	CS 580 Client-Server Programming Fall Semester, 2000 Introduction
	Lecture Notes Index © 2000, All Rights Reserved, SDSU & Roger Whitney San Diego State University -- This page last updated 26-Aug-00

Contents of Doc 1, Introduction

References

Code Complete by Steve McConnell


Doc 1, Introduction Slide # 2

Introduction to Course

Items To Cover

Prerequisites
Grades
Programs
Homework
Projects
Class notes, www
How lectures will work
Why this course
When will it be offered again?
Crashers
Machines, accounts, languages


Doc 1, Introduction Slide # 3

Computing "Paradigms"

Centralized Multi-user Architecture

Distributed Single-User Architecture

Client/Server Architecture

Centralized Multi-user Architecture

Large central computers serving many users


Doc 1, Introduction Slide # 4

Motivating Factors

Service large number of users (200 to 10,000+)
Centralized storage for large data bases
Minimize data on slow networks

Strengths

Very stable, very reliable, well supported
Cost-effective why to support thousands of users
Large pool of technical staff
Large number of business applications available

Weakness

Proprietary hardware and software
Very expensive
Requires large support staff
Costly to incrementally add more capacity

Mind Set

Hierarchical organization (Bureaucratic heaven)


Doc 1, Introduction Slide # 5

Distributed Single-User Architecture

Motivating Factors

Low cost fast local area networks
Provide small number of users with compute power
Failure of MIS departments to be responsive and cost-effective


Doc 1, Introduction Slide # 6

Strengths

Cheap hardware and software
Lots of third-party software
User is in complete control of environment
Low cost to add more users

Weakness

Sharing of resources across many users is difficult
Networks and OS do not provide good control or management over computer resources
Multivender environments can cause operation, support and reliability problems

Mind set

Individualism (Lone Ranger syndrome)


Doc 1, Introduction Slide # 7

Client/Server Architecture

Motivating Factors

Limitations of other modes of computing
Utilize easy to use micro computers as front end to mainframe computers


Doc 1, Introduction Slide # 8

Strengths


Cost-effective way to support thousands of users
Low cost to add more users
Cheap hardware and software
Provides control over access to data
User remains in control over local environment
Flexible access to information

Weaknesses

Reliability
Complexity
Lack of trained developers


Doc 1, Introduction Slide # 9

Introduction to Client-Server

What is Client-Server?

Client


Application that initiates peer-to-peer communication
Translate user requests into requests for data from server via protocol
GUI often used to interact with user

Server

Any program that waits for incoming communication requests from a client
Extracts requested information from data and return to client
Common Issues Authentication Authorization Data Security Privacy Protection Concurrency <HR>

Example: World Wide Web (WWW)

Data


Server normally provides data to clients
Often utilizes some data base
WWW data is HyperText Markup Language (html) files

<!DOCTYPE HTML SYSTEM "html.dtd">
<HTML>
<HEAD><TITLE>
Client Server Programming
</TITLE></HEAD>
<BODY>
<H2>Client Server Programming</H2>
<HR>
Doc 1, Introduction Slide # 10

Protocol

How the client and server interact
Glue that makes client-server work
Involves using low level network protocols and application specific protocols
Designing application specific protocols is very important
WWW uses the HyperText Transfer Protocol

Request = SimpleRequest | FullRequest

SimpleRequest = GET <uri> CrLf

FullRequest = Method URI ProtocolVersion CrLf
[*<HTRQ Header>]
[<CrLf> <data>]

<Method> = <InitialAlpha>

ProtocolVersion = HTTP/1.0

uri = <as defined in URL spec>

<HTRQ Header> = <Fieldname> : <Value> <CrLf>

<data> = MIME-conforming-message


Doc 1, Introduction Slide # 11

Protocol Choices

Text Based

Transmit ASCII or Unicode between machines HTTP is common transport layer XML becoming common SOAP new XML standard

Binary

Transmit objects between machines Faster development time RMI, Corba are examples


Doc 1, Introduction Slide # 12

What this Course is not
An advanced (or beginning) Networking course

How to use a client builder application/system

Powerbuilder

What this Course covers
Skills & knowledge required to build client-server applications


Doc 1, Introduction Slide # 13

What Client-Server Requires of a Programmer

Designing robust protocols

Network programming

Designing usable computer-human interfaces

Good documentation skills

Good debugging skills

Understand the information flow of the company/customer

Mastery of concurrency

Multi-platform development

Database programming

Security


Doc 1, Introduction Slide # 14

Programming Issues

Names

"Finding good names is the hardest part of OO Programming"

"Names should fully and accurately describe the entity the variable represents"

What role does the variable play in the program?

