INSE - Lecture 21 Web SE  Background (long to persuade you)  SE differences

Background to the Web  Overview of the history  Overview of the technology

How the Internet happened (1) First there were isolated mainframes –

How the Internet happened (2) Then there was some local linking –

How the Internet happened (3) Then national networks –

How the Internet happened (4) Then gateway-based inter-netting –

When the nets were joined  The various nets ’ protocols were merged –  POP2 and SMTP for mail  FTP for file transfer  IP/TCP as a low-level basis

Host “ Server ” programs … … are needed by most protocols:

Which all assumed …  that you already knew what internet resource you wanted, and where  i.e. that it existed, and it ’ s “ address ”  that the “ real ” work was done by standalone programs  which would be platform-dependant

“ Windows ” platforms … then became common  why not a “ windows ” program to “ look at ” suitably formatted files from elsewhere?  BROWSERS [late 1980s]

Using a Browser …

Main implications … 1) Mark-up language – HTML 2) “ Links ” from one file to another  we only need to know a “ start ” address into a web-site  searchers to find those start-points for us 3) HTTP protocol

But such files were “ dead ”  So why not add some programming capability to the HTML?  client-side?  server-side? [mid/late 1990s]

Client-side technology 1)Scripting, e.g. in JavaScript: for (I=0;I<10;I++) { … } document.write( “ ” ) 2)Applets (in Java), Flash, etc

Client-side capabilities  Scripts & Applets etc.  can read files from host  can write and read “ cookies ” locally on the client computer  can ’ t write files anywhere else

Server-side technology 1)Scripting, e.g. in PHP: <? for (I=0;I<10;I++) { … } echo “ to the client ” ; ?> 2)Servlets (in Java), JSP, ASP etc.

Server-side capabilities  Scripts + Servlets  can send HTML to the client/ browser  can read and write cookies on the client computer  can read and write files on the host computer  can invoke plug-ins of the server program – e.g. data-base engines

Inside the host+server

ENGINEERING web software  Implications of size & complexity on building large web-sites.  But first …

Small web-sites  Mostly “ one-man ” jobs  the one person does all the various kinds of work needed  a tradition of improvisation  little planning or design  a lot of “ evolving ” a site

Consequence:  Many badly-structures & poorly- built sites have failed  we seldom notice them (because they either disappear quickly or attract little use)

Then big/complex web-sites … … started getting built …  many of the problems we also get with big/complex non-web software  need to specify, design, plan, test, QA, etc.  BUT new kinds of problem as well.

Nature of a web application  Mix of  publishing  graphics, layout, etc.  interactivity  programming  advertising  commercial

Nature (technical view)  net-active  content-driven  “ look and feel ”  secure  continuous evolution  only the first release can be waterfall!  very quick/continuous developments

Consequences  Different sort of team  Different life-cycles  very quick evolution  new kinds of life-cycle stage  new elements in “ old ” stages  other new SE issues, other new PM-of-SE issues

Different sort of team  Content providers & developers  Artists, graphics designers, layout specialists  Tekkies! (us!)  “ Director ” to pull the parts together  “ Producer ” to manage the effort

New tekkie aspects (1)  Webmaster  often 2 levels:  Customer interface  Reporting customer issues – e.g. browser problems, navigation problems, bugs

New tekkie aspects (2)  Technical manager ensures  planning  oversight of development policies  ensures appropriate access rights/security  CM-like issues, including change control – but (1) fast (2) many small changes  QA including link monitoring (e.g. “ dead ” links)  site traffic measurement & analysis

New/changed lifecycle stages  Requirements (purpose?)  Spec (incl. content & art issues)  Design  architecture  navigation  interface  Content  conception  production  Testing – many new challenges  Customer evaluation

Project management issues  maybe slow initial build  then frantic continuous change  hard to plan  hard to control  very hard to ensure consistency  estimation – is it meaningful?

PM-of-SE issues (continued)  People –  very different kinds, mixed  much more than in a traditional SE team  crucial to have a “ team spirit ”  can ’ t afford internal politics

WEB SE – conclusion  All so familiar  All so different

After this lecture  Web SE is very new – so … … it will still change very fast for maybe another decade – so … … you ’ ll need to invest special effort to stay up-to-date with it

u © C Lester