Comprehensive and Detailed Explanation

Gap Analysis is an ADM technique used in Phases B, C, and D of the TOGAF ADM (Business, Information Systems, and Technology Architectures).

Its main purpose is to validate the target architecture by comparing the Baseline Architecture with the Target Architecture and identifying:

Gaps (building blocks or capabilities present in the target but missing in the baseline).

Overlaps (building blocks duplicated across architectures).

Conflicts (inconsistencies between baseline and target).

The output of Gap Analysis provides:

A validated Target Architecture.

A set of identified gaps that must be addressed by future work packages in Phase E: Opportunities and Solutions.

Therefore, the purpose of Gap Analysis is best expressed as to validate the architecture (Answer D).

Why the other options are incorrect

A. Establish quality metrics for the architecture: This is part of performance management and governance, not Gap Analysis.

B. Identify non-functional requirements: Non-functional requirements are captured through requirements management and stakeholder analysis, not Gap Analysis.

C. Determine service levels: Service levels are typically defined in SLAs and operational models, not through Gap Analysis.

References

The Open Group, TOGAF® Standard, Version 9.2, Part III: ADM Guidelines & Techniques — Gap Analysis.

The Open Group, TOGAF® 9 Certified Study Guide — explains the role of Gap Analysis in validating architectures and identifying work package inputs.