The IBM IMS Database element stores information
using a hierarchical model, which is quite different from IBM's later launched
relational database, DB2. (DB2 gets its name because IMS, which was designed
first, was DB1.) In IMS, the hierarchical model is applied using prevents of
information known as segments. Each segment can contain several parts of
information, which are known as fields. For example, a client database may have
a main segment (or the segment at the top of the hierarchy) with fields such as
phone, name and age. Kid segment may be included beneath another segment, for
example, one purchase section under each client section comprising each
purchase a client has placed with an organization. Furthermore, each purchase segment
may have many kids segment s for each product on the deal. As opposed to other
directories, you do not need to determine all of the information in a segment
to IMS. A section may be described with a dimension 40 bytes but only determine
one area that is six bytes lengthy as a key field that you can use to discover
the segment when doing inquiries. IMS will recover and preserve all 40 bytes as
instructed by a system but may not comprehend (or care) what the other bytes
signify. In exercise, often all information in a segment may map to a COBOL
copybook. Besides DL/I question utilization, a field may be described in IMS so
that the information can be invisible from certain programs for protection
factors. The database part of IMS can be bought separate, without the deal
administrator element and used by techniques such as CICS.
There are three primary types of IMS hierarchical
databases:
Full Function Databases
·
Directly descended from the Data Language
Interface (DL/I) databases initially developed for Apollo. Full function
databases can have basic and secondary indexes, contacted using DL/I call from
your application program, like SQL calls to DB2 or Oracle.
·
Full function databases can have a range of
access methods, although Hierarchical Direct (HDAM) and Hierarchical Indexed
Direct (HIDAM) rule.
·
The other layouts are Simple Hierarchical
Indexed Sequential (SHISAM), Hierarchical Sequential (HSAM), and Hierarchical
Indexed Sequential (HISAM).
·
Full function databases store data using VSAM, a
native z/OS access technique, or Overflow Sequential (OSAM), an IMS-specific
access technique that optimizes the I/O channel program for IMS access
patterns. In particular, OSAM performance benefits from chronological access of
IMS databases (OSAM Sequential Buffering).
Fast Path Databases
Fast Path databases are optimized for tremendously high
transaction rates. Data Entry Databases (DEDBs) and Main Storage Databases
(MSDBs) are the two kinds of fast path databases. Neither provides any
indexing. Virtual Storage Option (VSO) DEDBs can replace MSDBs in contemporary
IMS releases, so MSDBs are slowly disappearing.
High Availability Large Databases (HALDBs)
IMS V7 initiated HALDBs, an addition of IMS full function
databases to offer better availability, better handling of tremendously large
data volumes, and, with IMS V9, online reorganization to support uninterrupted accessibility.
(Third party tools exclusively offered online reorganization prior to IMS V9.)
A HALDB can store in surplus of 40 terabytes of data.
Related Exams
Followings are the some exam codes related to IBM
IMS issued by IBM:
·
000-036
·
000-443
·
000-546
·
000-730
·
000-M66
·
000-M68
·
000-M70
·
000-M71
·
000-M72
·
000-M73
·
000-M75
·
000-M77
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