extract structured data from an ansi x12 edi 850 purchase order transaction set. capture the interchange/group/transaction envelope identifiers (ISA/GS/ST), the beginning segment (BEG) order info, the ship-to party (N1/N3/N4 with entity code ST), every PO1 line item, and the CTT line-item count. each PO1 line: LE01 is the line sequence, LE02 the quantity, LE03 the unit of measure, LE04 the unit price; the trailing qualifier/value pairs include CB (buyer item id), VN (vendor item id). lineItemCount from CTT should equal the number of PO1 lines.
