Chapter Fifteen. Distillation






Chapter Fifteen. Distillation

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These four equations, along with the definitions of their terms and the body of mathematics they rest on, express the entirety of classical nineteenth-century electromagnetism.

James Clerk Maxwell, A Treatise on Electricity and Magnetism, 1873

How do you focus on your central problem and keep from drowning in a sea of side issues? A LAYERED ARCHITECTURE separates domain concepts from the technical logic that makes a computer system run, but in a large system, even the isolated domain may be unmanageably complex.

Distillation is the process of separating the components of a mixture to extract the essence in a form that makes it more valuable and useful. A model is a distillation of knowledge. With every refactoring to deeper insight, we abstract some crucial aspect of domain knowledge and priorities. Now, stepping back for a strategic view, this chapter looks at ways to distinguish broad swaths of the model and distill the domain model as a whole.

As with many chemical distillations, the separated by-products are themselves made more valuable by the distillation process (as GENERIC SUBDOMAINS and COHERENT MECHANISMS), but the effort is motivated by the desire to extract that one particularly valuable part, the part that distinguishes our software and makes it worth building: the "CORE DOMAIN."

Strategic distillation of a domain model does all of the following:

  1. Aids all team members in grasping the overall design of the system and how it fits together

  2. Facilitates communication by identifying a core model of manageable size to enter the UBIQUITOUS LANGUAGE

  3. Guides refactoring

  4. Focuses work on areas of the model with the most value

  5. Guides outsourcing, use of off-the-shelf components, and decisions about assignments

This chapter lays out a systematic approach to strategic distillation of the CORE DOMAIN, and it explains how to effectively share a view of it within the team and provides the language to talk about what we are doing.

1. A navigation map for strategic distillation

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Like a gardener pruning a tree, clearing the way for the growth of the main branches, we are going to apply a suite of techniques to hew away distractions in the model and focus our attention on the part that matters most. . . .


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