An atomic requirement is one that is self-contained and can be understood independently of other requirements or designs. It encapsulates a single piece of functionality or a single need without reference to other requirements. This characteristic ensures that the requirement can be considered, implemented, and tested on its own merits. Atomic requirements are essential for clear communication, effective analysis, and traceability throughout the project lifecycle.

Stakeholders often face challenges in prioritizing requirements due to different perceived values. This challenge arises because stakeholders may have varying opinions on what is most important, leading to conflicts and difficulties in reaching a consensus on priority. The diversity in stakeholders' backgrounds, roles, and interests can result in a wide range of perspectives on which requirements should take precedence.
References: This concept is discussed in the context of business analysis, where prioritizing requirements is a crucial step that aligns project goals with business objectives and stakeholder needs. The differences in perceived values among stakeholders are a well-known challenge in this process1.

When requirements express contractual obligations, acceptance criteria are necessary. These criteria ensure that the requirements meet the agreed-upon standards and conditions set forth in the contract. They provide a clear and measurable way to determine whether the requirements have been met satisfactorily. Acceptance criteria are used to evaluate whether the solution fulfills the contract's terms, and they form the basis for the formal acceptance of the project's deliverables. Reference: The BABOK Guide discusses the importance of acceptance criteria, especially when dealing with requirements that have contractual implications, ensuring that the deliverables meet the predefined standards and are accepted by the stakeholders1.

There are two commonly used relationships between use cases:
Extend: allows for the insertion of additional behavior into a use case. The use case that is being extended must be completely functional in its own right and must not depend on the extending use case for its successful execution. This relationship may be used to show that an alternate flow has been added to an existing use case (representing new requirements).
Include: allows for the use case to make use of functionality present in another use case. The included use case does not need to be a complete use case in its own right if it is not directly triggered by an actor. This relationship is most often used either when some shared functionality is required by several use cases or to abstract out a complex piece of logic.