So far, you have learned how to generate HL7 messages containing non-repeating and repeating segments. In some cases, however, you may want to generate an HL7 message in which entire groups of segments repeat.

For instance, the segment grammar of the sample message you have been using in this tutorial is:

MSH PID OBR {OBX}

Here, {OBX} indicates that the OBX segment can be repeated an unlimited number of times.

In this section of the tutorial, you will alter the segment grammar to be the following:

MSH PID {OBR {OBX}}

In this segment grammar, OBR {OBX} represents a segment group consisting of an OBR segment followed by any number of OBX segments. {OBR {OBX}} indicates that any number of these segment groups may be present in the message. Here are some examples of segment sequences matching this segment grammar:

MSH PID OBR OBX OBX OBR OBX OBX OBX
MSH PID OBR OBX
MSH PID OBR OBX OBX OBX 
MSH PID OBR OBX OBR OBX OBR OBX OBR OBX

As the second and third examples show, the messages matching the old segment grammar also match the new grammar.

In the following sections of this tutorial, you will take the VMD file you have constructed and modify it to handle a potentially unlimited number of OBR {OBX} segment groups. To do this, you must:

• Modify the message's segment grammar to allow repeating segment groups.
• Modify the message's table grammar to reflect the changes in the segment grammar.
• Update the table mappings.
• Regenerate the stubcode and application.
• Test the new mappings.