Database Concepts › Data Structure Diagrams › Representing Sets Graphically

Representing Sets Graphically

The following information about each set type is included in the data structure diagram:

• Set Name- Name of the set type
• Set Linkage- For chain sets, the set linkage options as:
  • N (next pointers)
  • NP (next and prior pointers)
  • NO (next and owner pointers)
  • NPO (next, prior, and owner pointers)

  For index sets, the set linkage options as:

  • I (index pointers)
  • IO (index and owner pointers)
  • U or blank (unlinked - no pointers)
• Membership Options- The disconnect/connect options:
  • MA (mandatory automatic)
  • MM (mandatory manual)
  • OA (optional automatic)
  • OM (optional manual)
• Order- The position in which new records are added to the set
  • FIRST
  • LAST
  • NEXT
  • PRIOR
  • SORTED identifying the ordering sequence (ASC for ascending, DES for Descending), sort or symbolic key element(s) and duplicates options (DN, DF, DL)

For more information about the meaning of the above options, see Sets.

The following figure illustrates the graphical representation of the DEPT-EMPLOYEE chain set. This set is linked through NEXT, PRIOR, and OWNER pointers. It is a Mandatory Automatic set and new members are inserted at the end of all existing members.

The next figure illustrates the graphical representation of the system-owned index SKILL-NAME-NDX and the user-owned index set SKILL-EXPERTISE. Both sets are linked through an INDEX pointer and sorted on an index key: SKILL-NAME-0456 and SKILL-LEVEL-0425 respectively. However, owner pointers are maintained for the user-owned index set SKILL-EXPERTISE and skill names are unique whereas skill levels are not because several employees might have the same level in a given skill. Furthermore, members of the SKILL-EXPERTISE set are maintained in descending skill level sequence and a new record whose skill level matches that of an existing member is inserted logically before the existing member.

The following is the complete data structure diagram for Commonweather Corporation.