TSS/360: Data sets

Instead of files, on TSS/360 we think about data sets, which are named collections of related records.

Data sets are collected into catalogs: the top level catalog contains one catalog for each user. Logged in as user TSS, you can see your catalog by typing PC? for print catalog:

pc?
DATA SETS IN CATALOG WITH QUALIFIER TSS*****
TSS*****.EREPOUT,   ACCESS: RO
TSS*****.SYSERP.G0004V00,   ACCESS: RW
TSS*****.GENMAC.G0005V00,   ACCESS: RW
...
TSS*****.SOURCE.HWORLD,   ACCESS: RW

A fully qualified data set name is a series of one or more names (called qualifiers) separated by dots. The first level is the user ID, so for our hello world program SOURCE.HWORLD under the user account TSS the fully qualified data set name would be TSS.SOURCE.HWORLD. You omit the user ID when dealing with your own data sets. Fully qualified data set names can be up to 35 characters long.

Partially qualified data set names represent a group of data sets, which acts somewhat like a directory on Unix. For example, the TSS user has two data set,s SOURCE.HWORLD and SOURCE.SYSGEN, doing PC? SOURCE will expand the partially qualified name and show both data sets.

pc? source
DATA SETS IN CATALOG WITH QUALIFIER TSS*****.SOURCE
TSS*****.SOURCE.SYSGEN,   ACCESS: RW
TSS*****.SOURCE.HWORLD,   ACCESS: RW

There's no concept of wildcards on TSS/360.

On operating systems like Unix, files are a collection of bytes and it's up to each program how to interpret them. But TSS/360 has several built-in types.

• Sequential - an unordered collection of records, for example a list of numbers that are an input to a program.
• Indexed - an ordered collection of records with a given key for each record. An example here, surprisingly, is a source code data set where each line is referenced by its line number.
• Region - like indexed, but also splits the data set into a number of different sections referenced by a region name.
• Partitioned - a group of several data sets from the above types contained in a single data set where each can be accessed separately. Similar to Unix libraries which are collections of object files with a header saying where to find them, but TSS/360 goes beyond this to collect all object code into a partitioned data set rather than it being a separate step.

You can find out what type a data set is with the DSS? command. Here we see SOURCE.HWORLD has the VI organisation, which means indexed.

dss? source.hworld

TSS*****.SOURCE.HWORLD
VOLUME: TSSRES (3330)
ORGANIZATION: VI             PAGES: 1
REFERENCED: 351/26           CHANGED: 350/26
RECORD FORMAT: V             RECORD LENGTH: 132
KEY LENGTH: 7                KEY POSITION: 4

The following codes are used:

Symbolic data definitions map a logical data set name to a physical data set. For example, programs read input from SYSIN and write to SYSOUT. In interactive use these will be the keyboard and terminal; in batch mode this will be the card input and the printer. It's possible to manipulate these from the command line using the DDEF and RELEASE commands; we'll see an example of doing this when programming with Fortran in a later post.

As well as being manipulated by programs, you can create and modify your own data sets. EDIT can be used for indexed or region data sets. Plain sequential data sets use a completely different editor called DATA. We'll look at both of these in more detail in a later post.

To rename a data set, use CATALOG with the U (update) and NEWNAME options. For example, to rename FOO to BAR:

catalog foo,u,newname=bar

The CDS command is used to copy data sets, for example to copy SOURCE.ABC to SOURCE.XYZ you would do:

cds source.abc,source.xyz

To remove a data set, use ERASE.

As mentioned above, partitioned data sets are collections of data sets; you can see the contents of a partitioned data set with POD?. Here we see our HWORLD object module in our user library USERLIB.

pod? userlib
SYSPRD
SYSPRO
HWORLD
SYSFCL

Each member of a partitioned data set can be accessed by giving the member's name in parentheses, so USERLIB(HWORLD) points to our object data set.

Partitioned data sets can be constructed using the copy data set CDS command. Say we have two source data sets SOURCE.MOD1 and SOURCE.MOD2 we want to add to a new partitioned data set MYSRC:

cds source.mod1,mysrc(mod1)
cds source.mod2,mysrc(mod2)

Removing members is done by ERASE:

pod? mysrc
MOD1
MOD2

erase mysrc(mod1)
pod? mysrc
MOD2

As we saw in the quick tour, data sets can be marked as generational to keep older versions around. You use CATALOG to define a data set and the number of versions - here I create a data set BAR with up to 5 versions.

catalog gno=5,gdg=bar

Rather than automatically saving a copy each time you make a change (like VMS), you need to assign it explicitly by taking an existing data set and using CATALOG to rename it as a new generation.

Here I create two versions of bar by editing the data set foo and using catalog to add a new generation by assigning to bar(+1).

edit foo
0000100 This is the first version
0000200 _end
catalog foo,u,,bar(+1)
edit foo
0000100 This is the second version
0000200 _end
catalog foo,u,,bar(+1)

We can then see the current version by accessing BAR(0) and the older version with BAR(-1) with the LINE? command, which types its contents.

line? bar(0)
0000100 THIS IS THE SECOND VERSION
line? bar(-1)
0000100 THIS IS THE FIRST VERSION

If we use, say, ERASE to delete BAR, this is seen as a partially qualified data set name (as there are two versions around) and we are prompted for each version.

erase bar
 ENTER E TO ERASE,R TO RETAIN,A TO ERASE ALL
 BAR.G0000V00
e
 BAR.G0001V00
e

It's possible to share access to data sets with other users. This is a two step process: first the owner needs to mark the data set as available using PERMIT which takes the data set name, the user list (or *ALL for all users) and a sharing specification which can be RO or RW as expected, or U for unlimited (can erase or change permissions) or R to revoke previous access. Here we make our hello world source available to all users as read only:

permit source.hworld,*all,ro

The user who wants to access this then uses SHARE to create an entry in their catalog that points to the shared data set. If you switch over to the operator console and type

share hw,tss,source.hworld

you can now access it under the name HW. The DSS? command shows this connection:

dss? hw

SYSOPER0.HW
    SHARED ACCESS: RO      OWNER: TSS*****
VOLUME: TSSRES (3330)
ORGANIZATION: VI             PAGES: 1
...

To remove this link to the shared data set, you use DELETE. ERASE would not work as this would try to remove the underlying data set, and we were granted read-only access.

erase hw
 PROCEEDING: HW                                  NOT YOURS TO ERASE.
delete hw

Here are the main commands used to manipulate data sets.

On Bitsavers, IBM Time Sharing System Concepts and Facilities introduces the concepts behind data sets and IBM Time Sharing System Command System User's Guide describes each command in more detail.

I welcome any questions or comments, and also especially any corrections if I have got something wrong. Please email me at rupert@timereshared.com and I will add it here and update the main text.