For the purposes of this chapter, an application server is any middleware through which clients go to get data. The application server can be as complex as an Enterprise JavaBeans application server or as simple as a web server pulling dynamic content from MySQL. The application server is generally the piece of your application that will perform user management. It is also the final arbiter of who can access what system resources available to the application.
User management is a very complex topic on its own. Not only does it cover how you store users, but it covers such topics as biometric authentication and digital certificates. All of that is well beyond the scope of a book on MySQL. We will take a look at simple user management as an example of how an application server can manage its users without making MySQL handle users in its security scheme.
To manage users, you need a place to store them. There are two common choices:
A directory server
Some applications even store their user information in files on a server. The flat file approach, however, is very risky and hard to maintain.
A directory server is a database that stores its data hierarchically. Instead of structuring data in tables with foreign key relationships such as a relational database, a directory service stores data in a tree. This structure is useful for data that naturally fits into a hierarchical structure. User data often, but not always, fits well into this ...