The informative material goes on to say "The modification of requirements due to approved requirement changes is covered by the "maintain" function of this specific practice; whereas, the administration of requirement changes is covered by the Requirements Management process area."
I do not understand the difference between maintenance of requirements in RD and administration of requirement changes in REQM. How are they different?
The Requirements Management (REQM) Process Area (PA) is there to help an organization manage changes to an agreed to set of requirements (baseline). So, no one makes any changes to the requirements (add/modify/delete) without following the documented requirements change control process, which should include review and approval by the relevant stakeholders of the requirements.
And actually, REQM is a specific instance of Configuration Management (CM). But REQM is such an important and vital practice that it is its own Process Area. So it is entirely possible for an organization to have one Change Management process that it uses to manage changes to requirements, documents, plans, test scripts, code, etc.
In contrast the intent of Requirements Development (RD) is to actively elicit and further refine the requirements that are then agreed to and incorporated into the requirements baseline. Specific Practice 2.1 contains the phrase “establish and maintain,” which has a special meaning within the context of the CMMI. If you have taken the Introduction to CMMI class you would have learned what this phrase means. This phrase is also defined in the CMMI Glossary and it means formulate, document, and use. For SP 2.1, this means that the product and product component requirements are formulated (elicited, discussed, refined, reviewed, etc.), documented (written down in a requirements specification, requirements management tool, etc.), and used (develop the project plan, design, code, tests, etc.).
So the connection between REQM and RD is that proposed requirements changes are reviewed, analyzed, approved, and processed by REQM and the authorized and approved changes are propagated through the baselined requirements by RD.
I would not get too focused on trying to understand the separation between REQM and RD. You have identified one of the many areas in the CMMI where there is a tight coupling between PAs, if not overlap. What is important is that you
- create a requirements baseline that does not change unless there is an approved change request,
- investigate, impact, review, and disposition all proposed requirements changes with the relevant stakeholders (approved or rejected), and
- only make approved changes to the baselined requirements and appropriately update the traceability