Critical success factors for purchased software should be defined from the perspective of :

Critical success factors (CSFs) for any software, particularly purchased software, are the essential outcomes that must be achieved for the software to be considered successful. These factors are fundamentally tied to the business value the software is intended to deliver. The end-users are the primary stakeholders who interact with the software to perform business tasks. Therefore, success must be defined from their perspective—does the software enable them to perform their jobs more effectively, efficiently, and with greater satisfaction? If the software fails to meet user needs and expectations, it cannot be considered successful, regardless of its technical elegance or operational stability.

B. Quality Assurance Personnel: QA personnel validate that the software meets predefined requirements; they do not define the business success criteria that form the basis of those requirements.
C. Computer Programmers: Their perspective is technical, focusing on the implementation and architecture of the software, not its ultimate business utility or user-centric success.
D. Computer Operations Personnel: They are concerned with non-functional aspects like stability and performance, which are enablers of success but not the primary measures of business value.
E. IT Management: While they oversee strategic alignment and budget, their perspective is high-level. The detailed, functional success criteria must come from those who use the software daily.

1. Sommerville, I. (2016). Software Engineering (10th ed.). Pearson. In Chapter 4, "Requirements Engineering," Section 4.1.2, it is established that a system's success is contingent on meeting the needs of its stakeholders, with users being a critical stakeholder group whose goals and tasks must be understood and supported.

2. Wiegers, K., & Beatty, J. (2013). Software Requirements (3rd ed.). Microsoft Press. Chapter 5, "Eliciting Requirements," emphasizes that the foundation of successful software is a deep understanding of user needs and business objectives, which are then translated into requirements. The success of the product is measured against these user-driven criteria.

3. ISO/IEC/IEEE 29148:2018, Systems and software engineering — Life cycle processes — Requirements engineering. This international standard specifies that the requirements process must begin with identifying stakeholders and eliciting their needs and expectations. The user is a primary stakeholder whose perspective is essential for defining what a successful system must accomplish.