3 Tier Web Development

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3 Tier Web Development

• Bryan Duggan

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Three important decisions

• Organisation
• Navigation
• Choice of technology

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Organisation

• How files are organised on the server
• By file type
• Separate folders for html, js, images
• By content
• Separate folders for sales, marketing, college

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Navigation

• Frames ?
• Site map
• Search on each page
• Drop down lists
• Search
• Long pages (links back to the top)
• Back functionality

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Choice of technology

• Client
• HTML/XHTML
• CSS
• Flash
• Javascript
• Java
• CSS
• Voice
• Middle tier
• PHP
• ASP
• JSP
• Cold fusion
• Server
• MySQL
• SQL Server
• Oracle

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Revision
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Question

• Place the following terms in the 3-tier
  architecture
• JavaScript, SSI, J2EE, MySQL, Oracle, CSS, PHP,
  ASP.NET, Flash, Java Applets, JSP, Dreamweaver,
  Microsoft .NET

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HTTP Protocol
RFCs 1945 2068 2616
Parameters
Request
Web Browser
Response
Query
E.g. A user fills in a form, which gets submitted
to a web server Port Numbers (16 bit numbers)
identify the service
Results
Web Server
Database (Optional)
http//www.ietf.org/rfc/rfc1945.txt?number1945
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Displaying a Web page in a Browser

• lta href http//www.cems.uwe.ac.uk/cjwallac/UFIE
  8V-2004/l2_3tier.htmlgtLecture 2lt/agt
• URL is decoded protocol/host/file
• Page requested from host
• Page is returned
• HTML codes determine how text is rendered
• If page contains links e.g. ltimg srcred.gifgt,
  browser must repeat the same process on each

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Dynamic Web page needed when

• Consistent look and feel on each page of a large
  site
• Data is derived from a database
• Depends on real time
• Pages depend on user choice
• Business transactions e.g. e-commerce

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Presentation tier

• Issue request to remote server
• accept the returned HTML (or JPEG..) file
• render (i.e. create a 2-d image ) the HTML
• allow plug-ins to handle new file types
• execute client-side scripts in JavaScript
• support interaction between client-side scripts
  and the web page
• accept user input via a variety of controls on a
  form

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Persistence tier

• interaction with the database using standard
  languages e.g SQL queries and table returns
• define and modify the data structures (e.g.
  tables) themselves ( the Database Schema)
• insert, update and delete data
• maintain data persistently, with backup and
  recovery
• handle transactions to support concurrent access
  to the database via locking et
• optimise access by compilation of queries,
  indexing, replication of tables etc.

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Application Layer

• accepting requests from the Presentation layer
• interpreting the requests according to business
  rules and past transactions from this client
• requesting the appropriate data from the
  Persistence layer
• computing derived data
• creating the HTML (or GIF, MIDI..) for the page
• providing run-time support for
• Thousands of concurrent users
• compilation to machine code
• multi-threading allow multiple processes to run
  concurrently
• caching holding results in a temporary store to
  reduce re-calculation

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LAMP Architecture
Linux
Parameters
Request
Mozilla/IE
Response
Query
Results
Apache /IIS Running PHP interpreter
HTTP
MySQL
Lynux, Apache, MySQL, PHP
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History of PHP

• PHP originally stood for Personal Home Page
• It started out, in 1994, as a simple preprocessor
  of HTML files
• built by Rasmus Lerdorf (born in Greenland, grew
  up in Denmark and Canada, graduated from U of
  Waterloo in 1993, now prominent member of Open
  Source movement)
• original purpose was to log people who viewed his
  on-line resume
• Since then, has been developed by a growing
  community of open source developers
• Name now supposed to stand for PHP Hypertext
  Pre-Processor

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PHP history (contd.)

