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Chapter 22. Librarian
Both VSE and OS/390 have facilities to help you define, organize, and manage
libraries of system data. In VSE these system facilities are called the
Librarian
.
In OS/390, the equivalent function is provided by Partitioned Data Sets (PDS) and
the newer Partitioned Data Set-Extended (PDSE), and the group of utilities used
for their management, including the Partitioned Access Method (PAM) and the
Interactive System Productivity Facility (ISPF).
The following briefly describes VSE and OS/390 library support.
22.1 Overall Library Support
One of the most important utilities in VSE is the VSE Librarian which allows you
to back up, restore and re-organize VSE libraries. In OS/390, there are a group of
utilities which provide similar functions and capabilities.
Generally, a librarian is a program or a group of programs which serve to
organize and maintain the libraries of a system including both system and user
program source, object, and load modules. It also contains service functions to
display and punch parts of them or display their directories and to set up and
change the library concatenation chains and their control tables.
The concept of a librarian is based on the following aspects:
•
Logical library structure
A VSE library is logically divided into sublibraries. Each sublibrary may
contain members of any type (procedures, source books, object modules,
phases, user-defined types). This makes a library common for all types of
members. Therefore, a component consisting of procedures, source books,
object modules, and phases may be put into one library and even into one
sublibrary.
In OS/390, a partitioned data set contains a directory and a collection of
members. A single PDS (or PDSE) logically corresponds to a sublibrary in
the VSE paradigm. It is usual, however, to place members of different types
(source, object or load members) into different PDSs in OS/390
environments.
•
Library data format
VSE library data is blocked, resulting in good utilization of DASD space. The
VSE library data format allows space to be reused. Space freed due to
deletion of a member is available for reuse without requiring a condense
run. The member directories are sorted, improving retrieval times.
Partitioned Data Sets in OS/390 need to be compressed periodically. Use of
PDSE structures reduces (or eliminates) this need. Also, PDSE data sets
maintain the order of entries in their directories to improve performance
compared to PDS structures.
•
Librarian command language
The VSE Librarian consists of a single program, and its commands follow a
consistent pattern. They are powerful and easy to use. They reflect the
Copyright IBM Corp. 1998 389