Components of a Database-based applications on the Web
1. Browser
The browser is client for Database-based applications on the Web. Its responsibilities mainly are rendering (layout and display) of HTML and execution of client-side extension functionality such as JavaScript, ActiveX, and Java applet.
A large variety of browsers the developers have to deal with, each of them has its own advantages. In order to develop application on the Web, it is usually hard for the developer to choose specific browsers. The developer has to consider which browsers can support the technology used and the likelihood of their usage by the users.
A comparison between two most widely used browsers
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Netscape Navigator |
Internet Explorer |
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Runs on numerous platforms |
Runs only on Microsoft operating systems |
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Support JavaScript, Java |
Support JavaScript (incomplete), Java, ActiveX, VBScript |
2. Application logic
The application logic obtains data for a query (a keyword, a SQL statement, etc), prepares and sends the query to the database via a connection piece, retrieves the results from the connection piece, and formats them for display. The developers have to spend most of the time for this component. This component can exist as a CGI program, server API program, server module, browser plug-in, or Java applet.
3. Database connectivity
This component provides a link between the application logic and the database management system. The solutions come in many forms:
Database API libraries.
Database API libraries are collections of functions or object classes that provide the source code an ability to access databases. It lies at the core of every Web database-based application and gateway. No matter how the application is built, whether by coding CGI programs or by using a visual application builder, database API libraries are the foundation of database access. These connection solutions offer direct, low-level access with little overhead. Examples of some solution products are Pro*C, oraperl, sybperl, DBI w/DBD::Oracle.
Native database APIs. Most databases offer their own APIs. Native database APIs are databases dependent and also platform dependent as well as programming language dependent but they are not dependent on the Web server.
Database-Independent APIs:ODBC. ODBC is an open database connection standard supported by almost all of the databases. It standardizes access to databases from multiple vendors. Any ODBC-based Web application requires a database-specific ODBC driver to be loaded on the database client machine.
Programs that themselves are database clients. such as sqlplus for Oracle, isql for Informix, misql for Illustra, etc.
Web/Database development tools
Tools that help developers to develop database-based applications on the Web can be categorized into many classes (Ju, 1997):
Template-driven packages
These tools usually consist of template containing nonstandard and HTML tags, a second server (in addition to the Web server) which parses the template, and database client daemons. Developing applications by using these packages is easy. The developer just creates a template using standard HTML and special tags. However, the template must be processed on demand and require heavy string manipulation. Moreover, using them is slow compared to using a direct access such as native database APIs. Complex manipulated-application may not be possible to be created by such a software package since they offer only a limited range of flexibility and customizability. Examples of these tools are Illustra and Informix�s Web Datablade, DB2�s Net.data, Sybase�s web.sql.
This solution actually uses database APIs and the supporting gateways such as CGI, Server API, but all this interactivity is hidden from the developers.
GUI Web database application builder
These tools generally include a user-friendly interface, allowing developers to build an application easily with a series of mouse clicks and some textual input. Various technologies are used such as ODBC, native database API libraries and still some use database net protocols. A building tool may generate a CGI program or Web server API program such as NSAPI or ISAPI. Main advantage of using visual building tools is that developers can rapidly develop and prototype without knowing the details of what is happening in the foundation layers. However, the result of the program depends on the package used. It may be slower to execute than a similar program coded by hand. Examples of these tools are Sapphire/Web, Net.Dynamics, etc.
Chosing the method depends on several factors. One factor to consider is the database platform you want to provide accesses. Another factor is the skill of the developer and also the cost of the access method to be used (Swank, et al.,1997).
4. Database ( or database management system)
This component is responsible for storing data, retrieving data based on user-defined queries, and handling varying levels of security of the housed data.
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