IMS (database)

See also: IMS

IMS (for Information Management System ) began like a hierarchical Database created by IBM in 1966 for the account from Rockwell and the Programme Apollo. It was used to follow the invoices of the materials for the program Saturn V.

IMS is always in the course of operation 40 years after its launching and continuous to give place to developments under the operating system MVS of IBM (OS/390, Z/OS).

There are three basic principles for a hierarchical database:

  1. Full Function

  2. * “Full Function” is a language which resembles much “Data Language/1 (DL/I)” developed for the Apollo program. The databases “Full Function” can have primary education and secondary indices and are accessible via Requête S DL/I.
  3. * These databases have a large variety of access methods, although “Hierachical Direct (HDAM)” and “Hierarchical Indexed Direct (HIDAM)” are privileged.
  4. * the other possibilities are “Simple Hierarchical Indexed Sequential (SHISAM)”, “Hierarchical Sequential (HSAM)” and “Hierarchical Indexed Sequential (HISAM)”.
  5. * In this basic type of data, the data are stored by using method “VSAM” (a native access method of system MVS) or the method “OSAM” (Overflow Sequential, a specific method which optimizes the accesses for IMS). Method “OSAM” has the advantage of having a management especially conceived for it in the bases IMS (OSAM Sequential Buffering) which increases its performance.
  6. database IMS also has rapid accesses - 'Data Entry Databases (DEDB) and 'Hand Storage Databases (MSDB). These two kinds of databases do not allow any indexing, but are conceived for very high bancs of information. On the recent versions of IMS, method “MSDB” can be replaced by virtual storage (VSO - Virtual Storage Option).
  7. With version 7.1 of IMS, a new extension “high availability” was introduced (HALDB - Broad High Availability Database). It allows a better availability of the data, a better management of very large volumes of data (and even an in line reorganization with version 9).

IMS is also a manager of transactions. The manager interacts with an end user (connected via VTAM or TCP/IP and, in the same way as an interface Web using of scripts cgi, provides an interface allowing to carry out requests or to update databases IMS or DB2).

IMS uses the principle of the files of requests. An entering transaction (since a terminal) is received by controller IMS, then stored in the file of messages ( message tail ). When a transaction was put in the file, IMS calls upon its ordonnancor to start the program of the user in a reserved zone ( area ). The message is then treated and withdrawn of the queue, the data are stored or updated and an answer is possibly inserted in the queue of IMS to be dispatched with the user.

If you already withdrew from the money of a Automatic teller machine (ATM in English), there is a strong chance so that your request was treated by a system of the type IMS.

See too

  • CICS

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