2440: 141 Web Site Administration Web Application Resources Instructor: Enoch E. Damson.

The University of AkronSummit College

Business Technology Dept.2440: 141

Web Site Administration

Web Application ResourcesInstructor: Enoch E. Damson

Client/Server BasicsThe client/server model generally has clients and servers, and

business/application logic (rules)Client – hardware or software used to communicate with a data

provider (server) Normally, one user uses a specific client at a time

Server – a computer capable of providing data to many clients at the same time The term server can mean:

the physical computer or piece of hardware the actual server software or daemon running on that machine

Daemon – a program that offers a service to other programs, usually over a network

Application/business logic – rules written in a programming language to help the communication between clients and the server

Web Application Resources 2

Network Connections and PortsComputers connected to the Internet typically

communicate using TCP/IP (Transmission Control Protocol and the Internet Protocol)TCP/IP – allows computers to communicate at a network-

level using IP (Internet Protocol) addresses TCP (Transmission Control Protocol) – invented by Robert Kahn IP (Internet Protocol) – created by Dr. Vinton Cert together with

Robert Kahn


Network Connections and Ports…IP Address – a unique identifier assigned to each

computer on the InternetPort number – a unique identifier that indicates each

service running on a computerMost services have standard port numbersSome standard ports numbers are:

ftp (20,21), telnet (23), smtp (25), http (80)


Web ServersService client requests for documentsThe European Lab for Particle Physics (CERN) produced one of

the first Web serversThe World Wide Web Consortium (W3C) took over the

development of the CERN HTTPD (W3C HTTPD)The National Center for Supercomputing Applications (NCSA)

also created an HTTP server which quickly became popular between 1993 and 1995

The Apache server (based on the NCSA implementation) has become very popular


Web BrowsersUsed as a client to retrieve and display information

from Web serversEarlier Web browsers were text-based

E.g. gopher, WAIS, telnet, FTPNCSA Mosaic was the first real HTML browser that

was developed in 1993There are several browsers on the market now


Electronic PublishingThe two main types of files in Web publishing are:

ASCII Text Files – uses numeric values (0 – 127) to represent letters, numbers, and other characters Each byte of the file represents a specific character

Binary Files – contain images, sounds, compressed ASCII text, etc


ImagesThere are several file formats available for storing graphics and

imagesWeb browsers support just a few image formatThe most common type of formats are:

GIF (Graphic Interchange Format) – mostly used for graphics (like clip arts logos, icons, etc) requiring fewer colors because it displays only 256 colors

JPEG/JPG (Joint Photographic Expert Group) – mostly used for photographs and images covering a wide spectrum of color because it uses the full 16.7 million colors

PNG (Portable Network Graphic) – offer millions of colors, lossless compression, and other features that make them a good alternative to GIF images in most cases


AudioEmbedded in Web applications to play automatically,

or used as links to be played when a user clicks on a link to the sound file

Some of the common sound files include:WAV – originated on Windows-based machinesAIFF – originated on MacintoshAU – originated on Sun Microsystems workstations (UNIX)


Multipurpose Internet Mail Extensions (MIME) TypesSet of rules that allow multimedia documents to be

exchanged among many different computer systemsOriginally designed for sending email attachments

and incorporated into httpBoth the Web server and the Web browser must

have a MIME types database Mime type database – used to identify the file extension

and determine how the file must be sent


The Hypertext Transfer Protocol (HTTP)Provides a standard way of communication and information

exchange between the Web browsers and Web servers Expects the client to initiate a request and the server to

respondEach request and response has three parts:

Request/Response line – contains a request method, the document location, and the protocol version

Header section – series of lines with http headers that are used to pass other information about the request and the client to the server

Entity body – contains other data to be passed to the server


HTTP Request/Response ExampleClient Request

GET /hello.html HTTP/1.1Host: test.comUser-Agent: Morzilla/4.5

Server ResponseHTTP/1.1 200 OK

Date: Wed, 06 Sept 2006 13:56:05 GMTLast-Modified: Wed, 06 Sept 2006 13:50:23 GMTServer: Apache/2.0.52Connection: closeContent-Length: 25Content-Type: text/html

<html>Hello world!</html>


HTTP Request/Response Example…Client Request

The hello.html file was requested from the server test.com using HTTP version 1.1

the Web browser used was Mozilla version 4.5

Server ResponseThe request was successful

(status code 200) and returned 25 bytes of text

The server indicates the date and time it thinks the resource was requested and last modified and the software it is running (Apache version 2.0.52)


HTTP Request MethodsThe HTTP command of the Web browser’s request

lineThe Web server uses the request method to

determine what to do with the browser’s requestThere are several methods defined by the HTTP 1.1

standard but only a few are widely supported by the HTTP serversThe most widely used methods are:

