clarke, r. j (2001) l213-06: 1 multimedia in organisations buss 213 lecture 11 delivery approaches:...

Clarke, R. J (2001) L213-06: 1

Multimedia in Organisations

BUSS 213

Lecture 11Delivery Approaches:

Magnetic/Optical; Internet and Hybrid

Clarke, R. J (2001) L213-06: 2

Notices General

Marking is not complete for Assignment 2- should be available Tuesday this coming week

Will student 2147816 see Dr. L. Schafe concerning Assignment 2

Students must be allocated to A3 Groups today- make sure I know which group you are in

this week we will discuss storyboarding in tutorials- you will work on assignment

BUSS213 website where you can find out the latest Notices and get Lecture Notes, Tutorial Sheets, Assignments etc is:

www.uow.edu.au/~rclarke/buss213/buss213.htm

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Agenda (1)

in this lecture we examine modes of delivery for multimedia in this lecture

so far in this course we have assumed that multimedia systems are delivered to users by means of magnetic/optical storage (primarily CD-ROMs)

however in this lecture we emphasise what is and will continue to be arguably the most common form of multimedia delivery- the Internet- and more particularly the WWW

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Agenda (2)

the Internet and WWW provides unique opportunities for multimedia developers as well as posing real problems- is is very complex requiring mastery of a large number of disparate technologies server-side and client side

the web provides the possibility of having some content especially in the form of text resources updatable over time

unfortunately video and other resource intensive temporal media don’t work well over the net

this has resulted in the development of web-based or so-called hybrid multimedia systems in which users have CD-ROMs full of video content, indexed by web pages served across the internet

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Agenda (3)

I consider hybrid multimedia systems to be no different to other web applications but they have surprising effects on content

rather than thinking of the content in a multimedia system as static- we can think of content as a process- as evolving- this really does lend itself to the creation of organisational multimedia

Unlike the usual educational multimedia systems that are developed- we aren’t playing games any more!

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Agenda (4)

we describe web technology especially: web clients and servershow servers actually serve up pageswhat other operations they performthe concept of web applicationsthe concept of dynamic websites

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Related Readings

Vaughan (1998) Chapter 18: Designing for the World Wide Web, 495-520

Vaughan (1998) Chapter 20: Delivering, 543-568

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Web Clients & ServersSource: Yeager & McGrath (1996, 11-16)

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Internet

Internet (=Internetworking) collection of computer networks and to allow interoperability between them

networks can consist of many types of network technologies, protocols, and computers

Several protocols are required for transmitting data across the Internet (TCP/IP)

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InternetInternet Protocol

IP manages the transfer of data across physically distinct networks

transfers data into packets within an ‘envelope’ that describing its source and destination

a message is in effect shattered into pieces, packaged as packets in envelopes, and burst transmitted to the destination

IP looks after delivering these packages- one packet at a time!

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InternetTransmission Control Protocol

networks are unreliable and IP does not guarantee that all pieces arrive (no notion of a connection)

TCP defines conventions that make sure the pieces arrive in the correct order- by specifying another envelope around the data packets

IP layer moves packets, TCP manages the connection

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InternetOther Services & Protocols

the layering or encapsulation which is a characteristic of OSI also works in much the same way with other services supported by the Internet (TCP/IP)

File Transfer Protocol defines the conventions which describe how computers can cooperate in order to copy files from one computer to another on the Internet- it uses TCP/IP to do this

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InternetOther Services & Protocols

Physical Network

Internet Protocol; Transmission Control Protocol; File Transfer Protocol

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InternetWeb Services & Protocols

the web is just another internet service!Hypertext Transfer Protocol (HTTP) is the

set of rules for making and fulfilling web requests

however, the web is also designed to encapsulate other protocols including FTP, Gopher, WAIS, telnet and NNTP- we will talk about these services latter

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InternetWeb Services

works as a client-server- in terms of services not necessarily hardware

differs from other network models (terminal to mainframe; and peer-to-peer) because client and server are independent, fully functional computer systems in their own right

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InternetWeb Services

Mainframe & Terminal

Client-server

Peer-to-Peer

Typing

Printing

Request

Send Message

Send Messageemail

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Intranets & OASuccess of WWW- Open Standards

machines on the Internet are effectively decentralised

an important aspect of the web is that it is a set of open (not proprietary) protocols:Uniform Resource Locators URLs Hypertext Transfer Protocol (HTTP) Hypertext Markup Language (HTML)

