Database Reference
In-Depth Information
These diagrams were the starting points for database management systems that used
either networks or hierarchies as the basic structure for their data. Both the network
databases and the hierarchical database systems were built on the premise that data
elements would be linked together by pointers.
Next
Next
Parent
Prior
Prior
Direct
Direct
1st child
n
th child
Next
Prior
Prior
Next
Direct
2nd child
Next
A closed chain of records in a navigational database model (e.g. CODASYL), with
, and
next pointers, prior pointers
direct pointers
provided by keys in the various records.
Next
Parent
Prior
Empty set
Illustration of an
empty set
Customer 1
Customer 2
Customer
Customer-order
set 2
Customer-order
set type
Order 1
Order 3
Order 4
Customer-order
set 1
Order 5
Order
Order 2
Expanded diagram
(longhand representation)
Bachman diagram
(shorthand representation)
Illustration of a set type using a
Bachman diagram
The record set, basic structure of navigational (e.g. CODASYL) database model. A set consists
of one parent record (also called “the owner”), and n child records (also called members records)
An example of a navigational database model with pointers linking records
