Carnegie Mellon University Software Engineering Institute The User Interface and Software Architecture Len Bass Software Engineering Institute Carnegie Mellon University Pittsburgh PA 15213 3890 Sponsored by the U S Department of Defense 1997 by Carnegie Mellon University page 1 Carnegie Mellon University Software Engineering Institute Overview Five software qualities are important to the construction of the user interface usability buildability reusability modifiability performance Each quality has software architectural implications Qualities interact 1998 by Carnegie Mellon University page 2 Carnegie Mellon University Software Engineering Institute Usability The ability for people to learn and use a user interface quickly effectively and efficiently Architectural implications control model If user has ability to input variety of commands at any time must have structure to respond to unanticipated interrupts error handling Centralized error handling and response enables consistency feedback Feedback mechanisms both semantic and syntactic must be provided 1998 by Carnegie Mellon University page 3 Carnegie Mellon University Software Engineering Institute Buildabilty System should be constructible within reasonable cost and schedule Architectural implications use of pre existing components for user interface elements use of components with common style for API 1998 by Carnegie Mellon University page 4 Carnegie Mellon University Software Engineering Institute Reusability Using components from current system in future systems Architectural implications keep interfaces uncomplicated choose functions computed by components to be general purpose 1998 by Carnegie Mellon University page 5 Carnegie Mellon University Software Engineering Institute Modifiability Ability to easily make modifications to the user interface once it has been implemented Architectural implications separate user interface from application functionality within user interface allocate functionality based on likely pattern of changes 1998 by Carnegie Mellon University page 6 Carnegie Mellon University Software Engineering Institute Performance Provide adequate response to user input Architectural implications reduced number of interfaces reduced communication paths caching data 1998 by Carnegie Mellon University page 7 Carnegie Mellon University Software Engineering Institute Interactions Among Qualities Interactions among qualities prevent achieving all of any one quality For example performance is counter to other qualities reducing interfaces increases specificity of components and hurts reuse and modifiability buildabilty by using pre existing components hurts modifiability and usabilty reuse hurts buildability by requiring more components general and tailored usability hurts reuse by including application specific feedback and error handling 1998 by Carnegie Mellon University page 8 Carnegie Mellon University Software Engineering Institute Summary Many disputes over design are because of disagreements over priority of different qualities Can never achieve optimum result for all qualities simultaneously Must have trade offs Understanding qualities affected and interactions among them at architectural level provides structure for resolving disagreements over priorities 1998 by Carnegie Mellon University page 9