• Initially, PHP comprised a simple parser plus a
  library of C functions
• The parser would scan a HTML file looking for
  instances of a new non-standard tag and replace
  the contents of these tag instances with the
  result of executing some functions in the C
  library
• As a result, much PHP syntax looks like C
• Other parts of it, however, have a Perl flavour
  but, of course, Perl also borrows C syntax

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Enabling PHP in HTTP servers

• PHP is available on many servers today, in
  Windows and all types of Unix environments
• It is supported by Apache, AOLServer, Roxen and
  others
• Servers can be configured to enable PHP in
  different ways
• The httpd recognizes a file who name has the
  suffix .php as a PHP file

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Installing PHP on Windows

• Install Apache web server (Accept the defaults)
• Install MySQL
• Optionally install the query browser and
  administrator
• Create a folder to hold your web documents
• C\Documents and Settings\bduggan\My
  Documents\Courses\Web Development
  (China)\Websites

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Install PHP

• Unzip to c/PHP
• Rename the file c\php\php.ini-dist to php.ini
• Edit the line doc-root to read
• doc_root C\Documents and Settings\bduggan\My
  Documents\Courses\Web Development
  (China)\Websites
• Edit the line extension-dir to read
• extension-dirc\php\ext
• Edit http.conf and change
• DocumentRoot "C/Documents and
  Settings/bduggan/My Documents/Courses/Web
  Development (China)/Websites
• Add
• ScriptAlias /php/ "c/php/"
• AddType application/x-httpd-php .php .php5
• Action application/x-httpd-php "/php/php-cgi.exe"
• SetEnv PHPRC "C/php

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Also Add

• This should be changed to whatever you set
  DocumentRoot to.
• ltDirectory "C/Documents and Settings/bduggan/My
  Documents/Courses/Web Development
  (China)/Websites"gt
• Possible values for the Options directive
  are "None", "All",
• or any combination of
• Indexes Includes FollowSymLinks
  SymLinksifOwnerMatch ExecCGI MultiViews
• Note that "MultiViews" must be named
  explicitly --- "Options All"
• doesn't give it to you.
• The Options directive is both complicated
  and important. Please see
• http//httpd.apache.org/docs/2.2/mod/core.ht
  mloptions
• for more information.
• Options Indexes FollowSymLinks

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Add

• ltDirectory "C/PHP"gt
• Possible values for the Options directive
  are "None", "All",
• or any combination of
• Indexes Includes FollowSymLinks
  SymLinksifOwnerMatch ExecCGI MultiViews
• Note that "MultiViews" must be named
  explicitly --- "Options All"
• doesn't give it to you.
• The Options directive is both complicated
  and important. Please see
• http//httpd.apache.org/docs/2.2/mod/core.ht
  mloptions
• for more information.
• Options Indexes FollowSymLinks
• AllowOverride controls what directives may
  be placed in .htaccess files.
• It can be "All", "None", or any combination
  of the keywords
• Options FileInfo AuthConfig Limit

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A first PHP file

• lthtmlgt
• ltheadgt
• lttitlegtPHP Testlt/titlegt
• lt/headgt
• ltbodygt
• lt?php echo ltpgtHello Worldlt/pgt" ?gt
• lt/bodygt
• lt/htmlgt
• Test this file and make sure PHP displays Hello
  World

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Optionall install phpMyAdmin

• This allows you to access MySQL in a web browser

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How PHP files are processed

• The httpd demon simply copies regular HTML
  content in the .php file to the message body that
  will be sent to a client which requests the .php
  file
• The new non-standard tag is of the form
• lt?php ?gt
• The text inside the tag is PHP code
• lt?php echo ltpgtHello Worldlt/pgt" ?gt
• The httpd demon executes this PHP code and copies
  the output text, generated by this PHP code, to
  the message body that will be sent to the client
• Thus, from the above, the client would see only
• ltpgtHello Worldlt/pgt

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Note following response

• Chunked transfer-encoding is used
• Because the httpd demon does not know, before
  executing the PHP content, how long the message
  body will be
• PHP code will been replaced, in the message body,
  by its output

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PHP files are not special

• PHP files do not have to be executable
• They can be regarded as simply HTML files with
  some new tags

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PHP tags

• In the example just seen, the PHP tag was
• lt?php ?gt
• This is the best PHP tag to use it is the one
  which works best if we are also using XML,
  because it avoids conflicts with XML Processing
  Instructions
• However, you may occassionally see the following
  tags being used in other peoples PHP code
• lt? ?gt
• lt gt
• ltscript languagephpgt lt/scriptgt