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Lecture plan
• Information retrieval (from week 11)
• Databases and the Web
Jane Reid, BSc/IT DB,
QMUL, 25/3/02
1
Web/DBMS architecture
• 3-layer architecture:
– User interface layer (client)
• E.g. a Web browser
– Business logic and data processing layer (application server)
• E.g. a Web server
– DBMS (database server)
Jane Reid, BSc/IT DB,
QMUL, 25/3/02
2
Web/DBMS integration
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Scripting languages
Common Gateway Interface (CGI)
Web server extensions, e.g. API
Java resources, e.g. JDBC, Servlets, JavaServer Pages
(JSPs)
• HTTP cookies
• XML
Jane Reid, BSc/IT DB,
QMUL, 25/3/02
3
Scripting languages
• Script code is embedded in HTML, so is downloaded each
time the page is accessed
• Programs can be written with standard programming logic
– E.g. JavaScript includes Java-based functions and scripts to
respond to user input, page navigation, etc
– E.g. Perl combines features of C with some Unix utilities to create
and manipulate files, network sockets, database connectivity, etc
Jane Reid, BSc/IT DB,
QMUL, 25/3/02
4
Common Gateway Interface (CGI)
• A specification for transferring information between Web
servers and CGI programs using CGI scripts
• CGI scripts can be written in any language that supports
the reading and writing of an operating system’s
environment variables, e.g. Perl, Java, C
• Advantages are simplicity, language independence, Web
server independence, wide usage
• Disadvantage is that a new process is started up each time
a CGI script is invoked, which can be costly for the Web
server
Jane Reid, BSc/IT DB,
QMUL, 25/3/02
5
Web server extensions
• An alternative to CGI
• Non-CGI gateways , e.g. Application Programming
Interfaces (APIs), can be used to add functionality to the
Web server
• API provides a method for creating an interface between
the Web server and back-end applications using dynamic
linking or shared objects
• Advantages are improved functionality and performance
• Disadvantage is reliance on expert programming
Jane Reid, BSc/IT DB,
QMUL, 25/3/02
6
Java resources [1]
• Java offers a large set of resources to support Web/DBMS
integration
• JDBC
– Defines a database access API that supports basic SQL
functionality
– Java can be used as the host language for writing DB applications
– Higher-level APIs can be built on top, e.g. the JDBC-ODBC bridge
which provides JDBC access using ODBC drivers
• ODBC (Open DataBase Connectivity standard) provides a common
interface for accessing heterogeneous SQL DBs
• A single application can thus access different SQL DBMSs through a
common set of code IF the DBMSs are ODBC-compliant
Jane Reid, BSc/IT DB,
QMUL, 25/3/02
7
Java resources [2]
• Java Servlets
– Programs that run on a Java-enabled Web server and build Web
pages
– Analagous to CGI programming, but faster, portable, more
extensible, and more secure
• Java Server Pages (JSPs)
– A Java-based server-side scripting language that allows static
HTML to be mixed with dynamically-generated HTML
– Works with most Web servers, including Apache HTTP Server
Jane Reid, BSc/IT DB,
QMUL, 25/3/02
8
HTTP cookies
• A piece of information stored on the client on behalf of the
server
• Sent back to the server with each new client request
• Can be used to store registration information or
preferences
Jane Reid, BSc/IT DB,
QMUL, 25/3/02
9
XML
• Meta-language that enables designers to create their own
customised tags to provide functionality not available with
HTML
• A restricted version of SGML (Standardised Generalised
Markup Language), which itself is too complex for general
use
• Advantages are simplicity, platform-independence /
vendor-independence and extensibility
Jane Reid, BSc/IT DB,
QMUL, 25/3/02
10