1. Agutter, C., England, R., & Van Hove, S. D. (2017). VeriSM™: A service management approach for the digital age. Van Haren Publishing.
Section 4.2.1, 'Define', Page 58: This section describes the Define stage, stating its output is "a clear understanding of the consumer, the desired outcomes, and a service blueprint". It explicitly lists "understanding the high-level requirements for the service" as a key activity. The process of understanding and documenting these requirements is what produces the definition of a good service.
2. EXIN. (2017). EXIN VeriSM™ Foundation - Preparation Guide.
Section 3.3, 'The VeriSM™ model', Page 15: The guide outlines the Define stage's purpose: "During this stage, you learn about the consumer’s needs and the high-level requirements for a product or service are defined." This confirms that defining requirements is the core process for establishing what the service should be.