The method is based on the progressive development of a theoretical model grounded initially in the literature and then refined using case studies grounded in practice.

In each case cycle the researcher seeks to refine the current version of the theoretical model by:

• looking for reinforcement of concepts already contained within the theoretical model
• revelation – identifying new areas for exploration and potential reinforcement
• learning and reflection on data collected so far
• re-examining previous transcripts for further reinforcement of emerging themes


The researcher is active in the data collection. Leading questions are encouraged in order to facilitate reinforcement and semi-structured, open-ended questions are used to facilitate revelation. Exploration of these revelations is incorporated into revised interview scripts which are used in the next cycle. Reinforced concepts are retained in the evolving theoretical model. The process is ongoing but concluded when there has been enough reinforcement for a representative model of the research domain being investigated to stand alone or when theoretical saturation has been reached. Therefore, the outcome of the research method is a revised theoretical model (with several revisions during the process) which represents a theory which has evolved about the area being investigated.

The paper uses an illustrative study of the use of models in object-oriented requirements engineering to demonstrate the use of the evolutionary case approach. The final theoretical model of object-oriented requirements engineering reinforced the concept of three processes of elicitation, modeling and validation and revealed the importance of mental models at the elicitation stage and the need to develop separate informal models for clients and formal models for implementers.