An information flow diagram (IFD) is a diagram that shows how information is communicated (or 'flows') from a source to a receiver or target (e.g. A→C), through some medium.:36–39 The medium acts as a bridge, a means of transmitting the information. Examples of media include word of mouth, radio, email, etc. The concept of IFD was initially used in radio transmission. The diagrammed system may also include feedback, a reply or response to the signal that was given out. The return paths can be two-way or bi-directional: information can flow back and forth.Peter Checkland, a British management scientist, described information flows between the different elements that compose various systems. He also defined a system as a 'community situated within an environment'.Construction of an information flow diagram requires the knowledge of different information sources and the connections between them. The sources and targets of information flow are one of the following: actor, use case, node, artefact, class, component, port, property, interface, package, activity node, activity partition, or instance specification.Limitations of information flow diagrams may include: