Which of the following standards would be least relevant for a company focusing on credit card transaction security?

Choosing the Capability Maturity Model Integration (CMMI) as the least relevant standard for a company focusing on credit card transaction security is appropriate because CMMI is primarily a process improvement framework aimed at enhancing an organization's capabilities in development and maintenance processes. It does not specifically address information security or the requirements necessary for protecting credit card transactions, which are critical for companies handling sensitive financial data.

In contrast, Payment Card Industry Data Security Standard (PCI DSS) directly focuses on securing credit card information and establishes requirements for organizations that accept, process, store, or transmit card information, making it highly relevant in this context. The General Data Protection Regulation (GDPR) also addresses data protection and privacy concerns in Europe, which include aspects that could pertain to handling payment information. Furthermore, ISO 27001 provides a framework for information security management systems (ISMS) and can encompass policies that protect sensitive data, such as credit card information.

These standards are targeted specifically at protecting sensitive financial data and ensuring compliance with regulations, making CMMI the least relevant in this specific scenario.