In this chapter, three major categories of methodologies are presented: sequential, cyclical, and WaterSluice. The sequential and cyclical methodologies, informally known as the waterfall and spiral methodologies, are generic in design and have been simplified to emphasize a key aspect. In a sequential methodology, the four phase of analysis, design, implementation, and testing follow each other sequentially. In a cyclical methodology, the four phase of analysis, design, implementation, and testing are cycled with each cycle generating an incremental contribution to the final system. The WaterSluice is a hybrid borrowing the steady progress of the sequential methodology along with the iterative increments of the cyclical methodology and adds priority and governors to control change.
These three categories of methodologies form a basis for comparison. In the theory chapter, the categories are analyzed in detail. In the survey of methodology chapter, other more established methodologies, are categorized. Performance characteristics of established methodologies can be analyzed based on this categorization.
The computer software industry has introduced a major confusion in terms of naming of methodologies. The Boehm-waterfall methodology, analyzed later in this thesis, is most often quoted as a sequential methodology, but the original paper presents it as a cyclical methodology. However, in the greater computer software industry, the term waterfall has come to mean any sequential methodology. This leads to major confusion and hence the introduction, in this thesis, of the sequential classification. Likewise, the Boehm-spiral methodology, also analyzed later in this thesis, is most quoted as a cyclical methodology but behaves more like a sequential methodology with many stages. Yet the term spiral has come to mean any cyclical methodology.