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>>The fields (segments) can map to whatever field in the data tables. They are in fixed position in the HL7 data (text) stream. Meaning, I may not always have 7 rows, but when I see "PDI" at the beginning of a line, I know that there will be x number of fields to follow. Many will be empty, but the delimiters will still be there. It may be more complex than that - haven't read Greg's reply yet - but for the billing piece I'm working on at the moment, I think that's pretty much it.
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>A segment is an entire line...for example, you would call it a PID segment, if it starts with PID. The segment contains fields, which are most likely called "elements".
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>In EDI, there is a larger subdivision called a transaction set (or a document). So, for example, a purchase order document will be mapped to purchase order header records and line item records (and perhaps other tables, too). But the information that will go into the order header record is spanned across multiple segments (lines, not fields) in the EDI document. The purchase order number comes from a segment starting with "BEG". The requested ship date in a DTM segment. Shipto location in N1 segment. And so on.
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>So does each HL7 segment map to one record in a table? Or do several HL7 segments work together to map to a record in a table?

As much as I know at this point, there will be a process run on each message after it is parsed out and put into cursor to update the tables. I believe it's simply updating a couple data tables based on the patient number, diagnosis codes, etc. I may be missing the boat because this just seems like a pretty straight forward mapping fields to fields kind of thing once I get the HL7 data stream message and parse it out. I must be wrong though because many others seem to think there's more to it. We are only working with one vendor at the moment, though we have many client's they all use this vendor with our software, so the format is the same each message. Maybe if we had multiple vendors and had to handle that, it would be more involved. If what I'm doing is more involved than I think, I would really like to know now so I can update my project timelines accordingly.