Give each part a reason to exist.
A module is useful when it groups a coherent responsibility. It might manage a collection of records, apply a set of business rules, or provide a shared interaction. The boundary should help people understand change rather than simply divide a codebase into smaller folders.
Architecture work begins with the tasks, concepts, and constraints that already matter to the organization. A small application may need a few well-defined internal modules rather than separate services. The appropriate structure depends on the work, the deployment environment, and the maintenance capacity.
Describe what crosses the boundary.
A connection between modules should have an understandable contract. Identify the information passed, the expected response, the conditions for a valid request, and the treatment of an unavailable dependency. These decisions make the relationship reviewable before it becomes embedded in implementation.
Potential scope includes a responsibility map, module interfaces, application structure, dependency review, and a bounded implementation. The work can also examine an existing application whose responsibilities have become difficult to distinguish.
Design for a specific kind of change.
“Easy to change” is too broad to evaluate. A project should identify which changes are likely: adding a record type, revising an approval rule, or replacing one external dependency. That context helps decide where a stable interface would be valuable.
Avoid treating every possible future need as a present requirement. A small, explained boundary is easier to assess than an elaborate abstraction built around assumptions that nobody has confirmed.
Leave a map another person can use.
A defined delivery may include a component diagram, a record of responsibilities, interface notes, and source organization appropriate to the application. It should explain the reason behind the divisions, not only list the files.
The business-module page looks more closely at how an individual responsibility can become a practical part of an application. The boundary guide examines the decisions that keep one part from quietly taking ownership of another.