CS 596: Intro Lecture

CS 596 Client-Server Programming
Intro Lecture

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San Diego State University -- This page last updated January 29, 1996

Contents of Intro Lecture

Introduction to Course

Items To Cover

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

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

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>

Protocol

How do the client and server interact

This is the glue that make 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

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

How to use a client builder application/system

Powerbuilder

What this Course covers
The skills and knowledge required to build client-server applications

The Client-Server University (CSU) is building a Virtual Campus (VC) where students and instructors interact via the Internet.

CSU needs some help in implementing programs to facilitate activities that currently occur in person.

Posting Grades During the Semester Faculty currently post grades on their office doors during the semester to let students know how they are doing.

Submitting Final Grades to Registrar Faculty currently bring signed formalized documents to the registrar with final grades.

Office Hours Students currently come to faculty offices.

Student Board Game Club Students currently go to the student union to play chess, checkers and go

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

Nintendo

*

X := X + 1 /* add one to X

Comments

"Comments are easier to write poorly than well, and comments can be more damaging than helpful"

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;

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

Programming
Progamming is a process that produces products

Products

source code
documentation
design
tools

Programming is a skill like writing or playing musical instrument

How does one develop a skill?

What is our metric to measure how well we program?

Criteria for Evaluating for Modularity

Decomposability

Decompose problem into smaller subproblems that can be solved separately

Example: Top-Down Design

Counter-example: Initialization Module

Criteria for Evaluating for Modularity Composability

Freely combine modules to produce new systems

Examples: Math libraries
Unix command & pipes

Criteria for Evaluating for Modularity Understandability

Individual modules understandable by human reader

Counter-example: Sequential Dependencies

Criteria for Evaluating for Modularity Continuity

Small change in specification results in:

Changes in only a few modules

Does not affect the architecture

Example: Symbolic Constants

const MaxSize = 100

Criteria for Evaluating for Modularity Protection

Effects of an abnormal run-time condition is confined to a few modules

Example: Validating input at source

Computing "Paradigms"

Centralized Multi-user Architecture

Distributed Single-User Architecture

Client/Server Architecture

Centralized Multi-user Architecture

Large central computers serving many users

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)

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

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)

Client/Server Architecture

Motivating Factors

Limitations of other modes of computing

"Cool" applications like WWW

Utilize easy to use micro computers as front end to mainframe computers

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 Maturity

Lack of trained developers

Politics
A threat to the bureaucrats and the lone rangers

CS 596 Client-Server Programming Intro Lecture

Contents of Intro Lecture

CS 596 Client-Server Programming
Intro Lecture