My Coolest Code


What’s the coolest code you’ve written, for your own definition of cool?

EDI: the Worst Document Format?

From 2003-2006 I worked at a startup building enterprise software for the health care space. We were building a system which allowed doctors offices to submit real-time transactions over the Internet, to migrate offices away from phone, fax or mail. Our first step was allowing real-time inquiry for insurance eligibility and benefits of a patient. Each doctor’s office runs an EMR (“Electronic Medical Records”) system. When John Doe walks into his doctor’s office, they call his insurance company to determine co-pays, etc. With our system, the EMR could do this automatically in seconds.

The industry has an standard format for this request, known as X12 270. It looks like this:


The corresponding response is known as X12 271. The doctor’s EMR would submit a 270 document to us, we’d need to parse it, pass the data to the BigHealthInsuranceCo, get the response back and convert that response into a 271 document to return to the EMR.

So a quick rundown:

Oh, EDI documents are also called transactions so, yay confusion! I’m going to stick to calling them documents.

The Problem

The core difficulty we needed to solve: how the hell do we parse the above gobblygook into an object format we can easily CRUD? Keep in mind, the 270 document is about the simplest document format – it gets way, way more complex – so using regular expressions to parse were out of the question.

But “parse” is the key word here.

I realized we needed to go up a level of abstraction and get a machine-readable description of each EDI document format so we could build a parser. This is when I discovered SEF descriptors. Each document type (270, 271, etc) has an associated SEF descriptor which describes the specific EDI document format. The essence of what I’m so proud of is this:

a JavaCC grammar for parsing SEF files and generating a JavaBeans object model so we can parse specific EDI documents, manipulate the JavaBeans and emit an updated, well-formed document

I got something bare bones working after a month or so; soon we had full support for 270, 271, 835, 837p, 837i and other health related transactions.

The Solution

Here’s the code! Keep in mind that all of this code and data is almost 20 years old, I put it on GitHub purely for my own historical interest.

I read the SEF document format standard in sef16.pdf and built a JavaCC grammar for it.

Here’s an old 270 SEF. Once I had the grammar, I could use JavaCC to parse the SEF for each document type and emit Java code which knew how to parse an EDI 270 InputStream into a set of Java beans. With a set of JavaBeans which described the document, the sky was the limit – we could write any business logic the customer needed.

The Conclusion

So instead of maintaining a massive set of horrid regexps, I maintained the SEF grammar and JavaBeans generator. If we needed a new feature for the various document types, I could implement it and regenerate the JavaBeans, giving all document types that new feature. If we needed to support a new X12 document type, I just grabbed the SEF for it and generated the associated beans. Typically it would take me hours rather than months.

Behold, the power of an abstraction layer. That’s pretty cool.


I haven’t written Java in 15 years. I saw Ruby on Rails in 2005 and fell in love with Ruby.

These days I believe X12 has been superceded by the HL7 standard which uses XML and therefore is easy to parse. EDI should be relegated to the dustbin of legacy formats ASAP.