Essentials of Subfile Programming and Advanced Topics in Rpg IV

Many courses for AS/400 programmers stop short of teaching you subfile programming. Subfiles are the AS/400 tool that supports displaying lists of data on the screen, and in today's increasingly screen-based world, you must understand and be able to use them. In fact, every list that you have seen the AS/400 display has been created using the same programming techniques that you will learn in these chapters. This text introduces you to subfiles and leads you through the process of creating and debugging subfile programs. As new subfile concepts are presented, you will develop and expand the same programs to meet expanded specifications. This approach mirrors the real world in which new specifications continually add to the complexity of interactive programs. You will program interactive displays that help users find the data they need and update records as required. You will learn several techniques for designing screens that help make user displays intuitive and easy to use. In a later chapter, you'll learn to use two tools — journaling and commitment control — that will protect your database's integrity when programs let records be changed. The two ongoing sets of exercises in this text take you through the process of developing an inventory display screen and a purchase order line display screen with data maintenance capabilities. To get the most from this book, work through all segments of the continued exercises, as well as through the additional bookstore order system project that follows Chapters 5 and 7. Chapters 8 and 9 introduce Integrated Language Environment (ILE) tools for RPG. These include bound calls, multiple modules in a program, creating and using service programs, using procedures, and prototyping. Other advanced topics include using such file-oriented elements as record format level identifiers, the OVRDBF (Override with Database File) and OPNQRYF(Open Query File) CL commands, file and record locks, and file security; mining the file-information and program-status data structures for information; handling errors via the *PSSR subroutine, the INFSR keyword, and the Input/Output operation error indicator; and using data queues for program-to-program communication. Don't neglect the appendices! Appendix A explores the programming standards you'll meet in most IS departments and takes you beyond them into issues of programming style. Appendix B introduces debugging tools and techniques to support your programming skills. Finally, Appendix C gives you invaluable training in using Screen Design Aid (SDA). When you interview for a job as an AS/400 programmer, you will be asked about your knowledge of subfiles and other advanced RPG topics. Once you complete this text, its exercises, and the additional bookstore order system project, you'll have a head start on your first programming position or — if you're already a programmer — additional professional development that will count in your department and your company.

Philip J. Levinson brings more than 16 years of experience as an AS/400 programmer/analyst, consultant, and programming teacher at Jefferson College to presenting the essentials of AS/400 subfile programming. He holds a bachelor’s degree in Mechanical Engineering from the University of Hartford and a master’s degree in Management from Vanderbilt University. A member of the IBM-sponsored committee that developed the certification test for AS/400 programming, Phil lives in Olivette, Missouri, with his wife and twin sons.