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Intranets & OASuccess of WWW- Specific Issues

web protocols are general enough to be implemented on any computerweb application are the ‘topmost’ layer

in the Internet protocol hierarchycomplex processes of transfer of data

are ‘hidden’ from the web application developer and user

as a consequence there is a great variety of web applications available

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Web Servers & ClientsSource: Yeager & McGrath (1996, 11-16)

Physical Network

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Serving Documents- Example

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Serving Documents- Example 1: Server waits for a new request

httpd program waits for a clients request to arrive from somewhere on the Internet

server listens to a port until someone calls it and until that occurs it is dormant

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Serving Documents- Example2: Request arrives from client ...

ultimately a request is sent by a client to the server either by typing a URL or selecting a HTML anchor

the network software (client) locates the server computer and sets up a 2-way network connection from the client to the server

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Serving Documents- Example... 2: Request arrives from client

client can locate servers by the use of Internet protocols and the name service (DNS) to locate and initiate a connection with the server

once the connection is established the client sends the HTTP request:

GET /sample.htm HTTP/1.0

sent over the network in ASCII, server receives it and saves it

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Serving Documents- Example3: server parses the request ...

server decodes the request using HTTP protocol to determine what to do

there are three important pieces of information:the method instructs the server as to

what action should be taken. The GET method is used to locate and read the file and return it to the client ...

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Serving Documents- Example... 3: server parses the request

the document (/sample.htm) can be fetched by the server because it knows where it is in the document tree, and the

browser protocol being used (HTTP/1.0) so that the contents can eventually be returned to the client sent back over the same connection as the request. (Note that the server need not find the client on the Internet or make a new connection)

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Serving Documents- Example4: Read other information (if necessary) ...

the httpd program reads the rest of the requests needed

using HTTP/1.0 the browser is expected to send additional information about itself to the server

this meta-information describes the browser and its capabilities which may be needed by the server to reply to the request

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Serving Documents- Example... 4: Read other information (if necessary)

for example:User-agent: Mosaic for X Windows/2.4Accept: text/plainAccept text/htmlAccept: image/*

indicates the browser is Mosaic configured to display text, and any kind of image

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Serving Documents- Example5: Do the requested method ...

Assuming no errors, the httpd program executes the request

to GET a document requires looking up the file /sample.htm in its document tree using its standard operating system

there are two alternative courses of action depending on sucess or failure

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Serving Documents- Example... 5: Do the requested method (Success) ...

the httpd daemon sends a result code and the information that describes the type of information expected by the clientas the document is found a code 200

(everything is OK) is sent and the document will follow

the information is a HTML document so the Content-type: text/htm; the document is 1066 bytes long so the Content-length: 1066

the server software and the file date are also included

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Serving Documents- Example... 5: Do the requested method (Success)

the header sent to the client might look something like this:

HTTP/1.0 200 Document followsServer: NCSA/1.4Date: Thu, 20 Jul 1996 22:00:00 GMTContent-type: text/htmlContent-length: 1066Last-modified: Thu, 20 Jul 1996 20:38:40 GMT

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Serving Documents- Example5: Do the requested method (Failure)...

if the requested file could not be found or read then the status code will not be 200

the most common problem is that the name of the requested file is misspelt so the server cannot find it

if the requested file was called smple.htm it would not be found- the server would send a status code 403

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Serving Documents- Example... 5: Do the requested method (Failure)...

the response might look like this:HTTP/1.0 403 Not Found

Server: NCSA/1.4

Date: Thu, 20 Jul 1996 22:00:00 GMT

Content-type: text/htm

Content-length: 0

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Serving Documents- Example6: Finish Up

when the file is completely sent or an error message is sent, the httpd server has finished its work- it closes the

file if it was open, and closes the network port which terminates the network connection

the client receives and formats the data- the server knows nothing

the httpd server listens for another request (go back to step 1)

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Web Server Operations

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Web Server Operations

a web server has a collection of information in a document tree and it serves it according to the HTTP protocol

web servers are reactive programs waiting until a request is made; it attempts to make it, this is repeated etc.

