The Requirements Specification is defined in the HDF. The Requirements Analysis and Documentation process produces a set of artifacts that clearly describe the healthcare business in a given domain in terms familiar to the people who work in that business area.
Requirements Documentation is essentially a task for domain experts and analysts who represent the users. The problem space for HL7 Requirements Documentation is defined by the interaction needs of the various stake holders in a given domain of healthcare delivery. This includes all sharing of information among healthcare stake holders that may be required for the collection, aggregation, reporting, and other analysis of any clinical, administrative, and financial data information that is relevant to those stake holders.
A requirements specification defines what needs to be done, not how to do it. It is important that these two concepts not get confused. Prematurely including technical and implementation details will compromise the clarity of the original problem and will result in solutions that fall short of the business needs.