Data Structure	Role, function
InputRec	EmployeeData
BitFlag	PrinterReady

Some Examples of Names, Good and Bad

TrainVelocity	Velt, V, X, Train
CurrentDate	CD, Current, C, X, Date
LinesPerPage	LPP, Lines, L, X


Doc 1, Introduction Slide # 15

OOP Names - Common Problems

class Stack 
   {
   Vector theStack = new Vector();
   public void push( object x )
      {
      theStack.add( x );
      }
   // code deleted
   }
class DriverProgram 
   {
   public void static main( String[] args )
      {
      // blah blah blah
      Stack stack;
      aFooFunction( stack );
      // more blah
      }
   void aFooFunction( Stack aStack )
      {
      }
   }


Doc 1, Introduction Slide # 16

Comments

"Comments are easier to write poorly than well, and comments can be more damaging than helpful"
What does this do?

for i := 1 to Num do
 MeetsCriteria[ i ] := True;
for  i := 1 to Num / 2  do begin
 j := i + i;
 while ( j <= Num ) do begin
  MeetsCriteria[ j ] := False;
  j := j + i;
 end;
for i := 1 to Mun do
 if MeetsCriteria[ i ] then
  writeln( i, ' meets criteria ' );


Doc 1, Introduction Slide # 17

How many comments does this need?


for PrimeCandidate:= 1 to Num do
   IsPrime[ PrimeCandidate] := True;
for  Factor:= 1 to Num / 2  do begin
   FactorableNumber := Factor + Factor ;
   while ( FactorableNumber <= Num ) do begin
      IsPrime[ FactorableNumber ] := False;
      FactorableNumber := FactorableNumber + Factor ;
   end;
end;
for PrimeCandidate:= 1 to Num do
   if IsPrime[ PrimeCandidate] then
      writeln( PrimeCandidate, ' is Prime ' );

Good Programming Style is the Foundation of Well Commented Program


Doc 1, Introduction Slide # 18

Kinds of Comments

Repeat of the code

X := X + 1    /* add one to X
/* if allocation flag is zero */
if ( AllocFlag == 0 ) ...

Explanation of code

Used to explain complicated or tricky code

*p++->*c = a
/* first we need to increase p by one, then ..


Make code simpler before commenting

(*(p++))->*c = a
ObjectPointerPointer++;
ObjectPointer = *ObjectPointerPointer;
ObjectPointer ->*DataMemberPointer = a;


Doc 1, Introduction Slide # 19

Marker in the code

/*  **** Need to add error checking here  **** */

Summary of the code

Distills a few lines of code into one or two sentences

Description of the code's intent

Explains the purpose of a section of code

{ get current employee information }   intent
{ update EmpRec structure }     what


Doc 1, Introduction Slide # 20

Commenting Efficiently

Use styles that are easy to maintain

/***********************************
 * module: Print                   *
 *                                 *
 * author: Roger Whitney           *
 * date:   Sept. 10, 1995          *
 *                                 *
 * blah blah blah                  *
 *                                 *
 ***********************************/
/***********************************
  module: Print          
                         
  author: Roger Whitney  
  date:   Sept. 10, 1995 
                         
  blah blah blah         
                         
 ***********************************/

Comment as you go along


Doc 1, Introduction Slide # 21

Commenting Techniques

Commenting Individual Lines

Avoid self-indulgent comments

MOV AX,  723h        ;    R. I. P. L. V. B.

