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

John Chuang2 Software Design Bits & Bytes Binary Numbers Number Systems Gates Boolean Logic Circuits CPU Machine Instructions Assembly Instructions Program Algorithms Application Memory Data compression Compiler/ Interpreter Operating System Data Structures Analysis I/O Memory hierarchy Design Methodologies/ Tools Process Truth table Venn Diagram DeMorgan’s Law Numbers, text, audio, video, image, … Decimal, Hexadecimal, Binary AND, OR, NOT, XOR, NAND, NOR, etc. Register, Cache Main Memory, Secondary Storage Context switch Process vs. Thread Locks and deadlocks Op-code, operands Instruction set arch Lossless v. lossy Info entropy & Huffman code Adders, decoders, Memory latches, ALUs, etc. Data Representation Data storage Principles ALUs, Registers, Program Counter, Instruction Register Network Distributed Systems Security Cryptography Standards & Protocols Inter-process Communication Searching, sorting, Encryption, etc. Stacks, queues, maps, trees, graphs, … Big-O UML, CRC TCP/IP, RSA, … Confidentiality Integrity Authentication … C/S, P2P Caching sockets Formal models Finite automata regex

John Chuang3 Outline (Next 5 Weeks)  Algorithm and Program  Programming Languages and Paradigms  Object-Oriented Design  Analysis of Algorithms  Data Structures  Regular Expressions

John Chuang4 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.

John Chuang5 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

John Chuang6 Folding a Bird from a Square Piece of Paper Source: Brookshear Origami Primitives

John Chuang7 Sequential Search Algorithm in Pseudocode Source: Brookshear  Pseudocode primitives in bold

John Chuang8 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.

John Chuang9 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 Source: Brookshear, Figure 6.2

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John Chuang11 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

John Chuang12 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

John Chuang13 OOP Example Source:

John Chuang14 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

John Chuang15 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)

John Chuang16 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

John Chuang17 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) 1. Design using 3 chips (classes) 2. Design using 3 chips (classes)

John Chuang18 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

John Chuang19 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

John Chuang20 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 -…

John Chuang21 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.

John Chuang22 Class Diagram  Captures the logical structure of the system, including objects and their relationships with one another Source: Brookshear, Figure 7.4

John Chuang23 Class Diagram Example Source:

John Chuang24 +: public - : private Representing Classes Source: Learning UML 2.0

John Chuang25 Representing Classes Source: Learning UML 2.0

John Chuang26 Relationships between Classes Source: Learning UML 2.0

John Chuang27 Relationships between Classes Source: Learning UML 2.0 “HAS-A”

John Chuang28 Relationships between Classes Source: Learning UML 2.0 Note: Inheritance is also known as generalization “IS-A”

John Chuang29 Class Diagram Example Source:

John Chuang30 Collaboration Diagram  Shows interactions between classes for one or more use cases Source: Brookshear, Figure 7.6

John Chuang31 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

John Chuang32 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 Traditional Software Life Cycle