Models of Interaction

There is no silver bullet for software engineering Fred Brooks, early 1970s Everyone is talking about OOP, no one knows what it is? Tim Rentsch, 1979 Reactive systems cannot be modeled by algorithms Zohar Manna and Amir Pnueli, 1980s Concurrent systems cannot be modeled by algorithms Robin Milner, 1992 Many signs that Turing machines (TMs) cannot model OOP knowing what OO is: not possible by algorithmic models OO can be defined only by interactive models of computation Goal: negative: show OOP is not expressible by, reducible to TMs positive: unifying model for OOP, AI, networks, graphics, HCI Paradign shift from the 1970s to the 1990s: From mainframes to workstations and networks From number crunching to embedded systems and GUIs From procedures to objects and distributed systems Fundamental shift from algorithms to interactive computing 1950s-1960s: Machine language-> procedure-oriented change in the granularity of actions (scale) 1970s-1990s: Procedure-oriented-> object-based fundamental change in modeling power (quality) 1950s: machine-language programming 1960s: procedure-oriented programming 1970s: structured programming 1980s: object-based programming (single-user) 1990s: structured object-based programming with concurrency and distribution interactive, adaptable, composable scalable, heterogeneous object model dead end procedure management actions-> objects verbs-> nouns larger-granularity actions interfaces, frameworks, patterns, interoperability structure of actions (verbs) A procedure transforms arguments (inputs) to values (output) sequence of steps of procedure is an algorithm behavior is specified as a function An algorithm is a computable function from integers to integers f: X-> Y, where x∈X is completely defined prior to start Time-independent spec: indep of start time and execution time complexity: depends on number of instrs but not on time Two modes of computing: algorithms: computable functions, transformation semantics sales contracts: given an input provide an output interaction: services over time, observation semantics marriage contracts, not expressible by sales contracts formalize distinction between marriage and sales contracts Algorithms (verbs) are less expressive than objects (nouns). value (output) argument (input) procedure algorithm function function, procedure, algorithm time-independent sales contract given an input, deliver an output object, agent, actual computer marriage contract over time interactive service, interaction history closed systems, Turing machines open systems, interaction machines less expressive than