Coded Record Structures

[pablo grim]

VMS 7.1
Powerhouse 7.4f4

I'm curious about the purpose of these coded record structures.
Specifically the "select item" in the record structure.  Why is this
functionality in the dictionary rather than in the code?  Isn't this a
function that the programmer could control in code.  It's kind of hidden
away there in the dictionary.

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?

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.

I guess I'm quite lost as to the nature and purpose of the select value item
in this interesting data structure.

thanks

Paul Grim
Progressive Computing