通过将模块的接口与其实现分开，我们可以将实现的复杂性从系统的其余部分中隐藏出来。模块的用户只需要了解其接口提供的抽象。设计类和其他模块时，最重要的问题是使它们更深，以使它们具有适用于常见用例的简单接口，但仍提供重要的功能。这使隐藏的复杂性最大化。
存在语言，主要是在研究社区中，在其中可以使用规范语言来正式描述方法或功能的整体行为。可以自动检查该规范以确保它与实现相匹配。一个有趣的问题是，这样的正式规范是否可以代替接口的非正式部分。我目前的观点是，用英语描述的接口比使用正式规范语言编写的接口对开发人员来说更直观和易于理解。
By separating the interface of a module from its implementation, we can hide the complexity of the implementation from the rest of the system. Users of a module need only understand the abstraction provided by its interface. The most important issue in designing classes and other modules is to make them deep, so that they have simple interfaces for the common use cases, yet still provide significant functionality. This maximizes the amount of complexity that is concealed.
There exist languages, mostly in the research community, where the overall behavior of a method or function can be described formally using a specification language. The specification can be checked automatically to ensure that it matches the implementation. An interesting question is whether such a formal specification could replace the informal parts of an interface. My current opinion is that an interface described in English is likely to be more intuitive and understandable for developers than one written in a formal specification language.