Design approaches

In a smaller system, the design of the entire system can be shown in one place.

This class diagram of se-edu/addressbook-level2 depicts the design of the entire software.

The design of bigger systems needs to be done/shown at multiple levels.

This architecture diagram of se-edu/addressbook-level3 depicts the high-level design of the software.

Here are examples of lower level designs of some components of the same software:

UI

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Logic

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Storage

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Multi-level design can be done in a top-down manner, bottom-up manner, or as a mix.

• Top-down: Design the high-level design first and flesh out the lower levels later. This is especially useful when designing big and novel systems where the high-level design needs to be stable before lower levels can be designed.
• Bottom-up: Design lower level components first and put them together to create the higher-level systems later. This is not usually scalable for bigger systems. One instance where this approach might work is when designing a variation of an existing system or re-purposing existing components to build a new system.
• Mix: Design the top levels using the top-down approach but switch to a bottom-up approach when designing the bottom levels.