the previous example is only slightly simplified

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Web Server OperationsHandling Multiple Requests (1)

if a server processes one request at a time, but can receive many simultaneous requests then delays will occur- an image may take several seconds to serve without a priority scheme, small jobs that can

be serviced quickly take inordinate amount of time to serve

with a large number of hits servers can go down- backlog can be too great

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Web Server OperationsHandling Multiple Requests (2)

web servers are therefore designed to handle as many requests as possible simultaneously

several strategies are available to do this (the last two are are more difficult unless special software is used): clone a copy of the httpd program for each

request- very easy under UNIX multithreading the httpd program spreading the work amongst several helper

programs

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Web Server OperationsCloning Servers (1)

each request is processed by a new copy of the httpd program

the original server called the parent immediately returns to listening for another request

the new copy called the child performs the processing

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Web Server OperationsCloning Servers (2)

the parent passes the network connection to the adult at the time that it is first spawned

when the has services the request, it terminates forever

the web server hardware may have many copies of the httpd program running simultaneously

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Web Server OperationsMultithreaded Execution

many mechanisms can be used for implementing this approach server may monitor the progress of several

connections, switching between them as necessary

when a lengthy process is in operation the server may switch to another pending task

when the pending processes is complete it can return to the previous lengthy process

server closes the network connections of any finished processes

this can be an extremely efficient method

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Web Server OperationsServers as Cooperating Sets of Programs

the httpd server itself can be made a set of cooperating programs specialised to perform particular tasks

One program reads the requests fro the network, another allocates them to specialised helper programs

the scheme is very efficient, the number of helpers can be adjusted to meet the number of requests, the type of requests (generally less common) or the size of the system

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Web Server OperationsMultiple Web Services on the same Servers

more than one web service can run on the same computer

any number of httpd programs can run on a UNIX machine as long as they have a unique port number the following web services are on the same computer

but different ports (the superuser sets up port 80 servers, but users can own and operate unrestricted ports above 1024):

http://www.rods.org/index.htm (port 80)http://www.rods.org:8080/index.htm (port 8080)http://www.rods.org:8081/index.htm (port 8081)

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Web Server OperationsEstablishing a Two-Way Network Connection

client must look up the network address of the server using its name

the client’s system software sends a packet back to the server, requesting a connection

the server’s system software sends a packet back to the client, agreeing to set up a connection

the client program is connected to the new network connection

the server program is connected to the new network connection

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Web Applications

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Web ApplicationsFrom Multimedia to Web

User Interface(BHP Project Director)

Version ControlSubsystem

Web Server (Apache)

Database Integration (PHP)

Database (MySQL)

Local (Client-side)front-end or client side may run as an apparently standalone application

Remote (Server-side)back-end may be a proxy or web server (local or remote) that allows updates for some resources

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Web Applications

a number of companies are implementing ‘mission-critical’ web based applications these applications generally utilise databases attempt at developing closer alliances with

customers, suppliers, partners, and employees organisational multimedia systems will

increasingly become delivered in this form by using heterogeneous platforms, multimedia

content is distributed throughout the infrastructure of a firm

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Web Applications

sophisticated web applications must support complex Internet/intranet system configurationsystems level hardware/software, and

networking products must work together

software elements: JAVA applets, Microsoft Active X controls, CGI scripts, SQL code

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Web ApplicationsWeb Database Applications- Components

External“helper”program

HTML Document

Javaapplet

JavaApplication

CGI program

ProprietaryWeb Server

Web ServerAPI module

Vendor’sDatabase API Command-line

interface to database

ODBC JDBC

BrowserLayer

ApplicationLogicLayer

DatabaseGatewayLayer

DatabaseLayer

Database (RDMS)

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Web ApplicationsSystem Configuration: Logical View

Firewall

Client Workstations with Web Browsers Production

Web Server

Application Server

DatabaseServer

MainframeDatabase

DevelopmentWeb Server

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Web Applications

all real system development is complex, and web applications are no different to traditional systems development projects in that respect

however they pose special challenges due to the fact that there are numerous technologies involves

web-based application components must be thoroughly tested to ensure that they are reliable, defect-free, and meets its original design purposes

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Web ApplicationsClient-side Components

Standard WindowsGUI Objects

Browser Specific Objects

Procedural Logic (Client or Server)

Special HTMLExtension Objects•tables•frames

NavigationalObjects•text links•image links•image map links

•display text•images•backgrounds•control buttons•edit fields•list boxes•radio buttons•checkboxes•cursor•pull-down menus•dialog boxes•forms

•Java Code•Javascripts•Active X controls•procedural logic coded with various proprietary scripting languages

