Clean Architecture: A Craftsman's Guide to Software Structure and Design

19POLICY AND LEVEL

Software systems are statements of policy. Indeed, at its core, that’s all a computer program actually is. A computer program is a detailed description of the policy by which inputs are transformed into outputs.

In most nontrivial systems, that policy can be broken down into many different smaller statements of policy. Some of those statements will describe how particular business rules are to be calculated. Others will describe how certain reports are to be formatted. Still others will describe how input data are to be validated.

Part of the art of developing a software architecture is carefully separating those policies from ...