This paper addresses the role of Personal Digital Assistants (PDAs) in electronic meetings. Several real-world scenarios of PDA usage in meetings are defined using a pattern language. Anchored on these scenarios, we propose an upper-layer meeting middleware which addresses three major goals: defining a common architecture and set of components for meeting systems; standardizing the meeting memory and process data structures commonly managed by electronic meetings; and supporting XML-based interoperability between these components. The patterns, architecture and components were validated through their adoption in three applications, developed by different teams and covering quite different domains. The applications, encompassing several meeting patterns and adopting multifaceted combinations of the upper-layer components, demonstrate the high level of interoperability supported by the proposed upper-layer middleware.