SAS(R) 9.1.3 Companion for z/OS

54 Assigning SAS Data Libraries Internally Chapter 2
users from allocating the library until you de-allocate the library. In order to
update any member of a library, you must request exclusive access to the
library data set.
3 Specifying a disposition status of SHR will request shared access to the
library. The allocation will succeed provided that no other job or users have
the library allocated for exclusive access, and z/OS will prevent other jobs or
users from allocating the library for exclusive access until you de-allocate the
library. However, other SHR allocations can exist concurrent with yours.
You can allocate the z/OS data set external to SAS using z/OS facilities such as JCL
or the TSO ALLOCATE command. In most cases, SAS will use the external allocation
to process the library. This is always true if the DDname of the allocation is specified as
the libref. However, if SAS does not find an external allocation of the library data set, it
will dynamically allocate the library data set when assigning a library internally. When
this is necessary, SAS will allocate a library with a disposition status of OLD, unless a
different status has been specified. The DDname used for this allocation will be the
same as the libref unless the libref is not a valid DDname or is a DDname that matches
the libref that is already allocated. In those cases, SAS must let the operating system
generate a unique DDname, which would be in the format SYSnnnnn.
Once SAS has allocated a library data set, it will use that allocation to process the
library, regardless of how many librefs are assigned to the library and provided that the
same disposition status is specified (or implied) on all the assignments. See “Assigning
Multiple Librefs to a Single SAS Data Library” on page 60 for more information.
However, if a library is assigned with a disposition status of SHR and later, an
additional assignment is made with a status of OLD, SAS will attempt to dynamically
allocate the library data set a second time using a disposition status of OLD and a
system-generated DDname. If successful, this second allocation will be used for all
subsequent processing of the library until all librefs associated with the library have
been de-assigned. Note that in this case SAS will not (and cannot) release exclusive
access to the library even when you release the assignment that specified a status of
OLD.
Assigning SAS Data Libraries Internally
SAS provides two methods for assigning SAS data libraries internally, that is, via
SAS statements without relying on operating environment facilities such as JCL:
3 The LIBNAME statement or LIBNAME function can be used to assign a SAS data
library.
In the following example, the data library USER934.MYLIB.SASLIB has been
assigned to the libref MYLIB. The z/OS allocation parameter DISP=SHR requests
shared access to the library data set. Since no engine was specified, SAS will
examine the format of the library data set to determine which engine to use.
libname mylib ’user934.mylib.saslib’ disp=shr;
In the data step below, the libref MYLIB is used to refer to the library. MYLIB
can be used for the remainder of the SAS session until explicitly cleared by a
LIBNAME CLEAR statement.
data mylib.member1;
...
run;
Except for a few special cases, the LIBNAME statement or function can perform
all of the assignment functions that are required for SAS data libraries. The