Download Web Technology and DBMS

Web Technology and DBMS’s
(CB 29)
CPSC 356 Database Design
Ellen Walker
Hiram College
(Includes figures from Database Systems by Connolly & Begg, © Addison Wesley 2005)
What is the Internet?
• Interconnected Networks
– Interoperable via standards (TCP, IP)
• History
– ARPANet (late 60’s, early 70’s) - military
– NSF took over, provided funding (1986)
– Commercial backbones (1996 - present)
Internet vs. Intranet
• Internet
– Global, open, public
– Called “extranet” to distinguish from Intranet
• Intranet
– Private network for exclusive use of an
organization
– Behind a firewall
• Typically, limited interaction
Internet Evolution of a
Business (Cisco)
• E-mail
• Web site
• E-Commerce
– Customers can place and pay for orders via web
• E-Business
– Complete integration of Internet technology into
business’s infrastructure
• Ecosystem
– Entire business process automated - customers,
suppliers, alliance partners, corporate
infrastructure merged into seamless system
Web vs. Internet
• Internet provides infrastructure of
information transmission across the
network
• Web contains interlinked information
(web pages)
– Servers: contain pages and transmit on
request
– Clients (browsers): request and display
pages to users
Languages of the Web
• HTTP - protocol for sending / receiving web
pages. Includes GET vs. POST
• HTML - basic markup language (represents
complex pages as text). Includes mechanism
(href) to reference other pages.
• XML - extended markup language generalization of HTML to represent more
complex document information
• (etc) -- this is not a complete list!
Limitations of HTTP
• Each transaction consists of a single
request for data and a single response.
– GET = request data
– POST = response (or data from form)
• Protocol is “stateless” - does not retain
information beteween transactions
– Workarounds: cookies or hidden text
Static vs. Dynamic Web Page
• Static web page
– Contents of page stored in a file, served as
originally written
• Dynamic web page
– Generated as needed
– Only instructions for generating the page
are stored (e.g. php query/display based
on argument)
Dynamic Web Pages
• Input provided as parameters or from
forms in the page
• Data generated from queries
• Pages written in a “scripting language”
(PHP is one example)
Requirements for Web-DBMS
Integration
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Ability to maintain data security
Not tied to a single DBMS
Not tied to a single browser
Availability of all features of DBMS
Open-architecture approach, supporting
multiple servers, standard interoperability
languages (e.g. DCOM, CORBA, XML,
SOAP)
Advantages of Web Approach
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Simplicity
Platform independence
Graphical User Interface
Standardization
Transparent network access
Simplified deployment
Global access
Disadvantages
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(lack of) Reliability
(lack of) Security
Cost (!)
Heavy (unpredictable) loads
HTML limitations
Bandwidth & Performance limitations
Immaturity of platform & tools
Tools to Integrate the Web
• Scripting Languages
– Client-side or Server-side
• Common Gateway Interface (CGI)
– Server-side
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Web server extensions
Java, J2EE, SQLJ, etc.
Microsoft .Net
Oracle’s Internet platform
Scripting languages
• Programs embedded in HTML files on
server
• Behavior of all clients changed by
changing script on server
• Scripts are generally interpreted, not
compiled
JavaScript
• Server-side or Client-side (client-side
more common)
• Allows immediate reaction to user
interface widgets
• Object-based (Document Object Model)
• Limited relative to Java
• (VBScript : Visual Basic = JavaScript :
Java)
Perl, PHP
• Server side languages
• Heavy Unix flavor (e.g. use of regular
expressions)
• PHP preferred for Linux
– Integrates with Apache HTTP Server
– Works well with MySQL or PostgreSQL
Common Gateway Interface
(CGI)
• Defines how scripts communicate with web
servers
– Uses Environment variables, standard I/O on
server side
– Uses HTML Forms on client side (original impetus
for forms)
• Nearly any programming language can run
on server (std. output returned to browser)
• Server runs script based on filename (x.cgi,
x.php, etc) - this is configurable
CGI Environment
Advantages of CGI
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Standardized interface
Programming-language independent
Web-server independence
Simplicity
Wide acceptance
Disadvantages of CGI
• Web server can be bottleneck
• Problems from HTTP Statelessness
– No validation of user input (must go “back” to
repopulate form)
– No transactions (must connect to database on
every page)
• Security risks
– Scripts with greater privileges than server
– Risk of unanticipated (or malicious) user input
HTTP Cookies
• Stored by browser in a file on client
• Cookies set / retrieved by HTTP request
• Issues:
– Not supported by all browsers
– For privacy reasons, users disable cookies
Non-CGI Gateways
• API Extensions to server (NSAPI,
ISAPI)
• Scripts loaded as part of server
– Direct interaction with back end
– One copy per server, not per request
– Changes server executable (risk?)
• Requires specialized programmers
Vendor Specific Scripting
• Developed by vendors as server add-ons
– JSP - Java Server pages (Sun)
– ASP - Active Server pages (Microsoft)
• Flexibility of CGI, without performance
overhead and I/O limitations
• Better integration with vendor’s other web
solutions
• Some compatibility limitations
Sun’s Java Platform
• Java language: “write once run
anywhere”
• Assorted “editions”
– ME (embedded)
– SE (standard) - for desktop & workstation
– EE (enterprise) - for multi-tier, robust,
multiuser applications
Java 2 Platform (1999)
Microsoft .NET Platform
• Integrated across servers, OS, applications,
programming language environments
• OLE - Object Linking and Embedding
– Shared objects that provide specific functionality
(e.g. sound clip)
• [D]COM([Distributed] Component Object
Model)
– Connects client application and object (binarycompatible components)
MS OLE - DB
.NET Framework
Oracle’s Approach
• Aimed at distributed environments
• N-tier architecture, based on industry
standards
• Designed for e-business
• Components include:
– TopLink (relate Java objects to relational
databases)
– Portal (entry point for web access)
– Business Intelligence (Reports, Discoverer, etc)
Oracle Internet Platform