Integrating with old systems.
WHAT YOU WILL MEET
Interfaces with no documentation Formats nobody remembers designing Systems nobody maintains Access only through screens or files
WHAT TO ESTABLISH FIRST
Whether a supported interface exists at all.
WHAT TO ASK FOR
Any documentation, however old Example messages Someone who remembers
WHAT TO DO WITH EXAMPLES
Treat them as the specification, and verify each assumption.
WHAT TO RECORD
Every observed behaviour, as you discover it.
WHY
It becomes the documentation that did not exist.
WHAT TO BE CAREFUL WITH
Behaviour that varies by input Fields whose meaning depends on other fields Fixed-width formats with hidden rules
WHAT TO NEVER DO
Assume undocumented behaviour is stable.
WHAT TO BUILD
Validation of everything received.
WHY
You will be the first to notice when it changes.
WHAT FILE-BASED EXCHANGE REQUIRES
A convention for naming A way to know a file is complete A record of what was processed Handling of duplicates and reruns
WHY COMPLETENESS MATTERS
Reading a file while it is being written produces partial data.
WHAT SOLVES IT
Writing elsewhere and moving, or a marker file.
WHAT TO ISOLATE
The legacy interface, behind your own.
