【正文】 related data elements that may be structured in various ways to meet the multiple processing and retrieval needs of anizations and individuals． There’ s nothing new about databases—early ones[1] were chiseled in stone，penned on scrolls， and written on index cards． But now databases are monly recorded on magizable media， and puter programs are required to perform the necessary storage and retrieval operations． You’ll see in the following pages that plex data relationships and linkages may be found in all but the simplest databases[2]． The system software package that handles the difficult tasks associated with creating， accessing， and maintaining database records is called a database management system（ DBMS）． The programs in a DBMS package establish an interface between the database itself and the users of the database．（ These users may be applications programmers，managers and others with information needs， and various OS programs．） A DBMS can anize， process， and present selected data elements from the database． This capability enables decision makers to search， probe， and query database contents in order to extract answers to nonrecurring and unplanned questions that aren’t available in regular reports[3]． These questions might initially be vague and / or poorly defined， but people can“browse”through the database until they have the needed information． In short， the DBMS will“manage”the stored data items and assemble the needed items from the mon database in response to the queries of those who aren’t programmers． In a fileoriented system， users needing special information may municate their needs to a programmer， who， when time permits，will write one or more programs to extract the data and prepare the information[4]． The availability of a DBMS， however， offers users a much faster alternative munications path（ see Fig. 71）． If the DBMS provides a way to interactively and update the database, as well as interrogate it capability allows for managing personal dataAces however, it does not automatically leave an audit trail of actions and does not provide the kinds of controla necessary in a multiuser anization. Thesecontrols are only available when a set of application programs are customized for each data entry and updating function. Software for personal puters which perform me of the DBMS functions have been very popular arsenal puters were intended for use by individuals for personal information storage and process These machines have also been used extensively small enterprises, professionals like doctors, acrylics, engineers, lawyers and so on ． By the nature of. intended usage, database systems on these machines except from several of the requirements of full doge database systems． Since data sharing is not： Tended, concurrent operations even less so, the) fewer can be less plex. Security and integrity7aintenance are deemphasized or absent. As data) limes will be small, performance efficiency Is also important. In fact, the only aspect of a database system that is Important 39。is data Independence. , as stated earlier. Means that applicant programs and user queries need not recognizant‘physical anization of data on secondary storage. The importance of this aspect, particularly for the personal puter user, is that this greatly simplifies database usage. The user can store, access and manipulate data at a high level (close to the application) and be totally shielded from the low level (close to the machine) details of data anization. We will not discuss details of specific PC DBMS software packages here． Let us summarize in the following the strengths and weaknesses of personal puter database software systems： The most obvious positive factor is the user friendliness of the software. A user with no prior puter background would be able to use the system to store personal and professional data, retrieve and perform relayed processing. The user should, of course, satiety himself about the quality of software and the freedom from errors (bugs) so that investmerits in data arc protected. For the programmer implementing applications with them, the advantage lies in the support for app