Endline comments have problems

MemToInit := MemoryAvailable(); { get memory available }

Not much room for comment
Must work to format the comment

Use endline comments on

Data declarations
Maintenance notes
Mark ends of blocks


Doc 1, Introduction Slide # 22

Commenting Paragraphs of Code

Write comments at the level of the code's intent

Comment the why rather than the how

Make every comment count

Document surprises

Avoid abbreviations

How verses Why
How

/* if allocation flag is zero */
if ( AllocFlag == 0 ) ...

Why

/* if allocating a new member */
if ( AllocFlag == 0 ) ...

Even Better

/* if allocating a new member */
if ( AllocFlag == NEW_MEMBER ) ...


Doc 1, Introduction Slide # 23

Summary comment on How

{ check each character in "InputStr" until a 
  dollar sign is found or all characters have 
  been checked }
Done   := false;
MaxPos := Length( InputStr );
i      := 1;
while ( (not Done) and (i <= MaxLen) ) begin
   if ( InputStr[ i ] = '$' ) then
      Done := True
   else
      i := i + 1
end;

Summary comment on Intent

{ find the command-word terminator }
Done   := false;
MaxPos := Length( InputStr );
i      := 1;
while ( (not Done) and (i <= MaxPos ) ) begin
   if ( InputStr[ i ] = '$' ) then
      Done := True
   else
      i := i + 1
end;


Doc 1, Introduction Slide # 24

Summary comment on Intent with Better Style

{ find the command-word terminator }
FoundTheEnd      := false;
MaxCommandLength := Length( InputStr );
Index            := 1;
while ((not FoundTheEnd) and 
       (Index <= MaxCommandLength)) begin
   if ( InputStr[ Index ] = '$' ) then
      FoundTheEnd := True;
   else
      Index := Index + 1;
end;


Doc 1, Introduction Slide # 25

Commenting Data Declarations

Comment the units of numeric data

Comment the range of allowable numeric values

Comment coded meanings

var
   CursorX:      1..MaxCols;   { horizontal screen position of cursor }
   CursorY:      1..MaxRows;   { vertical position of cursor on screen }
   AntennaLength:   Real;   { length of antenna in meters: >= 2 }
   SignalStrength:   Integer;   { strength of signal in kilowatts: >= 1 }
   CharCode:      0..255;   { ASCII character code }
   CharAttib:      Integer;   { 0=Plain; 1=Italic; 2=Bold  }
   CharSize:         4..127;   { size of character in points }
Comment limitations on input data
Document flags to the bit level


Doc 1, Introduction Slide # 26

Commenting Routines

Avoid Kitchen-Sink Routine Prologs

Keep comments close to the code they describe

Describe each routine in one or two sentences at the top of the routine

Document input and output variables where they are declared

Differentiate between input and output data

Document interface assumptions

Keep track of the routine's change history

Comment on the routine's limitation

Document the routine's global effects

Document the source of algorithms that are used

procedure InsertionSort 
   {
   Var   Data:      SortArray;    { sort array elements }
      FirstElement:   Integer        {index of first element to sort}
      LastElement:   Integer        {index of last element to sort}
   }


Doc 1, Introduction Slide # 27

Object-Oriented Programming

Conceptual Level DefinitionAbstraction
“Extracting the essential details about an item or group of items, while ignoring the unessential details.”
Edward Berard

“The process of identifying common patterns that have systematic variations; an abstraction represents the common pattern and provides a means for specifying which variation to use.”
Richard Gabriel

Example

Pattern:    Priority queue
Essential Details:   length 
   items in queue 
   operations to add/remove/find item
Variation:   link list vs. array implementation
   stack, queue


Doc 1, Introduction Slide # 28

Object-Oriented Programming Conceptual Level DefinitionEncapsulation

Enclosing all parts of an abstraction within a container

Example


Doc 1, Introduction Slide # 29

Object-Oriented Programming Conceptual Level DefinitionInformation Hiding

Hiding parts of the abstraction

Example


Doc 1, Introduction Slide # 30

Object-Oriented Programming Conceptual Level DefinitionHierarchy
Abstractions arranged in order of rank or level

Class Hierarchy


Doc 1, Introduction Slide # 31

Object-Oriented Programming Conceptual Level DefinitionHierarchy

Object Hierarchy

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