> -----Original Message-----
> From: IBM Mainframe Discussion List On Behalf Of John McKown
> Sent: Thursday, December 18, 2014 9:03 AM
>
> On Thu, Dec 18, 2014 at 8:36 AM, Chase, John <[email protected]> wrote:
>
> > > -----Original Message-----
> > > From: IBM Mainframe Discussion List On Behalf Of Jon Butler
> > > Sent: Thursday, December 18, 2014 8:19 AM
> > >
> > > I'd like to state that even after 30 years of MVS, I still use the
> > > term
> > "file" when referring to
> > > mainframe datasets. In fact, if you look at the IBM COBOL manual,
> > > you
> > will see "File Organization",
> > > not "Dataset Organization"; PL/I refers to "FILE Attributes", etc.
> > > And
> > I think I can safely say I
> > > have never seen a DD NULLDATASET command ;-))
> > >
> > > Don't be too hard on people just trying to learn.
> >
> > Q: What's the "structural difference" between a DB2 Table and a VSAM KSDS?
> >
> > A: The DB2 Table contains "rows" and "columns". The VSAM KSDS
> > contains "records" and "fields".
> >
>
> Hum, I might go a bit further. A VSAM KSDS is a disk data set which contains
> "records". A KSDS does
> not contain "fields" known to the access method. Therefore a VSAM KSDS does
> not have any "fields" in
> it. The "fields" within a KSDS record are imposed by the program reading the
> data set by overlaying
> the buffer contain the record with a template (COBOL FD or equivalent). VSAM
> itself does not know
> anything about them. At most, VSAM knows the location and length of the key
> data. This key data could
> be a single field or a composite of multiple fields in some application.
>
> BTW, have you been reading some of Joe Celko's SQL books? That, in general,
> is one thing he is
> constantly emphasizing about the difference between "files" (he doesn't use
> "data set") and
> "databases". As he keeps drumming:
> A table IS NOT a file! A "row" is not a "record". And a "column" is not a
> "field".
Yabbut....
The "structure" of a DB2 table is "imposed" by the table definition, just like
the "structure" of a KSDS is "imposed" by the DSECT (or HLL equivalent). The
"access method" in both cases is still VSAM (ignoring the difference between
"CI access" for the LDS used by DB2 and the "logical record access" "normally"
used for a KSDS); SQL is the "API" for DB2, while "RYO" applies for KSDS.
At the lowest level, on DASD both are just "strings of ones and zeroes". :-)
-jc-
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