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What should an architecture diagram explain?
Start with the reader’s question, then choose the smallest useful view. A diagram is not a complete inventory of the system: it is a scoped explanation of some part of its structure, behavior, or deployment. The C4 model organizes structural views at system, container, component, and code levels, and also describes system landscape, dynamic, and deployment diagrams. It is notation- and tooling-independent, so teams can use it without adopting a particular drawing application or visual notation.
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Choose the view by the question
- System context: orient readers to the system boundary, its users or other actors, and the external systems it interacts with.
- Container: show the major applications, services, data stores, or other deployable units within the system and their relationships.
- Component: explain the internal structure of a container when a more detailed design question warrants it.
- Code: use only when implementation-level structure is relevant to the review.
- Dynamic: show how elements collaborate during a particular behavior or scenario.
- Deployment: show where software runs when placement, infrastructure, or environment matters.
These views are options, not a checklist that every system must satisfy. Add detail when it resolves a real question; avoid expanding a diagram merely to make it look comprehensive.
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Give every diagram a descriptive title and state its intent and scope. Define acronyms, explain any notation or line styles that are not self-evident, and label relationships so readers can understand what flows or depends on what. Make arrow direction unambiguous. C4 provides diagram guidance, notation guidance, and a review checklist for evaluating clarity.
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Before sharing a diagram, ask whether a reviewer can identify the subject and boundary, distinguish internal elements from external actors, follow every important relationship, and tell what the view deliberately leaves out. If not, clarify the scope or labels rather than adding detail indiscriminately.
Which decisions belong in an ADR?
Record choices that are significant enough to affect architecture beyond a routine local implementation detail: for example, choices that are expensive to reverse, broad in scope, or risky. Not every design discussion needs its own record. arc42’s decision guidance recommends using judgment about whether a decision belongs in central architecture documentation or can remain local, and cautions against redundant records.
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An ADR should let someone who was not in the original discussion understand the forces behind the choice, the options considered, and what follows from the decision. Michael Nygard’s compact-format principle, quoted by arc42, is: “We will use a format with just a few parts, so each document is easy to digest.” Compact does not mean omitting the reasoning a reviewer needs.
A practical ADR structure
- Title: a short, specific statement of the decision topic.
- Context: neutral background, including the problem, constraints, requirements, and forces that make a choice necessary.
- Options and criteria: the alternatives considered and the criteria used to compare them. Explain why an option was rejected when that helps reviewers understand the trade-off.
- Decision: state the chosen response in active, direct language.
- Status: identify whether the record is proposed, accepted, rejected, or superseded, using statuses appropriate to the team’s process.
- Consequences: capture material positive and negative effects, including follow-up work or new constraints.
This combines the title, context, decision, status, and consequences associated with the Nygard pattern as reproduced by arc42 with explicit alternatives and decision criteria. Google Cloud’s ADR guidance also discusses options, requirements, decisions and reasons, and timestamps.
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How should teams review and maintain ADRs?
Treat an ADR as part of the decision lifecycle, not as paperwork written after the fact. AWS describes a process in which a proposal is reviewed by the team, has an owner, and is accepted or rejected. Its guidance recommends consulting ADRs during code and architecture reviews, and treating accepted or rejected records as immutable. These are useful process recommendations, not a universal standard.
- Assign an owner. Make clear who is responsible for preparing the proposal and incorporating feedback.
- Share it while the decision is still reviewable. Give relevant reviewers time to read the context, options, and criteria before the choice is finalized.
- Record the outcome. Capture acceptance or rejection, any unresolved issues or reasons for rejection, and relevant stakeholders and timestamp.
- Preserve the history. If circumstances change and an accepted decision is replaced, create a new ADR and mark the earlier one as superseded rather than rewriting its original rationale.
During a later review, compare the implementation with the recorded decision and its consequences. If the system has changed enough that the rationale no longer applies, that is a reason to revisit the choice through a new decision record—not to silently edit away the history.
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Keep the records findable
Choose a home reviewers and stakeholders can actually access. Google Cloud describes repositories, wikis, and shared documents as possible locations. For teams using docs-as-code, arc42 describes keeping plain-text documentation alongside code and reviewing changes through pull requests. A repository can make decision history visible with implementation changes; a wiki or shared document may be more accessible to non-developers. The useful choice is the one that supports both technical review and the people who need to understand the decision.
How do diagrams and ADRs work together?
A diagram shows the structure or relationship relevant to a question; an ADR explains why a consequential choice produced that structure. Link them where practical: identify the relevant diagram or system area in the ADR, and make the diagram’s scope clear enough that readers can locate related decisions. This gives a reviewer a path from what exists to the rationale behind it, without asking either artifact to do the other’s job.
Neither a particular diagram notation nor an ADR template guarantees reviewer trust. Trust comes from legible, appropriately scoped views and decision records that expose the reasoning, trade-offs, status, and history needed to assess the design.
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