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If
the
nam4ed
data
set
is
stored
on more than 20 vol urnes, bytes
253-255 of the block contain the relative
track
address
of
the
next
block of volume pointers.
Byte 256 contains a binary zero.
Example:
In
the
following
example, the list of volumes that contain
data set A.B is read into main storage.
The search for the
volume-list
block starts on the system residence volume.
r---------T----------T-------------------------------------------------,
I Name
I Operation I Operand
~
~---------+----------+-------------------------------------------------i
I
I LOCATE
I INDAB
READ VOLUME-LIST BLOCK FOR
I
I
I Check Exceptional Returns
CATALOGED DATA SET A.B INTOI
I INDAB
I
CAMLST
I
NAME,AB"LOCAREA
MAIN STORAGE AREA NAMED
I
I
AB
I DC
I
CL44'A.B'
LOCAREA.
LOCAREA ALSO
I
I
LOCAREA
I
DS
I OD
CONTAINS 3-BYTE TTR AND
I
I
I DS
I
265C
6-BYTE SERIAL NUMBER
I
L _________
~
___________
~
_________________________________________________ J
The
LOCATE macro-instruction points to the CAMLST macro-instruction.
NAME, the first operand of CAMLST,
specifies
that
the
system
is
to
search
the
catalog for a volume-list tlock by using the name of a data
set.
AB, the second operand, specifies the main storage location
of
a
44-byte
area
into
which you have placed the fully qualified name of a
data set.
LOCAREA, the fourth operand, specifies a
265-byte
area
you
have reserved in main storage.
After
execution
of
these
macro-instructions,
the
265-byte
area
contains: the 256-byte volurre-list block for data set
A.B,
the
3-byte
relative
track
address
(TTR) of the block following the one read into
main storage, and the 6-byte serial number of the volume
on
which
the
block was found ..
Specifying the Name of a Generation Data Set
You
specify
the
name
of
a generation data set by using the fully
qualified generation index name and the relative
generation
number
of
the
data
set.
The value of a relative generation number reflects the
position of a data set in a generation data group.
The following values
can be used:
• Zero - specifies the latest data set cataloged in a generation
data
group.
• Negative
nt~ber
- specifies
a data set cataloged before the latest
data set.
• Positive number - specifies a data set
not
yet
cataloged
in
the
generation data group.
When
you
use
zero
or a negative number as the relative generation
number, a volume-list block is read into main storage and
the
relative
generation number is replaced by the absolute generation name.
When
you
USE~
a positive number as the relative generation number, an
absolute generation name is created and replaces the relative generation
number.
A volume-list block is not read, since none
exists
for
these
data sets.
Example:
In
t.he
following
example, the list of volumes that contain
generation data set A.PAY(-3) is read into main storage.
The search for
the volume-list block starts on the system residence volume.
Maintaining the Catalog and the Volume Table of contents
11
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