Databases and AOLserver

AOLserver can be configured to have access to multiple databases through AOLserver's database drivers. Currently, Illustra or SOLID database drivers are available. AOLserver creates a database pool, a group of connections to a database, for each database it accesses. See Chapter 3 for information on configuring AOLserver, and specifically the "Configuration for Multiple Database Pools" section for an example of configuring AOLserver for multiple Illustra and SOLID database pools.

AOLserver interacts with databases in the following ways:

• AOLserver dynamically generates search, entry, and update forms for tables in databases, which you can use as is or customize to suit your needs. See the "Automatic Forms Generation" section and the "Customize Entry, Update, and Search Forms" section for detailed information.

• You can create, extend, or delete tables in databases using a forms-based interface linked to the AOLserver administration page. You also have access to the automtatic search, entry, and update forms for the tables from this same interface. See the "Database Services in AOLserver" section for detailed information.

• AOLserver uses the Illustra database to support its full-text features: AutoLinking, indexing, and archiving. See Chapter 9 for more information.

• You can write your own Tcl or C extensions to access the database. See the Tcl Developer's Guide and the C Developer's Guide for more information.

What is a Database?

A database is a collection of data stored in a computer. A Database Management System (DBMS) is a software package that efficiently manages databases and lets one or more people use or modify the contents of the database. The main function of the DBMS is to manage the internal representation of the data in a form optimized for computer access, and to respond to requests from users to access or modify the data. The DBMS translates these requests into database commands that it then performs on the data.

One of the most common and powerful languages for accessing databases is SQL. SQL (Structured Query Language) commands perform actions on the database. There are two types of SQL commands: DDL (Data Definition Language) commands, which are used to define the structure of the data, and DML (Data Manipulation Language) commands, which are used to manipulate the data itself. The data is organized into tables in the database. Tables contain rows (sometimes called records) and columns (sometimes called fields). The structure of the table and its columns is defined by DDL commands. The commands to insert or update values in the rows of the table are DML commands.

AOLserver allows you to define the structure of the tables in your database, or manipulate the data in the database through a forms-based interface accessed through the Database Services link on the Administration page. AOLserver automatically translates the information in these forms into the appropriate DDL or DML commands and executes them.