Transaction Set header (designated ST)
Transaction Set trailer (designated SE)
Single message, enveloped within the header and footer
The Transaction Set is composed of logically related pieces of information grouped into units called segments. For example, one segment used in the Transaction Set might convey the address: city, state, postal code, and other geographical information. A Transaction Set may contain multiple segments. For example, the address segment might be used repeatedly to convey multiple sets of address information.
The X12 standard defines the sequence of segments in the Transaction Set and also the sequence of elements within each segment. The relationship between segments and elements can be compared to the relationship between records and fields in a database environment. See Figure 2–7 and Figure 2–8.