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[tramasamy]

Hi,

Could u please let me know the diffrence between the follwoing DBs

1) IMS Full Function Database
2) IMS Fast path Database
3) IMS Main Storage DataBase.

Alos let me know the advanatages fo each DB

Thanks
Rams

[kolusu]

tramasamy,

IMS Database Often referred to as "DL/1 database" or colloquially as "Full-function database". DL/1 databases provide an hierachically structured database, that can be accessed by record or sequentially, and by other sequences that were planned and provided for when the database was designed. DL/1 databases are limited in size to 4GB or 8GB per data set unless the Partioned Database product is used.

Full Function IMS DB (DL/1 DB) :IMS Full Function Database was design to support most types of databases. It can be used in a wide variety of applications. Most IMS applications make us of full function database unless there are specific requirements to one of the other types of databases.

The major characteristics of full function database are

• Small or Large databases
  
• Access to records via a unique or non-unique keys
  
• Many types of segments (up to 15 level allowed)
  
• Records can be stored in Key sequence but it is not a requirement.
  

DEDBs The Data Entry database, often referred to colloquially as "Fast Path databases". These are particularly suited for use where large databases, or very low processing costs are required, or particularly high data availability, or very high performance is required

FastPath Data Entry Database (DEDB) : The Data Entry database was designed to support particularly access intensive IMS database requirements, primarily in the banking industry, for:

• Large databases containing millions of records, extending well beyond the original 4GB database limits of DL/1 databases
  
• Access to each database record can be achieved by access via a key field;
  
• Lower processing costs per database record and per update than are required for DL/1
  databases
  
• The capability to support higher transaction workloads than DL/1 can sustain, while maintaining the per-transaction cost advantages mentioned above
  
• Improved availability, with reduced requirements for database outage, especially for database maintenance activities such as database reorganizations
  
• Lower processing costs for particular types of processing, where data are inserted on-line and retrieved in batches for further processing, and eventually deleted in batches
  
• The possibility of eliminating transaction-related I/O from database processing.
  

MSDBs(Main Storage Database) contain only root segments. Each segment is like a database record, because the segment contains all of the information about a particular subject. In a DL/I hierarchy, a database record is made up of a root segment and all its dependents. For example, in the medical hierarchy, a particular PATIENT segment and all the segments underneath that PATIENT segment comprise the database record for that patient. In an MSDB, the segment is the whole database record. The database record contains only the fields that the segment contains. MSDB segments are fixed length.

The two kinds of MSDBs are terminal related and non-terminal related. In terminal-related MSDBs, each segment is owned by one logical terminal. The segment that is owned can be updated only by that terminal. Related MSDBs can be fixed or dynamic. You can add segments to and delete segments from dynamic related MSDBs. You cannot add segments to or delete segments from fixed related MSDBs.

In the second kind of MSDB, called non-terminal related (or nonrelated) MSDBs, the segments are not owned by logical terminals.

I would also suggest that you read the following manual for a better understanding of IMS. This redbook is called a primer, as it is intended to be an introductory book to help familiarize the reader with the basics of IMS.

http://www.redbooks.ibm.com/redbooks/pdfs/sg245352.pdf


Hope this helps...

cheers

kolusu