introduction to dBASE Ⅲ  

　　Although database management is a computer:crm, it can also apply to the ways in which informa-.ion s catalogued, stored, and used. At the center ofany information management system is a database  collection of related information grouped toether as a single itcm is a database. Metal filing,abincts with customer records, a card file of namesand phone numbers，and a notebook with a penciledisting of a store inventory arc all databases How--N,er, a cabinet or a notebook does not make a data  the way information is organized makes it aJatabase. Objects like cabinets and notebooks onlyaid in organizing information, and dBASE III is onesuch aid.   
　　Information in a database is usually organizedand stored in a table with rows and columns‘For-xampic, a mailing list in database form, each rowcontains a name, an address, a phone number, and：ustomer number. Each row is related to the othersDecause they all contain the same types of forniaion. And because the mailing list is a collection ofaformation arranged in a specific order一a column}f names, a column of addresses, a column of cus-.omer numbers一it is a database.     
　　Rows in a database file are called records andcolumns are called fields．As an illustration, comparea database file to an address filing system kept in abox of 3 X 5 file cards．Each card in the box is asingle record, and each category of information on acard is a field. Fields can contain any type of infor-mation that can be categorized. In the card box, eachrecord contains six fields：a name, address, city, state,ZIP code, and phone number. Since every card in thebox has the same type of information, the card box isa database box.   
　　In theory, any database is arranged in such away that information is easy to find. In the mailinglist database, for example, names are arranged alpha-betically. If you want to find the phone number of acustomer, simply locate the name and read across tothe corresponding phone number.   
　　You are already interested in how a computer-ized database management system can make informa-tion storage and retrieval more efficient than a tradi-tional filing system, and you will find that dBASE IIIoffers many advantages．A telephone book, for in-stance, is fine for finding telephone numbers，but ifall you have is an address and not the name of theperson who lives there, the phone directory becomesfairly useless for finding that person's phone numberA similar problem troubles office filing systems．if the information is organized by name and you want tofind all the clients located in a particular area, you　could be in for a tedious search．In addition, organiz-ing massive amounts of information into written di-rectories and filing cabinets can consume a great dealof space. A manual database can also be difficult tomodify. For example, adding a new phone numbers tothe listing may mean rearranging the list. If the phonecompany were to assign a new area code, someonewould have to search for all phone numbers havingthe old area code and then replace it with the newone.   
　　When a database is tcamed with a computermany of these problems arc eliminated, A computer-ized database provides speed finding a phone numberfrom among a thousand entries takes less than twoseconds, and sorting a database with a hundred itemsrequires less than two minutes．A computerized database is compact: a database with over 10000 itemscan be storcd on a small disk. A computerized data-base is flexible: it has the ability to examine informa-tion from a number of angles, so you, for example,could automatically search for a phone number byname or address．   
　　A word processing program can be used to or-ganizc data in the form of a list; however, it wills offeronly limited flexibility. You still have to sort, rearrange, and access the information.   
　　A step above word processing is the simple filemanagers．File managers are relatively inexpensiveprograms that use database files to store informationMost file managers can also do sorting and otherclerical tasks．   
　　Database managers also store information indatabase files, but in addition to being more sophisti-cated than file managers, they can access informationfrom more than two database files simultaneously, whereas a file manager can access only one databasefile at a time. Being able to work on only one database file can be severely limiting. If the file manageris accessing information from one file, but needsthree fields of information from a second file, the filemanager can't continue unless the second databasefile is available. Only after the file mapager is finished with the first database file can it proceed to thesecond databasc file.But what good is this when the file manager needs information from both databasefiles simultaneously? The only solution is to duplicatethe three fields from the second database file into thefirst database file. Fortunately, this is not a problemwith a database manager like dBASE III．