Configuration Status Accounting (CSA) involves recording and reporting the status of configuration items throughout the lifecycle of a project. This includes:
* Status of Configuration Items: Information about the current state of items, including version numbers and change histories.
* Baselined Items: Items that have been formally approved and serve as a basis for further development.
* Changes and Updates: Documenting any modifications made to the baselined items.
CSA ensures that all stakeholders are informed about the status and history of configuration items.
References:
* "Software Configuration Management Patterns: Effective Teamwork, Practical Integration" by Stephen
P. Berczuk and Brad Appleton
* IEEE Standard for Software Configuration Management Plans (IEEE Std 828)

Disaster recovery is primarily concerned with ensuring that information systems can continue to operate or be quickly restored to operation after a disaster.
* Objective: The main objective of disaster recovery is to ensure that the system remains available, or can be quickly made available, after an interruption or disaster.
* Key Elements: This involves having backups, redundant systems, and recovery plans that can be quickly executed to restore system functionality.
* Focus on Availability: While integrity and confidentiality are also important, the immediate concern of disaster recovery is to ensure that systems are available to users to maintain business continuity.

Concurrently developing software, where multiple developers work on different parts of the codebase simultaneously, requires more rigid version control. This is because:
* Managing Changes:Ensuring that changes made by one developer do not conflict with changes made by another.
* Maintaining History:Keeping a detailed record of modifications to understand the evolution of the codebase and to revert changes if necessary.
Robust version control systems (VCS) like Git facilitate concurrent development by managing branches, merges, and conflict resolution effectively.
References:
* Version Control with Git: Powerful Tools and Techniques for Collaborative Software Development by Jon Loeliger and Matthew McCullough
* Software Configuration Management Patterns: Effective Teamwork, Practical Integration by Stephen P.
Berczuk and Brad Appleton

Functional Testing: Focuses on verifying that the software functions according to the specified requirements.
Requirements: Serve as the primary basis for functional testing, outlining what the system should do.
Design: Used in subsequent stages to ensure the system is built according to requirements.
Source Code: Tested during implementation and unit testing phases.
Architecture: Provides the high-level structure of the system but not the detailed functional behaviors.
Conclusion: The primary input to functional testing is the requirements, as these documents specify the expected functionality and behavior of the system, guiding the creation of test cases and scenarios. This aligns with standard software testing methodologies where requirementsdrive the development of functional test cases.