What is a database?

A database is simply an organised set of information. Strictly speaking, there's no need for it to even be in computerised form - address books are often used as a simple example of a database, since they contain large volumes of information organised into categories (name, address, and phone number). Despite this, most people now take the term 'database' to refer to information stored electronically.

Note also that the general definition of a database given here could encompass many common PC applications, such as electronic mail (which can be organised by recipient or sender) or information in a spreadsheet (which tends to be structured mathematically). In practice, the term 'database' is most commonly used to refer to highly structured information (examples might include order forms or medical information). Most business databases will contain a carefully planned set of information that can be analysed to indicate overall trends, as well as providing a historical record of past transactions and activities.

A basic database system simply allows you to enter and search for information (a process often known as querying). Most modern databases also support the development of specific applications that run on top of the database, which enable you to access the features you need without having to worry about all the complexities of the system. For instance, within one company general staff might have access to an order entry system, while financial staff have access to automatic reporting systems that provide sales summaries and other information. Both use a database server to store information, but the means of entering this, and the ability to change it after entry, will vary between the different applications.

What is a database server?

A single-person business could run database software on just one PC quite easily. However, in most businesses data will need to be accessed by multiple staff across a network, often simultaneously. Database server software handles this task, making databases available to all relevant employees. This is not simply a matter of creating network connections. Database server software must ensure that information isn't modified by multiple staff members at once, index and sort the information that is entered so it can be easily searched, and allow analysis of the information stored in the database to produce reports. It also allows different applications to use the same centralised storage mechanism. With appropriate hardware, a database server can handle as many of these options as are needed. Staff may use different applications to access this information, but the server will handle the core data storage. Since databases were one of the earliest computer applications to be developed, they have become highly sophisticated over the years. Modern database servers can handle huge volumes of information and present it in a variety of formats, including automatically outputting Web pages from stored data and allowing the placing of orders and other electronic commerce tasks. For many businesses, a database server in some form will lie at the heart of most daily activities. A note about the word server is in order here. Database server software is distinct both from server hardware (which is the physical machine or machines used to run a network) and the server operating system (which runs on the server hardware and provides an interface between it and specific applications, of which a database server is one example). Despite this distinction, in practice all three will work together closely, and your choice of database server will influence your server OS and hardware choices.

	Microsoft's SQL server (which they arrogantly call " SQL Server ", as if theirs were the only one, or the original) is an example of Microsoft's efforts to take a standard (such as Structured Query Language) and add proprietary "extensions" that lock you into using their product. What's more, it's only available for Windows Server, so you can't run it on a less expensive, more stable platform like Linux or one of the BSD Unixes, or a the much more scalable commercial Unixes. Lately it's been an ongoing security problem, with a variety of known exploits active on the internet.
	MySQL is an incredibly popular free , open-source database server, largely due to the fact that it can typically run circles around the others , and runs efficiently with fewer resources . It does this at the expense of certain features, such as transactions and foreign keys, which makes it less suitable for certain kinds of applications, but if you don't need those features (and for things like publishing data on the web, you generally don't), it's a solid choice
	PostgreSQL is a very popular and highly-acclaimed free , open-source database server, and is often selected over commercial products... for its performance and features , not for its price. It's been in development since 1985; the fully-SQL-compliant version came out in 1995. It runs primarily on Unix-like systems, but an NT version is also available