Suppose that you have an application, written in C#.NET, that parses HL7 messages of type ADT^A04, also known as "Register Patient". In messages of this type, ADT indicates that the message is an Admit/Discharge/Transfer message, and A04 indicates that the patient is being registered. A Register Patient message contains all the information needed for a patient registration.

When a message of this type is received, the application needs to extract the following information:

• Patient id
• First name
• Surname
• Date of birth
• Social Security number

The application then processes the extracted data. For the purposes of this tutorial, the extracted data is just displayed on the screen.

	The choice of C#.NET is purely arbitrary and does not materially affect any of the design choices that are discussed in this tutorial.