Collection---Provider
 
 
DIF production
- Mercury: tool; Q&A to build DIF, can build DIF any other way (TECO, Perl, …) you can write text
 - GCMD: Tools plus can write text.
 - Relaxed requirements supported by both. 
 
DIF use
- Mercury: page of files to harvest; manually created/maint., used nightly.
 - GCMD: DIFs mailed, etc. Q&A, interned.