Software != Programs – Software Behaviour as an Emergent Property

What’s the Meaning of Meaning? When we talk about the behaviour of a computer program, ‘behaviour’ can have different meanings depending on the context. For example, we may consider a program as a function from input values to output values (a mathematically inspired notion); or we may consider it a construct in a logical system, and reduce it using the semantics of the programming language (a reductionist notion); or we may consider the program a collection of modules, each of which has its behaviour defined in documentation and unit-tests (a developer’s notion); or, we may consider the program a tool to render a web page or control a robot, and consider its behaviour based on its ability to perform (the customer’s and user’s notion).