Databases and the Web

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Databases and the Web
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Client-Server Architecture

• In a File-Server client architecture each client
  must run a copy of the DBMS
• A better solution is to have a central database
  server which performs all database commands sent
  to it from client PCs.
• Application programs on each client PC can then
  concentrate on user interface functions.
• Database recovery, security and concurrency
  control is managed centrally on the server.

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Client-Server Architecture

• DATABASE SERVER
• The SERVER portion of the client/server database
  system provides processing and shared access
  functions.

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Client-Server Architecture

• CLIENT
• Manages the user interface (controls the PC
  screen, interprets data sent to it by the server
  and displays the results of database queries)
• The client forms queries in a specified language
  (usually SQL) to retrieve data from the database.
  This query process is usually transparent to the
  user.

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Client-Server Architecture

• ADVANTAGES
• Allows companies to harness the benefits of
  microcomputer technology such as low cost.
• Processing can be performed close to the source
  of the data - more speed.
• Allows the use of GUI interfaces that are
  commonly available on PCs and workstations.
• Paves the way for truly open systems.

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Client-Server Architecture

• DESIGN ISSUES 1
• The server must be upgradeable to allow for the
  growth in clients.
• The server must have capabilities for backup,
  recovery, security and UPS.

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Client-Server Architecture

• DESIGN ISSUES 2
• Can be complex and so requires specialised and
  expensive tools such as database servers and
  APIs.
• A lack of comprehensive standards.

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Traditional Client-Server Architecture

• Traditional Database Systems are based on a
  two-tier client-server architecture
• Fat clients

• User interface
• Main business and data processing logic

Client
Database Server

• Server-side validation
• Database access

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Web Architecture

• Need for enterprise scalability causes problems
  which can be solved by a three-tier architecture
• Thin clients

• User interface

Client
Application Server

• Business logic
• Data processing logic

• Server-side validation
• Database access

Database Server
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Web as a Database Platform

• Advantages
• DBMS advantages, e.g. transaction control,
  concurrency control, security, integrity
• HTML easy to use, standardised, cross-platform
  support
• Graphical User Interface simplify and improve
  access to database
• Transparent network access URLs
• Scalable deployment no need to update clients
• Innovation globally accessible

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Web Database Approaches

• Traditional web pages are normally static
• To run queries, we need to be able to produce
  dynamic HTML pages
• Approaches include
• CGI - Common Gateway Interface (with PERL etc)
• JavaScript - code which runs on client machine
• PHP - Server side processing
• Active Server Pages - MS variation of PHP

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Simple Page Request
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PHP Request
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PHP/Oracle Request
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Example PHP code

• ltHTMLgt
• ltHEADgtltTITLEgtPHP Exercise 1lt/TITLEgt
• lt/HEADgt
• ltBODYgt
• lt?php
• echo "Hello php world"
• ?gt
• lt/BODYgt
• lt/HTMLgt

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Example HTML code

• lthtmlgt
• ltHEADgtltTitlegtPHP Exercise 2lt/titlegt
• lt/headgt
• ltbodygt
• lth2gtltcentergtEnter the details belowlt/centergtlt/h2gt
• ltbrgt
• ltform method"post" action"phpex3.php"gt
• Enter your Userid
• ltinput type"text" name"usid"gtlt/inputgtltbrgt
• Enter your password
• ltinput type"password" name"passw"gtlt/inputgtltbrgt
• ltinput type"submit" name"submit"
  value"click"gtlt/inputgt
• lt/formgt
• lt/bodygt
• lt/htmlgt

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Example PHP code

• lthtmlgt
• ltheadgtlttitlegtPHP Exercise 3lt/titlegt
• lt/headgt
• ltbodygt
• lt?php
• Check that input has been made in userid field
• testin1 substr(usid,0,1)
• testin2 substr(passw,0,1)
• if (testin1 "")
• print "lthrgtlth1gtNo Name Entered -- Go Back To
  Previous Pagelt/h1gtlthrgt"
• elseif (testin2 "")
• print "lthrgtlth1gtNo Password Entered -- Go Back To
  Previous Pagelt/h1gtlthrgt"
• else
• echo "Welcome usid to the world of PHPltbrgt"
• ?gt
• lta href"phpex2.html"gtReturnlt/agt

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Useful Sources

• Client-Server
• Connolly Begg, 3rd and 4th edition, chapter 2
• Databases and the web
• http//www.php.net
• Connolly Begg, 3rd edition, chapter 28
• Connolly Begg, 4th edition, chapter 29
• Next week
• Revision