Conceptual surface

From APIDesign

The term conceptual surface has been coined by Tim Boudreau during our talks about API Design. It describes the amount of concepts one needs to understand when dealing with an API. Conceptual surface metric is a very useful way to measure complexity of an API.

One common advice when it comes to separating APIvsSPI is to make sure the classes in the ClientAPI part (e.g. the conceptual surface of the API) doesn't reference the service provider part (SPI). This advice optimizes for the common case where the number of people making calls into the API (e.g. using the ClientAPI part) is an order of magnitude bigger than those providing implementation of services (e.g. ProviderAPI). Also the service provider part is often more complicated and could scary the cluelessness out of newcomers.