I believe the PBL is a community of practice.
The Domain Is the shared interest by the group members to complete a given assignment, their Domain
The Community is all the members of the group sharing their knowledge, research and skills to build their group’s relationships, their Community
The Practice The final product, whether it be a powerpoint presentation, an oral presentation, an information report etc. becomes their practice and they have learnt to problem solve, how to complete a particular text of project and are able to take this experience into work into future projects, their Practice.
Smith. M. (2009). Communities of practice. Retrieved from http://www.infed.org/biblio/communities_of_practice.htm