Seven patterns for moving DB2, IMS, and VSAM data into RAG: nightly EBCDIC export, CDC, federation, event sourcing, dual-write, schema-on-read, and RAG over the COBOL itself. Pick by freshness budget, not preference.
Modernizations die in the comprehension gap, not the rewrite. The gap has no owner, so it stays open. Five extraction patterns bind every rule to a source line, build the lineage map, and force a behavioral test suite to go green before the new system ships.