ISSD Fall 2010 School of Information, UC Berkeley

Because requirements evolve and are refined during the design lifecycle, some early stage usability methods can only partly predict the usability of the deployed system or service. Some usability methods require a working system or prototype and the involvement of users, neither of which might be available during early stages of the design lifecycle. So there's potential conflict between software architecture - which is an early stage activity - and late stage usability efforts. Service failures occur when a service encounter falls short of the customer's expectations.