Input–output model

An input–output model describes a computation by specifying the outputs produced for supplied inputs, without necessarily detailing the internal steps.

Function (mathematics): A relation that assigns each element of a domain exactly one element of a codomain. A deterministic input–output model can be represented as a function from inputs to outputs.
Input–output relation: A relation that associates possible inputs with possible outputs, allowing multiple outcomes for one input. It generalizes a function when the computation can produce several valid outputs.
Application programming interface: A defined interface through which software components exchange requests and responses. An API exposes a computation as operations with specified inputs and outputs.
Operational semantics: A formal account of programming-language meaning defined by the steps of computation. It specifies internal execution steps where an input–output model may leave them abstract.
Domain of a function: The set of inputs for which a function is defined. It specifies which supplied values the model accepts.
State machine: A computational model whose transitions depend on its current state and an input. For stateful computations, outputs depend on interaction history as well as the latest input.
Unit testing: Software testing that checks a small, isolated unit of code against expected behavior. Tests commonly compare outputs with expected results for chosen inputs.
Denotational semantics: A method of defining program meaning by mapping expressions to mathematical objects. It gives a semantic mapping that may capture more structure than input–output behavior alone.
Codomain: The set in which a function's outputs are specified to lie. It describes the possible output space of a function-based model.
Mealy machine: A finite-state machine whose outputs are associated with transitions triggered by inputs. It makes input–output behavior explicit for systems that respond over time.

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