Basic Design (External Design)

Key points

• Basic design (external design) is the stage where, building on the system requirements, you concretely design "the parts users can see."
• It settles screen layouts, the format of reports (output documents), and how the system exchanges data with other systems (external interfaces).
• The stage that decides the program's internal structure is called "detailed design (internal design)," which follows basic design.

Where it fits within upstream process

Basic design happens right after system requirements definition, and it's the last stage of upstream process. Once basic design is finished, work moves on to "detailed design," which settles the more internal structure, and then to "implementation."

Upstream process ends here; everything after this point is downstream process.

What basic design decides

Basic design covers the parts visible from outside the system, or from the user's perspective, across three main areas.

Why it's called "external design," and how it differs from detailed design

Basic design is also called "external design" because it decides "the parts visible from the user's side." Detailed design, by contrast, is the stage that decides "the system's internal construction" — the program's structure and how data is held.

Teacher Pochi's hintIn home-building terms, basic design is the stage that decides what the people living there will actually see — the floor plan, exterior, and finishing materials — while detailed design decides the structure they'll never see, like how the framing is put together or how the wiring is routed.

A screen-design example: screen flow

Screen design also maps out "screen flow" — which screen leads to which next. This makes it concrete exactly how a user will operate the system.

Deliverable: the basic design document

The contents of basic design are compiled into a "basic design document," which records screen mockups, report layouts, and external interface specifications.

The development team uses this document to carry the work forward into detailed design and implementation. It's here that what was decided during upstream process first takes the shape of a concrete "blueprint."

Common tools used in practice

Screen design typically relies on "mockup tools" that let you check the look and feel before a single line of code is written.

Teacher Pochi's hintThis is a lot like a scale model or an architectural rendering when building a house. Being able to see roughly what it'll look like before it's real catches misunderstandings early.

Summary

Basic design (external design) takes the system requirements and turns "the parts users can see" — screens, reports, and external interfaces — into something concrete. This marks the end of upstream process; what follows is detailed design and implementation, which settle the internal structure.

Related topics:

• Business Requirements Definition
• System Requirements Definition
• Estimation Methods
• What Is Upstream Process?

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