23. Graphs of the old and new systems

The methodology replaces this manual work with three structured records, each fixed for the length of the project. The Source-state ontology is a graph of the old system, built from the legacy code by agents: its files, classes, functions, statements and APIs. The Source-state ontology keeps the actual code statements, as evidence of the behavior the new system must reproduce. The Target-state ontology is a graph of the new system, built from the target blueprint: its architecture, runtime, standards and design system. The specification connects the two graphs, and produces a requirements document, test scenarios, end-to-end test scripts and a chatbot that answers questions about the code. The Product Owner and Architect mark every module of the old system, in the specification, with one of four decisions. Retain keeps the module's behavior while its structure changes. Modify changes the behavior in defined ways that the Product Owner records. Replace hands the function to a different solution, such as a modern library. Retire removes the function, and the retired items stay documented. A module without a decision cannot be migrated.

On the site: The Three Modernization Ontologies · The Source-State Ontology in Detail · The Target-State Ontology in Detail