Federating a systems model

Decision records

Twenty-six records in the Nygard form, each giving the context, the decision, the alternatives considered, the consequences, the requirements affected and its sources. All twenty-six are accepted. They were written during the design phase, before any code, and copied here so that they can be read and challenged. A record’s status is accepted, or accepted, with whatever qualification the decision carries. A decision that replaces an earlier one gets its own number rather than overwriting it, and a number is never reused.

Inside the records, SR-nn is a system requirement and SC-nn a design constraint, from the set of forty-five requirements and seven constraints that From use cases to requirements describes, and a name beginning PIPE- is a short name inside the example model. C-nn is an entry on the technical constraints card, a design-phase working document that is not published, so those references are there to show what a decision rested on rather than to be looked up. The four gates the records refer to are the design phase’s own, and How the design was run says what each produced.

The shape of the system

The analysis

The adapter

The apps

The repository

AD-0026 is due for amendment when the apps ship, because the editable numbers moved to a panel above the text.