How do the PRD, system architecture, database design, and API design work together?

How do the PRD, system architecture, database design, and API design work together?

These four documents describe different layers of the same application. The PRD defines required behavior, architecture assigns technical responsibilities, database design represents persistent information, and API design defines how application parts request and exchange that information.

Follow one feature across all four

Consider an organizer assigning a task to a collaborator. The PRD states who can assign work and what the collaborator should see. Architecture places assignment logic on the server and identifies the interface and database components involved.

Database design defines the task, wedding membership, and assignee relationship. API design specifies the assignment request, allowed fields, permission checks, and success or failure response. Each document contributes a different part of the same behavior.

Use shared language and traceable rules

Keep entity names, role names, and status values consistent. If the PRD calls a status “complete” while the API expects “finished,” the team needs an intentional translation or a naming correction.

Record important rules where they can be found and reference them across documents. A rule that assignees must belong to the same wedding should influence the form choices, server validation, and data relationship. It should not appear only as a note on a screen mockup.

Review changes across the chain

A feature change can affect more than one document. Adding event-specific tasks may require a new relationship, an API field, and an interface filter, even if the underlying architecture stays the same.

Ask AI to perform a cross-document consistency review with concrete examples. Require it to identify the conflicting passages and describe the implementation consequence. Keeping the documents aligned gives the coding assistant clearer context and helps reviewers assess whether the delivered feature matches the agreed product.