object-oriented programming

Declarative programming- Describe desired results, without explicit description of steps

- E.g., regular expressions, functional programming, logical programming

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Imperative Programming

Procedural programming- Specifies a sequence of algorithmic steps- Use of procedures (aka routines, subroutines, functions, or methods) to improve modularity, reuse

Object-oriented programming- Specifies a collection of objects, each with its own data and methods, and the collaborations between the objects

- OOP promotes modularity and reuse via abstraction, encapsulation, inheritance

- Helps keep large software projects, and projects with changing requirements, manageable

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OOP Example

Source: http://www.stanford.edu/~gpathy/umlshort/

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Object-Oriented Design

Object-oriented design based upon principles of abstraction, encapsulation, and modularity

Object-oriented design through the clarification of object roles, responsibilities, and collaborations

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Role and Responsibility

Application: a set of interacting objects Object: an implementation of one or more roles Role: a set of related responsibilities Responsibility: an obligation to perform a task (action) or to know information (data)

Source: Wirfs-Brock and McKean, Object Design: Roles, Responsibilities, and Collaborations.

an object

knows information performs services

maintains connections(to other objects)

makes decisions(to do the right things)

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Collaboration

Collaboration: an interaction of objects or roles (or both)

Contract: an agreement outlining the terms of a collaboration

Source: Wirfs-Brock and McKean, Object Design: Roles, Responsibilities, and Collaborations.

a collaborator

knows information performs services

maintains connections(to other objects)

makes decisions(to do the right things)

an object

needs help

message asking for help

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Cohesion and Coupling Q: how to come up with the right set of objects for a system?- Maximize cohesion (relationship within object)- Minimize coupling (relationship between objects)

ALU

SHIFTER

RegistersALU

Shifter

Chip 1 Chip 2

Chip 3

1. Design using 3 chips (classes)Chip 1 Chip 2

Chip 3

AND gates OR gates

NOT gates

2. Design using 3 chips (classes)

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Cohesion and Coupling

Design 2 has too much coupling and not enough cohesion. As a result, it is:- difficult to understand- difficult to locate faults- difficult to reuse, extend, or enhance

Design 1 has better abstraction, encapsulation, and modularity

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OO Analysis & Design Process

Gather requirements Develop use cases

- Each use case describes what the system does to accomplish a particular customer goal

Analysis and Design- Iterative process of identifying roles, responsibilities, and collaborations

- Textual analysis- Noun analysis to identify candidate classes- Verb analysis to identify candidate methods

- Identification and use of design patterns- Design pattern: a general reusable solution to a commonly occurring problem

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Unified Modeling Language (UML) UML is a language for specifying, visualizing, constructing, and documenting a software system

Several types of diagrams, including:- Use Case diagrams- Class diagrams- Sequence diagrams- …

http://www.smartdraw.com/resources/centers/uml/uml.htm

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Use Case Diagram A use case is a sequence of

actions a system performs that yields an observable result to an external actor- A use case describes

functionality of the system from the user's point of view

- A good use case has: a single goal, an external initiator, a start condition, and an end condition

- A use case is represented by an oval in UML

An actor is someone or something outside the system that interacts with the system- An actor can be a human being

or another system or a device- An actor is represented by a

stick figure in UML.

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Class Diagram

Captures the logical structure of the system, including objects and their relationships with one another

Source: Brookshear, Figure 7.4

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Class Diagram Example

Source: http://www.stanford.edu/~gpathy/umlshort/

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+: public - : private

Representing Classes

Source: Learning UML 2.0

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Representing Classes

Source: Learning UML 2.0

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Relationships between Classes

Source: Learning UML 2.0

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Relationships between Classes

Source: Learning UML 2.0

“HAS-A”

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Relationships between Classes

Source: Learning UML 2.0

Note: Inheritance is also known as generalization

“IS-A”

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Class Diagram Example

Source: http://www.stanford.edu/~gpathy/umlshort/

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Collaboration Diagram

Shows interactions between classes for one or more use cases

Source: Brookshear, Figure 7.6

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Sequence Diagram

Shows interactions between classes over time for a particular use case

Place classes at the top of diagram

Draw vertical lines down from each class

Draw horizontal lines to the vertical lines to show interactions (method calls); label lines with the name of the message or method- Time goes from diagram’s top to bottom

Source: Wikipedia

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Software Design Process Software design is a creative problem solving process

- Understand the problem (create use scenarios)- Find algorithmic procedure that might solve the problem

(consider different solution options)- Formulate the algorithm and represent it as a program- Evaluate the program for accuracy and its potential as a

tool for solving other problems- Iterate!

Source: Brookshear, Figure 7.2 http://www.math.bas.bg/~nkirov/2004/Horstman/ch13/images/spiral.png

Traditional Software Life Cycle