Juha-Pekka is writing a series of articles on domain-specific modeling for DevX.com. With 15(!) years of experience in this area I suppose he definitely is an authority when it comes to DSLs, more correctly referred to as DSM languages. His second in the series deals with defining DSLs. Over the years involving many workshops, pilot projects and close co-operation with customers he has identified a number of best practices for teams in order to come to good DSM languages, as not every DSL is neccesarily a good one!