1. Lecture plan Information retrieval (from week 11)
Databases and the Web
Jane Reid, BSc/IT DB, QMUL, 25/3/02

2. 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

3. Web/DBMS integration 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

4. 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

5. 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

6. 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

7. 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

8. Java resources [2] Java Servlets Java Server Pages (JSPs)
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

9. 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

10. 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