General web based structure to access the database through ASP pages.
Three tier client server model used in various projects
A Client-Server application was originally designed to be a two-tier application. Client side (top tier) of the application consisted of front end and business logic. Server side (second tier) consisted of database to store useful data. At a given time, there were several clients connected to the database. Synchronization between these clients was provided through the database.
Recently, most of the Client-Server applications have been exported to the Internet. Internet Client-Server applications are inherently three tier systems. Three-tier Client-Server model consists of a very thin layer of HTML, a fat layer of CGI and bottom layer of database. The HTML layer deals with the presentation logic. Based on Business logic, the CGI layer filters out the data and gives it to presentation layer. The CGI layer receives data from database layer. Synchronization between several clients is provided through the CGI layer and results in reducing the load on the database.
Currently developers are faced with following problems.
- Which programming languages (e.g. HTML, Java Applet or ActiveX Control) to choose for presentation layer.
- Which programming languages (e.g. Java or C++) to choose for CGI layer.
- Which distributed protocols (e.g. COM, CORBA, TCP/IP, HTTP) to choose to communicate between these layers.
- No design patterns for developing reusable objects (like Customer, Employee), which could be used in two-tier vs. three-tier applications, COM vs. CORBA
