Segment: ST Transaction Set Header
Position: 010
Level: Heading
Usage: Mandatory
Max Use: 1
Purpose: To indicate the start of a transaction set and to assign a control number
Syntax Notes:
Semantic Notes: 1 The transaction set identifier (ST01) is used by the translation routines of the interchange partners to select the appropriate transaction set definition (e.g., 850 selects the Purchase Order Transaction Set and the 810 selects the Invoice Transaction Set).
Notes:   Example: ST*855*0012|  
Data Element Summary 
  Ref. Data
  Des. Element Name Attributes
M ST01 143 Transaction Set Identifier Code M ID 3/3
  Code uniquely identifying a Transaction Set
  855    Purchase Order Acknowledgment
M ST02 329 Transaction Set Control Number M AN 4/9
  Identifying control number that must be unique within the transaction set functional group assigned by the originator for a transaction set
    The data interchange control number must be identical to the same data element in the associated transaction set trailer, SE02.  
855I4010 (004010) November 3, 1999