Multimedia Objects

•audio streams•video streams•VRML plug-ins

NetObjects Support

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Web ApplicationsServer-side Components

Firewall

Application Server

Mainframe Database

•provides special purpose applications necessary to support a web application•generally invoked by passing a request from a CGI script

•Prevents unauthorised access to Intranet•Implements security policy and ‘stance’ for Web Applications

•Central repository for all data in the organisation•Database Server provides a view on the necessary subsets of this central repository data

Database Server

•provides database access for a web application•implemented using SQL commands•must support the database needs of a large number of potential users

NetObjects Support

Web Server

Production•Serves HTML/XML web pages•runs CGI scripts to provide added functions to web applications

Development•handles an internal representation of pages in a web application

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Web ApplicationsVarious Kinds of Testing

Client-side Testing Browser compatibility testing Desktop configuration testing Usability testing Documentation testing Security testing Error message testing Client load testing Cross-platform portability Applet/Script Testing GUI Testing

Server-side Testing Web-server Load testing Network Load Testing Application Server Testing Database Server Load

Testing

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Dynamic Websites

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Dynamic Websites

we have seen that organisational multimedia systems can be considered in the same way as other organisational web applications

multimedia content may be distributed across multiple servers-and served as required

there is still a major problem that faces conventional multimedia developers- although the content is now in principle able to be changed- this is difficult to undertake and so the multimedia site may suffer from the so called revision control problem also known as version control problems

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Static Site StructureFile System View

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Static Site StructureChanging Contents- Revision Control Issue

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Static Site StructureChanging Contents- Revision Control Issue…

Clicking on Aditya’s member link not only provides the content but a previous version of DSL website’s navigation frame

Static site structure easily creates situations where revision control errors like this can occur

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Static Site StructureChanging Contents- Revision Control Issue…

Clicking on Rodney’s member link provides content that is well-out-date

Static site structure easily creates situations where revision control errors like this can occur

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Static Site StructureLongitudinal Changes

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Content Theme

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Static Site StructureLongitudinal Change & Content Themes

different content themes (found as major global navigation options) are pictorially represented by the use of different coloured shapes along the x-axis

we can show changes to the site content over time (also called longitudinal change) along the y-axis

most web sites start out with well defined content t=0

Content Themet=0

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the site remains unaltered until the content is deemed to have a large number of errors in it

a review process is instigated and a new version for some of the content is created (t=1)

the next increments see the content changing in terms of its thematic classification (changes to colour) and its representation on the site (thickness)

Content Theme

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while all of the site will need to be reviewed not all of the content needs to be or can be changed (see boxed themes) t=2

sometimes the changes needing to be made represent an enormous burden as the site may need to be altered substantially t=3

this episodic, large scale updating websites is a major maintenance problem

Content Theme

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this episodic, large scale updating websites is a major maintenance problem

Content Theme

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this episodic, large scale updating of websites is a major maintenance problem

Content Theme

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Dynamic Website Dynamic Web Page Generation…

dynamic web applications are prevalent in commercial (e-commerce) sites, where the content displayed is generated from information accessed in a database or other external source a dynamic web page is a page that interacts with

the user, so that each user visiting the page sees customized information

both a web page's structure as well as its content can be customized- dynamic web page programming can produce web pages on-demand

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Dynamic Website No Material Presence

generally dynamic page generation is limited to specific small parts of the web

but there is a more radical alternative to having static or scalable web sites- one which has a great deal of promise commercially and in organisational multimedia systems

we can extend the idea of dynamic web pages to that of having dynamic web sites- sites that do not have a material presence until ‘requested’ as part of the user navigation clicking on links

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Dynamic WebsitesDescription and Rationale

develop dynamic site structure- sites that appear to the users to be dynamically change their structure to accommodate use

in fact when the user is navigating they are actually sending database queries and the web server generates the page on the fly

needed for organisations that are involved in time or priority ordering in tasks (event management or emergency services)

active area of research: modify systems network notation to include temporal logical develop a semantic theory of site evolution (has been done for

traditional IS)

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Dynamic Websites the structure of the web site

changes overtime, topics diverge and converge

weblets blur one into another overtime, as indicated by the gradual changes in colour

this change is driven by changes to types of requests being made over time- changes to the mission of the organisation and/or structural alterations to the communities that make up the organisation

Content Theme

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clarke, r. j (2001) l213-06: 1 multimedia in organisations buss 213 lecture 11 delivery approaches:...

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