Definition

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Interface

Each knew very little about the intentions and motivations of the other side, and tended to assume the worst. Messages took half a day to deliver. When they did arrive, they were couched in the opaque language of superpower diplomacy which barred the writer from admitting weakness or conceding error.
             - from One Minute to Midnight: Kennedy, Khrushchev, and Castro on the Brink of Nuclear War

One Minute to Midnight p 114

An interface is a shared boundary across which information is passed. Interfaces apply to hardware, software and human interaction. For an interface to function reliability each party to the interface must know everything "about the the intentions and motivations of the other side". Interfaces must therefore be formally specified and managed.

The figure depicts an Internet Store application with three external interfaces to internet services (Google Adds, PayPal and Google Search) and a user interface. The nature of an interface must be agreed with the organisation controlling the external system, in this case Google and PayPal. This is achieved with an interface management process. The details of an interface are specified in an Interface Control Document that is signed off by both parties.

An Application with Multiple Interfaces

Types of Interface

Interfaces should be viewed as just another component of a system. Common types are:

  • Mechanical interfaces. The physical arrangement and integration of two or more systems. For example, the mechanical fit of various electronic assemblies with marshalling cabinets and control panels
  • Data communications interfaces. The passing of information between systems by data communications transport mechanisms, protocols and network architectures
  • Human machine interfaces (user interface). The means by which human beings interact with the system
  • Electrical interfaces. The means by which systems are interconnected by electrical cabling. For example, cable specifications, hardwired connection schedules and consideration of voltage and current type, level, signal strength, impedance matching, frequency response and energy transfer constraints such as intrinsic safety
  • Electromagnetic compatibility considerations such as emission characteristics and susceptibility levels
  • Organisational interfaces. The process of negotiating the details of an interface between developing organisations or the development organisation and the Client.
Collaboration

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