This design principle suggests that the API design should support the full process of the life cycle as a single window. For instance, in an e-commerce site, when a consumer purchases an item, they shouldn't have to go to the bank portal to check their balance or to make a payment, and perhaps it should be integrated within that same e-commerce portal. The API used by the e-commerce portal should cover the full process of the life cycle. Partial, unbaked APIs severely affect the user experience.

Another aspect to think about for APIs is to provide full coverage in today's financial world; as the rapid expansion of services in cash management, automatic transfers, stock exchange orders, and so on are inevitable, APIs are the perfect solution for interconnecting these third-party services and banking services.

The same entity life cycle modelling approach that we saw earlier in the section to identify service granularity will also help us to understand which services are necessary to support the full business process life cycle.