Quantcast Database Management Systems (DBMS)

l Sequential file organization.  In  sequential  file organization, the records are in the same order as they were written to the file. l  Indexed  sequential  file  organization.   In indexed  sequential  file  organization,  the  records  are stored in sequence according to a primary key and an index is created to allow random access of the file. This type of organization also allows the file to be accessed sequentially. Indexed sequential is the most commonly used type of file organization. l   Direct   file   organization. In   direct   file organization, the records are stored and retrieved using a relative record number, which gives the position of the record in the file. This type of organization also allows the file to be accessed sequentially. DATABASE  MANAGEMENT  SYSTEMS (DBMS) A   database   management   system   (DBMS)   is   a software package that provides an integrated source of data for multiple users, while presenting different views of that data to different users. It can be characterized as generalized  software  that  provides  a  single  flexible facility   for   accommodating   different   data   files   and operations, while demanding less programming effort than conventional programming languages. It features easy  access  to  the  data;  it  facilitates  the  storage  and maintenance   of   large   volumes   of   data;   and,   most importantly, it provides the capability for sharing the data resources among different types of users. Database   management   systems   range   from elementary   systems   with   single   record   structures, providing  rudimentary  report  formatting  facilities,  to very  elaborate  systems. The  very  elaborate  systems handle   several   files   with   hierarchical   or   relational structures,  perform  functions  in  an  online  mode,  and have   sophisticated   query   and   report   writing capabilities. DBMSs  are  being  used  on  a  wide  variety  of computers in the Navy. Because of this, no one DBMS by  any  single  manufacturers  discussed  in  this  chapter. Most  of  the  problems  with  DBMSs  in  Navy computer   systems   are   the   same   as   in   the   civilian workplace. A  few  of  these  problem  areas  are  noted below: . Users do not want to share their data with others in the database. . Data representation is inadequate. .   Privacy   and   safeguarding   of   proprietary information are not sufficient. . Different views of data are needed by technical and nontechnical DBMS users. . Data structures are not tailored to individual user requirements. The wide use of DBMSs in the Navy indicates that all  or  most  future  operating  systems  will  be  oriented primarily toward DBMS. Slowly, but surely, the DBMS problems  in  the  preceding  list  are  being  eliminated through   better   and   more   sophisticated   software, coupled   with   advanced   training   of   users   on   such software usage. Take  a  look  at  the  changes  that  have  been  made from   the   conventional   system   file   structure   to   the database  management  system  structure.  As  shown  in figure 3-13, a conventional system is many application Figure  3-13.—A  conventional  system. 3-21


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