Informal Definition of Scalability

Scalability is a nonfunctional requirement that almost every product should possess. But specifically which metrics should you use to define it? A simple (and informal) definition of scalability is:

"More and more of it while still satisfying the other requirements."

You then must ask, "More of what?" And, "How much more?"

The Wikipedia entry for "scalability" mentions three forms:

load
geographic
administrative

Answer these questions in measurable terms, and you've defined the scalability requirements for your product.

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