A model represents a subjective interpretation by the modeler of the objective physical world. Reliability refers to a capability exhibited by an entity or system, and a reliability model is essentially a representation of this reliability as understood through human cognition. Researchers, based on their individual thinking and investigations, have developed diverse perspectives on the nature of reliability and the factors influencing it. By expressing these perspectives through quantitative or non-quantitative approaches, they have created a wide variety of reliability models. According to incomplete statistics, there are currently over 100 different software reliability models in existence.