EA Domain Layers
The four conventional layers of enterprise architecture — business, data, application and technology — each answering a different question about the estate.
The layering exists so that a change can be traced through its consequences rather than assessed in one place.
Business architecture — capabilities, processes, value streams, organisational structure. What the business does and how it is arranged to do it.
Data architecture — the information the enterprise holds, who owns each domain, how it flows, and what governs it.
Application architecture — the systems that support the capabilities, their responsibilities and their integrations.
Technology architecture — the infrastructure, platforms and standards those applications run on.
The value is entirely in the traceability between layers, not in the layers themselves. Being able to answer "which capabilities does this platform support, and therefore what does its retirement affect" is the point. A set of four unconnected inventories is a filing exercise.
The failure mode that makes enterprise architecture unpopular: modelling for completeness rather than for a question. A full model of every layer at fine granularity takes years, is stale on delivery, and answers nothing anyone asked.
The alternative that works: model to the depth a specific decision requires — a rationalisation programme, a migration, a compliance obligation — and let the model grow from real questions rather than from a framework's table of contents.