This tip continues Four Hundred Guru‘s series on the fantastic SQL enhancements that iSeries, i5 and AS/400 users received in the latest release of OS/400, which is called i5/OS V5R4. In V5R4, IBM gave developers an impressive set of Online Analytical Processing (OLAP) tools to aid with common ranking and numbering issues. The significance of these OLAP tools lies in the amount of work they do and the time it will save database programmers.

OLAP queries are generally concerned with providing answers to high level questions about large amounts of underlying data. (OLAP is also often associated with multidimensional

The following question (minus my editing for grammar) was recently posted on the IT Jungle Forums.

I have a display file that remains locked almost all day by users. If I want to recreate the file, I have to wait until all users log out, releasing the lock. Is it possible for me to recreate the display files while it is locked?

–Kaizad Patel

Those of us who still write and/or maintain green-screen applications (and there are a lot of us) understand Kaizad’s problem. Here’s my reply to him.

You can’t recreate the display file if someone has it

Similar to the PATH variable in MS-DOS and Unix, every job running on the i5/OS operating system has a library list, which tells the operating system where to locate system objects that the user is requesting. Library lists and how they are generated are basic i5/OS meat and potato issues. Nothing works without them, and it is worth understanding how they are created so that you can manipulate them to your advantage.

The Elements of a Library List

Library lists on the i5/OS and OS/400 operating systems consist of the following four components that, when grouped together, define a job’s