When writing a VTAM® application program, use the guidelines in Program structure recommendations to minimize the programming changes needed when:

• The application program is moved to another release of VTAM.
• The application program is moved from a single-domain environment to a multiple-domain environment.
• New SNA products or other SNA enhancements are introduced into the network.
• The VTAM application program is updated (for instance, when program temporary fixes (PTFs) are applied).