Essential systems analysis was a new methodology for software specification published in 1984 by Stephen M. McMenamin and John F. Palmer for performing structured systems analysis based on the concept of event partitioning.
[2] It is an abstract model of what the system must do without describing how it will do it.
[2] The methodology[1] proposed that finding the true requirements for an information system entails the development of an essential model for the system, based on the concepts of a perfect internal technology, composed of: Edward Yourdon later adapted it to develop modern structured analysis.
[3] The main result was a new and more systematic way to develop the data-flow diagrams, which are the most characteristic tool of structured analysis.
Essential analysis, as adopted in Yourdon's modern structured analysis, was the main software development methodology until object-oriented analysis became mainstream.