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==Theory==
CBUT is based on both software architectural views such as [[model–view–controller]] (MVC), [[presentation–abstraction–control]] (PAC), ICON and CNUCE agent models that split up the software in parts, and [[cognitive psychology]] views where a person's mental process is split up in smaller mental processes. Both software architecture and cognitive architecture use the principle of hierarchical layering, in which low level processes are more elementary and for humans often more physical in nature, such as the coordination movement of muscle groups. Processes that operate on higher level layers are more abstract and focus on a person's main goal, such as writing an application letter to get a job. The Layeredlayered Protocolprotocol Theorytheory<ref name="Farrel1999">Farrell, P.S.E., Hollands, J.G., Taylor, M.M., Gamble, H.D., (1999). Perceptual control and layered protocols in interface design: I. Fundamental concepts. ''International Journal of Human-Computer Studies'' 50 (6), 489–520. {{doi|10.1006/ijhc.1998.0259}}</ref> (LPT), which is a special version of [[Perceptualperceptual Controlcontrol Theorytheory]] (PCT), brings these views together by suggesting that users interact with a system across several layers by sending messages. Users interact with components on high layers by sending messages, such as pressing keys, to components operating on lower layers, which on their turn relay a series of these messages into a single high level message, such as 'DELETE *.*', to a component on a higher layer. Components operating on higher layers, communicate back to the user by sending messages to components operating on lower level layers. Whereas this layered-interaction model explains how the interaction is established, control loops explain the purpose of the interaction. LPT sees the purpose of the users' behaviour as the users' attempt to control their perception, in this case the state of the component they perceive. This means that users will only act if they perceive the component to be in an undesirable state. For example, if a person have an empty glass but want a full glass of water, he or she will act (e.g. walk to the tap, turning the tap on to fill the glass). The action of filling the glass will continue until the person perceives the glass as full. As interaction with components takes places on several layers, interacting with a single device can include several control loops. The amount of effort put into operating a control loop is seen as an indicator for the usability of an interaction component.
==Testing==
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