I’ve already written about my systems-led approach to accessibility research. This series of articles is designed to put a little more flesh on the bone with a detailed look at how OOA/OOD (Object Oriented Analysis and Design) can be used to describe computer systems and their interaction with users.
2.5 Competition for resources
When I originally began researching accessibility of user interfaces on mobile devices I focused on competition for scarce resources between individual components of the interface. An example of such competition is the use of audio channels: If the user is in a voice call, and a new text message arrives, does the “new message” ear-con play out? What if the user is recording a voice note?
Shlaer and Mellor explicitly considers such cases in terms of competition between entities to formalize relationships, and consequently allows relationships themselves to be described in terms of assigner state models, similar to the finite state machines which most object-oriented analysis and design methods such as the Unified Modelling Language (UML) , and including Shlaer and Mellor, use to describe behaviour in objects. In comparison, the industry standard use UML has no such explicit consideration of competition.
The Shlaer and Mellor approach with assigner state models is to allow the formalization of relationships to be explicitly modelled as finite state machines. There is a maximum of one instance of an assigner state model for any named association on an Information Model. Personal experience has shown this to be a very powerful technique.
Next: Transcoding of Sequences