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A 7-digit numeric field whose first digit is the century: 0 for 1900, 1 for 2000. It was born to fit a date into very little space and cross the millennium without ambiguity, once two digits for the year were no longer enough. It costs one byte more than YYMMDD and saves one against YYYYMMDD: a trade-off still sitting inside a great many production files. Watch out for six digits: 260727 can be either YYMMDD or Julian CYYDDD, and only the file layout can tell you for sure.

In zoned decimal every digit takes a whole byte: the high nibble is F and the low one holds the digit. In packed decimal two digits share a byte, so it takes nearly half the room. In both, the last nibble carries the sign: C positive, D negative, F unsigned. The decimal point is never stored: it lives only in the field definition. This matters when you stare at a record in hex through DSPPFM and F10, or when you need to know what a file will really weigh before you create it.

Field definitions are read — name, length, type, decimals — along with the record format and key fields. Type mapping is: A to CHAR, P to DECIMAL, S to NUMERIC, L to DATE, T to TIME, Z to TIMESTAMP, B to SMALLINT, INTEGER or BIGINT depending on length. A field with no explicit type is zoned when it has decimals and character when it does not, as DDS requires. Validation keywords, default values and fields defined by reference are left out, and flagged rather than guessed: the result is a starting point to read through, not something to run blind.