Database Management System

A database management system is a program, or collection of programs, that allows any number of users to access and modify the data in a database. Many different DBMS programs are available. Enterprise-level products, such as Oracle, DB2, and Sybase, are designed to manage large corporate or special-purpose database systems. Programs such as Microsoft Access, Corel's Paradox, and Lotus Approach are popular among individual and small-business database users.

The DBMS interface presents the user with data and the tools required to work with the data. Data management functions include: creating tables, entering and editing data, viewing data, sorting records, querying the database, generating reports.

To create a new database, you must first determine what kind of data will be stored in each table. In other words, you must define the table's fields with a three-step process: name the field, specify the field type, specify the field size. Most modern database systems can work with seven predefined field types: text fields, numeric fields, date fields, logical fields (called Boolean fields), binary fields, counter fields (sometimes called autonumber fields) and memo fields (also called description fields).

After the table has been set up, data can be entered. In most cases, entering data is a matter of typing characters at the keyboard. Most DBMSs allow you to create a data entry form to make data entry easier.

Sometimes viewing the entire table is unwieldy because there are too many entries. For displaying a selected list or subset of records from a table filters can be used. They tell the DBMS to display those records that satisfy the condition while hiding – or filtering out – those that do not.

One of the most powerful features of a DBMS is the ability to sort a table of data, either for a printed report or for display on the screen. Sorting arranges records according to the contents of one or more fields. For example, in a table of products, you can sort records into numerical order by product name or into alphabetical order by product name.

You can enter expressions or criteria that allow the DBMS to locate records, establish relationships or links between tables to update records, list a subset of records, perform calculations, delete obsolete records, perform other data management tasks. Any of these types of requests is called a query, a user-constructed statement that describes data and sets criteria so that the DBMS can gather the relevant data and construct specific information. In the mid 1970s mainframe database developers created the Structured English QUEry Language (SEQUEL), and its later variant SQL. They are English-like query languages that allow the user to query a database without knowing much about the underlying database structure. In addition to SQL, PC-based databases sometimes use a query/programming language called Xbase.

Not all DBMS operations have to occur on screen. Just as forms can be based on queries, so can reports. A report is printed information that, like a query result, is assembled by gathering data based on user-supplied criteria. In fact, report generators in most DBMSs create reports from queries.

Date: 2015-12-11; view: 919