Client/Server Model
RDBMS runs as a client/server model. Client can send ‘request’ to server and server returns ‘response’ to the request.
The following is an example of client/server model of web system. A client sends a request about web page reading, and a web server returns HTML file.
In RDBMS, user authorization step is added before request. As RDBMS can limit access to DB according to the users, a client should pass through authorization (e.g. ID and PW) first. After the authorization, a client can send a request.
Structure of Web Application
If the webpage is only composed of static HTML, a web server is enough. However, to generate HTML dynamically, we need control program. In web server, there is an extension for dynamic contents called CGI. The following is a structure of using CGI in web.
In database field, CGI becomes a client for database. Focus on the right part of the image below. After authorization to access, CGI delivers SQL requests to DB and DB returns responses to CGI.
MySQL
In MySQL, a client and a server runs in the same computer. As we still need network connection, client pass through network and access to server, which is called ‘loop back’ access.
All images, except those with separate source indications, are excerpted from lecture materials.
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