Author of 'Domain-Driven Design: Tackling Complexity in the Heart of Software' (2003/2004), the foundational DDD text. Coined the DDD whirlpool modeling process. In The Curse of Service Object, Ivan extracts Evans' Domain Service properties (stateless, named for an activity, representing significant business domain processes, distinct from technical services, typically with side effects) as one of the three sources of his 'service ruler'.