Quantcast Figure  3-7.Example  of  a  list  database  structure

 
  
 
database is it permits the maintenance of a related set of files or tables that can provide information to several different  users.  So  how  do  these  database  structures differ? you might ask. That’s a good question. Read on and find out. LIST  DATABASES.—  List  databases  link  records together through the use of pointers. The pointer is a data  element  in  one  record  (normally  the  master  record) that   points   to   the   actual   disk   location   of   another logically related record, as illustrated in figure 3-7. HIERARCHICAL DATABASES.— Hierarchical databases  consist  of  elements  that  act  in  a  superior- subordinate   or   parent-child   relationship.   What   this means is that one element is linked to another element in the  database.  The  superior  element  points  to  one  or more  subordinate  elements.   There   can   also   be   a subordinate of a subordinate, which will enable many hundreds of elements to be connected. See figure 3-8. NETWORK  DATABASES.—  Network   databases are  very  similar  to  hierarchical  databases  except  that  an element  can  have  one  or more  superiors.   Network structure   permits   the   connection   of   the   nodes multidirectionally.  Each  node  may  have  several  owners (or elements) and may own any number of other data elements on the network (see figure 3-9). The database management software permits the extraction of needed information  from  such  a  structure  to  begin  with  any record in the file. Although network databases are more Figure  3-7.—Example  of  a  list  database  structure. Figure  3-8.—Example  of  a  hierarchical  database  structure. flexible  than  hierarchical  databases,  they  still  have limitations.  The  networking  scheme  must  be  defined when the database is initially created, and information retrieval is based solely on the predefined scheme. Figure  3-9.—Example  of  a  network  database  structure. 3-13

 


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