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The use of planning assistant agents is an appropriate option to provide support for members of a coalition. Planning agents can extend the human abilities and be customised to attend different kinds of activities. However, the implementation of a planning framework must also consider other important requirements for coalitions, such as the performance of collaborative activities and human-agent interaction (HAI). This paper discusses the integration of an activity-oriented planning with collaborative concepts using a constraint-based ontology for that. While the use of collaborative concepts provides a better performance to systems as a whole, a unified representation of planning and collaboration enables an easy customisation of activity handlers and the basis for a future incorporation of HAI mechanisms.