Why Use a DBMS?

A question that is often asked is: why use a complex DBMS to manage data? There are several reasons that can be explained by contrasting a database with a spreadsheet, a simple text file, or a custom-built method of storing data. A few example situations where a DBMS should and should not be used are discussed later in this section.

Take spreadsheets as an example. Spreadsheet worksheets are typically designed for a specific application. If two users store names and addresses, they are likely to organize data in a different way-depending on their needs-and develop custom methods to move around and summarize the data. In this scheme, the program and the data aren't independent: moving a column might mean rewriting a macro or formula, while exchanging data between the two users' applications might be complex. In contrast, a DBMS and a database provide data-program independence, where the method for storing the data, the order of the stored information, and how the data is managed on disk are independent of the software that accesses it.

Managing complex relationships is difficult in a spreadsheet or text file. For example, consider our online winestore: if we want to store information about customers, we might allocate a few spreadsheet columns to store each customer's residential address. If we were to add business addresses and postal addresses, we'd need more columns and complex processing to, for example, process a mail-out to customers. If we want to store information about the purchases by our customers, the spreadsheet becomes wider still, and problems start to emerge. For example, it is difficult to determine the maximum number of columns needed to store orders and to design a method to process these for reporting.

Spreadsheets or text files don't work well when there are associations or relationships between stored data items. In contrast, DBMSs are designed to manage complex relational data. DBMSs are also a complete solution: if you use a DBMS, you don't need to design a custom spreadsheet or file solution. The methods that access the data-most often the query language SQL-are independent of how the data is physically stored and actually processed.

A DBMS usually permits multiuser transactions. Medium- and large-scale DBMSs include features that control the writing of data by multiple users in a methodical way. In contrast, a spreadsheet should be opened and written only by one user; if another user opens the spreadsheet, she won't see any updates being made at the same time by the first user. At best, a shared spreadsheet or text file permits very limited concurrent access.

An additional benefit of a DBMS is its speed. It isn't totally true to say that a database provides faster searching of data than a spreadsheet or a custom filesystem. In many cases, searching a spreadsheet or a special-purpose file might be perfectly acceptable, or even faster if it is designed carefully and the volume of data is small. However, for managing large amounts of related information, the underlying search structures in a DBMS can permit fast searching, and if information needs are complex, a DBMS should optimize the method of retrieving the data.

There are also other advantages of DBMSs, including data-oriented and user-oriented security, administration software, and data recovery support. A practical benefit is reduced application development time: the system is already built, it needs only data and queries to access the data.