GET – for retrieving information from a Web server Can also be used to pass information to the Web server as part of a URL

HEAD – for verifying the existence of information on a Web server POST – for sending (updating) information to a Web server


HTTP Request Methods…Other http methods include:

PUTDELETETRACETRACKOPTIONS CONNECT


HTTP Server ResponsesProcess client requestsThe server generates an error if the resource requested

cannot be locatedThe response line of the server response has 3 parts:

Protocol version – should always be HTTP withStatus code – a three-digit indicator result code defined by the HTTP

specification The first digit represents the category of the response There are currently five categories:

Informational – the request was received and is being processed Success – the client request was successful Client error – the client’s request was incomplete or incorrect Server error – the request was not fulfilled due to a server problem

Description phrase


Common Response CodesInformational 1xx

100 Continue – the initial part of the request has been received and the client should continue

200 OK – the client’s request was successful and the server’s response contains the resource requested

204 No Content – The request was successful but the response is empty

Redirection 3xx301 Moved Permanently – the URL requested is no longer valid302 Found (Moved Temporarily) – the URL requested currently resides

in a different location304 Not Modified – the client performed a conditional GET and the

document has not been modified


Common Response Codes…Client Error 4xx

400 Bad Request – the server could not understand the request

403 Forbidden – the client requested data that it did not have permission to access

404 Not Found – the resource requested was not found on the server

Server Error 5xx500 Internal Server Error – something unexpected

happened on the server side


HTTP HeadersUsed to transfer Information between the client and

serverHas a name and value associated with itThere is one header per line


Common Request HeadersAccept – specifies the client’s preferred media typeCookie – contains cookie information (name/value

pair) for the requested URLIf-Modified-Since – used for a conditional GET

request (when a document has been modified)Referrer – allows the client to specify the URL of the

page from which the currently requested URL was obtained

User-Agent – identifies the Web browser software


Common Response HeadersServer – identifies the server softwareSet-Cookie – Allows the server to set a cookie on the

client browser (when permitted) for the given URL or domain


Common Entity HeadersContent-Length – specifies the size (in bytes) of the data

transferred in the entity bodyContent Type – specifies the MIME Type of the data

returned in the entity bodyExpires – specifies the date/time after which the

response is considered outdatedLast-Modified – specifies the date/time the document

was last modified


Other Web-Related ServersSome of the most common servers that run along HTTP

servers are:Proxy serversStreaming Audio/VideoFile Transfer Protocol (FTP)DatabasesSecure Socket Layer (SSL)


Proxy ServersAn intermediary server between a client and destination

serverAllows extra processing of returned dataHave three main uses:

Security – act as a firewall by rejecting other protocolsContent filtering – restricts access to content based on file

typeCaching – stores frequently accessed pages


Streaming Audio and VideoAllows a media player (or plug-in) to start playing multimedia

content while data is still being receivedCan broadcast live audio/video feeds or serve prerecorded

clipsWeb browsers employ a plug-in to view any type of streaming

contentUnlike HTTP, many streaming media formats may use User

Data Protocol (UDP) instead of TCP/IP as a network protocolUDP is good for transmitting very small pieces of data quicklyUDP will not retransmit data if there is an errorUDP is faster than TCP/IP although TCP/IP is more reliable


File Transfer Protocol (FTP)Used to transfer files between computers on a

networkRelies on client and server software, unlike HTTPFTP daemon (FTPD) runs on the server to allow

clients to connectIt provides a means of authentication for only authorized

users to transfer filesUNIX servers generally install an FTPD by default


Server-Side ProgrammingServer-side programs provide dynamic content and

allows interaction with users using:PerlActive Server Pages (ASP)ASP.NETJava Server Pages (JSP) and Java ServletsPHP: Hypertext Preprocessor (PHP)Coldfusion


DatabasesDatabase – a collection of data and metadata about related

entitiesA large corporate database should typically be installed on its own

dedicated server and not on a Web server machineMetadata – data about other data

Database management system (DBMS) – software that is used to manipulate a database Structured Query Language (SQL) – language built in relational DBMSs to

create and manipulate databases E.g. of relational DBMSs include Oracle, MySQL, Microsoft SQL Server,

Microsoft Access etc


Secure Socket Layer (SSL)A protocol that allows secure, encrypted

communication over TCP/IPOften used with HTTP to allow information exchange

between a Web browser and a Web serverMost commercial Web server software includes an

SSL server that can run alongside the HTTP daemon (HTTPD)

An Internet socket is defined as a combination of an IP address, a port, and a protocol


2440: 141 Web Site Administration Web Application Resources Instructor: Enoch E. Damson.

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Transcript of 2440: 141 Web Site Administration Web Application Resources Instructor: Enoch E. Damson.