Encyclopedia of Computer Science and Technology

database management system 131mentation of onsite and offsite backups and procedures forrestoring data (see backup and archive systems).System DevelopmentAn enterprise database is not a static entity. The demand fornew views or applications of data requires the developmentand testing of new queries and reports. While this is normallydone by the database programmers, the administratormay need to consider its impact on the operation of thesystem. The administrator also helps plan for the needs of agrowing, changing, organization by designing or evaluatingproposals for expanding the system, possibly moving it tonew hardware or a new operating system or migrating thedatabase applications to a new database management system(DBMS).Because of the importance of database management tocorporations, government, and other organizations, databaseadministration became a “hot” employment area inthe 1990s. Most database administrators specialize in aparticular database platform, such as Oracle or MicrosoftAccess. The growing need to make databases accessible viathe Internet has added a new range of challenges to thedatabase administrator, including the management of servers,remote authentication of users, and the mastery of Java,Common Gateway Interface (CGI), and scripting languagesin order to tie the database to the server and user (see Java,cgi, Perl, and xml).Further ReadingAbout.com. Database Administration [links]. Available online. URL:http://databases.about.com/od/administration/Database_Administration.htm. Accessed July 8, 2007.Alapati, Sam R. Expert Oracle Database 10g Administration. Berkeley,Calif.: Apress, 2005.Mannino, Michael A. Database Design, Application Development,and Administration. 3rd ed. New York: McGraw-Hill, 2005.Mullins, Craig S. Database Administration: The Complete Guide toPractices and Procedures. Reading, Mass: Addison-Wesley Professional,2002.MySQL AB. MySQL Administrator’s Guide and Language Reference.Indianapolis: MySQL Press, 2005.Wood, Dan, Chris Leiter, and Paul Turley. Beginning SQL Server2005 Administration. Indianapolis: Wrox, 2006.database management system (DBMS)A database management system consists of a database (acollection of information, usually organized into recordswith component fields) and facilities for adding, updating,retrieving, manipulating, and reporting on data.Database StructureIn the early days of computing, a database generally consistedof a single file that was divided into data blocks thatin turn consisted of records and fields within records. TheCOBOL language was (and is) particularly suited to reading,processing, and writing data in such files. This flatfile database model is still used for many simple applicationsincluding “home data managers.” However, for morecomplex applications where there are many files containinginterrelated data, the flat file model proves inadequate.Because both the Customer Record and the Transaction Recordinclude the Customer Number field, it is easy to pull informationfrom both databases into a single report, such as a summary of purchasesfor each customer.In 1970, computer scientist E. F. Codd proposed a relationalmodel for data organization. In the relational model,data is not viewed as files containing records, but as a setof tables, where the columns represent fields and the rowsindividual entities (such as customers or transactions).A field (column) that two tables have in common (calledthe key) can be used to link the two. For example, considera table of customer information (name, customer number,address, current balance, and so on) and a table of transactioninformation (product number, quantity, customernumber of purchaser, and so on).To find all the items purchased by a particular customer,the relational database uses the common field (the customeraccount number) to join the two tables. A query can thenselect all records in the transaction file whose customernumber field matches the current customer in the customerfile. (Notice that the validity of a key field depends on itsbeing unique: If each customer doesn’t have one [and onlyone] customer number, any report of purchases will not bedependable.)A procedure called normalization is often used to createa set of tables from a set of data files and records, such thatno fields contain duplicate information. This is necessary inorder to ensure that a piece of information can be updatedand the update “propagated” to the entire database withoutmissing any instances.Relational databases usually also enforce referential integrity.This means preventing changes to the database fromcausing inconsistencies. For example, if table A and table Bare linked and a record is deleted from table A, any links tothat record from records in table B must be removed. Similarly,if a change is made in a linked field in a table, recordsin a linked table must be updated to reflect the change.During the 1980s, the dBase relational database programbecame the most popular DBMS on personal computers.Microsoft Access is now popular on Windows systems,