IMS Hierarchical Database
Oracle Tips by Burleson Consulting
High Performance Data Warehousing
Early Commercial Databases
The problems associated with flat-file
systems led to the development of the first commercial database--IMS
(Information Management System), from IBM. IMS is considered a
hierarchical database, meaning that pointers are used to establish
the data relationships. IMS remains very popular today, and it is
well suited for modeling systems in which the entities are naturally
hierarchical in nature. The data relationships are established with
child and twin pointers, and these pointers are embedded into the
prefix of every record in the database (see Figure 1.5).
Figure 1.5 Hierarchical databases.
Many data warehouses are populated from data extracted from IMS
databases, so a discussion of the internals of IMS will help the
warehouse administrator develop a plan for extraction from IMS.
While IMS is very good at modeling naturally hierarchical data
relationships, complex data relationships, such as many-to-many and
bill-of-materials relationships, have to be implemented in a very
clumsy fashion, with the use of phantom records. The IMS database
also suffers from its own complexity. Learning to program and
administer an IMS database requires many months of training, and,
consequently, IMS development remains very slow and cumbersome.
It is interesting to note that while IMS is considered a dinosaur by
today's computer standards, IBM continues to sell new copies of IMS,
and IMS is still used by hundreds of corporations that require
high-speed Online Teleprocessing (OLTP) applications. While some of
these systems are legacy systems, which are not easily converted to
modern technology, many corporations continue to use IMS because of
its high speed. A hybrid of IMS, called IMS/FASTPATH, is one of the
fastest commercial databases available, even by today's standards.
IMS/FASTPATH is used at companies that may have hundreds, or even
thousands, of concurrent transactions, and some IMS configurations
have surpassed the 1000 transactions per second barrier.
As fast as IMS is for highly normalized OLTP systems, the
de-normalized nature of data warehousing makes much of the fast
access of IMS unusable for data warehouses. Consequently, the
hierarchical database model remains firmly entrenched in OLTP
This is an excerpt from "High Performance
Data Warehousing", copyright 1997.
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