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Physical & logical data base in DL/I data base

 
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KAMALAK

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Joined: 18 Jul 2005
Posts: 12

PostPosted: Thu Sep 29, 2005 10:40 am    Post subject: Physical & logical data base in DL/I data base
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hi i am new to IMS DB/DC i am studying this form IMS FOR THE COBOL PROGRAMMING by steve eckolos.......but i would like to know the structure of IMS data base just like DB2 as tables........
and also actually what is physical and logical database
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priyesh.agrawal

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Joined: 28 Mar 2005
Posts: 1452
Location: Chicago, IL

PostPosted: Thu Sep 29, 2005 11:05 am    Post subject: Re: Physical & logical data base in DL/I data base
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Hi Kamalak,
Quote:
i would like to know the structure of IMS data base just like DB2 as tables........

IMS is a Hierarchical Database, while DB2 is a Relational Database.

In IMS, data is stored in hierarchical manner.
There is a parent segment which can have multiple child segments. They are known as Siblings in IMS Terms.
There can be more than one occurrences of a child for Parent, such occurrences are known as Twins in IMS.

Quote:
and also actually what is physical and logical database

You are going thru Steve Eckols....You'll come across a term in IMS called PSB. PSB defines some part of the database to be accessed. You create & use PSB's as per your Database need. This PSB can be referred as Logical Database for IMS.

Regards,

Priyesh.
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KAMALAK

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Joined: 18 Jul 2005
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PostPosted: Thu Sep 29, 2005 2:21 pm    Post subject: Re: Physical & logical data base in DL/I data base
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thanks priyesh for u r reply
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varunraisharma

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Joined: 01 Sep 2005
Posts: 15
Location: Bangalore

PostPosted: Thu Sep 29, 2005 5:35 pm    Post subject: Re: Physical & logical data base in DL/I data base
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Physical database : it is defined by the DBD (Database Descriptor). It denotes the physical structure(actual structure) of the database.

Logical databse : it is defined by the PSB (Program Specification block). It denotes the application's view of data.

There is only one DBD but there can be many PSBs one for each different applications as there can be many different views of a database.

Regards
Varun
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