UCLIN is a very powerful function that must be used with extreme caution. You can use UCLIN to modify almost all the data in the SMP/E database. When you are modifying an entry, SMP/E makes sure the data within that one entry is consistent—that is, that the result could have occurred during normal SMP/E processing. However, no checking is done to make sure the resulting entry is consistent with other related entries in the database.

For example, you can use UCLIN to delete a UTILITY entry in the global zone without SMP/E detecting any error condition. However, if there is an OPTIONS entry within the global zone that refers to the deleted UTILITY entry, an error occurs when you attempt to use that OPTIONS entry. This is a very simple example of inconsistent data across entries that does not result in a serious error. UCLIN modifications to other entries, such as element, LMOD, or SYSMOD, may not be detected as error conditions during processing, but may cause incorrect processing, such as failing to link a module, updating the wrong library, or installing a SYSMOD that should not be installed.

In general, consider the following before making the UCLIN update:

1. Determine whether there is a better method of obtaining the same result. Table 1 shows where to find more information about alternatives to UCLIN.

   Table 1. Alternatives to UCLIN

   To do this without UCLIN:	Look here for more information:
   Change a common subentry in several DDDEF or UTILITY entries in the same zone	ZONEEDIT command in SMP/E for z/OS Commands
   Update the cross-zone subentries of the MOD, LMOD, and TARGETZONE entry	ZONEEDIT command in SMP/E for z/OS Commands
   Add, rename, or delete a zone	: topics on the following commands: Adding a zone: To add a zone, you can use the following commands, depending on the particular situation: ZONECOPY and ZONERNAME ZONEEXPORT, UCLIN for the ZONEINDEX and ZONEIMPORT Renaming a zone: To rename a zone, you must use the following command: ZONERENAME Deleting a zone: To delete a zone, you can use the following commands, depending on the particular situation: ZONEDELETE or ZONEEXPORT or
   Change the structure of your system (For example, to add, delete, move, or rename elements or their aliases)	z/OS Packaging Rules: topic on how to avoid UCLIN by using the appropriate MCSs and operands

2. If you are not the originator of the UCLIN, make sure you understand exactly what is being done and why. If you are not sure, find out before making the update.
3. Make sure the UCLIN is being done in the correct sequence in the process—before or after the installation of the SYSMOD.
4. Make sure all the data is correct.
5. List the entry before changing it. This makes sure you know what the original entry looked like in case an error is reported during the UCLIN or the modification causes an error.
6. After you have done all of these steps, if you have been given directions for installing the UCLIN (for example, in the PTF cover letter or in the program directory for a new function), follow those directions.