Coded Record Structures

[Chris Sharman]

>Also, I was wondering about the efficiency of this technique.  When
>retrieving data, is it a sequential read using the code value?  Since the
>coded item is common to each variant record in the file, couldn't
>(shouldn't) it be defined as an index for faster reads?   Can this element
>be defined both as a "select value" AND as an index?

The sequential read technique is efficient for code values that appear in most
record buckets, and obviously inefficient for rare code values.
Conversely, indexed read is efficient for rare code values, but RMS will choke
somewhat if you run to thousands of duplicate keys. One way to alleviate that
is to use the RMS null value facility to eliminate the commonest key.

Eg: header record, data records (lots), trailer record: make the data record
value the null key, read them sequentially, the rest by key.

>Are select values REQUIRED for coded record structures or will Powerhouse
>(or RMS) allow the user to create a file with more than one variant record
>structure and NO coded values?  Such that the programmer could control
>update and retrieval directly via the code.

You could construct your own in the dictionary using redefines and
substructures ( _ and . ).

It's a historical curiosity: I've struggled with it occasionally when required
to handle data someone else has organised in this way. It saves a few bytes at
the expense of extra complexity - that used to be worthwhile, but not for some
years now.

Chris
_______________________________________________________________________
Chris.Sharman@CCAgroup.co.uk		http://www.ccagroup.co.uk/
CCA Stationery Ltd, Eastway, Fulwood, Preston, Lancashire, PR2 9WS.


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