Accessing a database

Accessing a database

An application server lets you work with server-side resources such as databases. For example, a dynamic page may instruct the application server to extract data from a database and insert it into the page’s HTML. For more information, see Beginner’s Guide to Databases in Using Dreamweaver.

The instruction to extract data from a database is called a database query. A query consists of search criteria expressed in a database language called SQL (Structured Query Language). The SQL query is written into the page’s server-side scripts or tags.

An application server cannot communicate directly with a database because the database’s proprietary format renders the data undecipherable in much the same way that a Microsoft Word document opened in Notepad or BBEdit may be undecipherable. The application server can communicate with the database only through the intermediary of a database driver: software that acts like an interpreter between the application server and the database.

After the driver establishes communication, the query is executed against the database and a recordset is created. A recordset is a set of data extracted from one or more tables in a database. The recordset is returned to the application server, which uses the data to complete the page.

Here’s a simple database query written in SQL:

SELECT lastname, firstname, fitpoints
FROM employees

This statement creates a three-column recordset and fills it with rows containing the last name, first name, and fitness points of all employees in the database. For more information, see SQL Primer in Using Dreamweaver.

Here’s an illustration of the process of querying a database and returning data to the browser:

This image shows how the web server interacts with a database when a dynamic page is requested.

You can use almost any database with your web application, as long as the appropriate database driver for it is installed on the server.

If you plan to build small low-cost applications, you can use a file-based database, such as one created in Microsoft Access. If you plan to build robust, business-critical applications, you can use a server-based database, such as one created in Microsoft SQL Server, Oracle 9i, or MySQL.

If your database is located on a system other than your web server, make sure you have a fast connection between the two systems so that your web application can operate quickly and efficiently.



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Dreamweaver Basics
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