"Combining elements of distinct models causes duplicate concepts and false cognates." #readingToday

Combining elements of distinct models causes two categories of problems: duplicate concepts and false cognates. Duplication of concepts means that there are two model elements (and attendant implementations) that actually represent the same concept. Every time this information changes, it has to be updated in two places with conversions. Every time new knowledge leads to a change in one of the objects, the other has to be reanalyzed and changed too. Except the reanalysis doesn't happen in reality, so the result is two versions of the same concept that follow different rules and even have different data. On top of that, the team members must learn not one but two ways of doing the same thing, along with all the ways they are being synchronized. False cognates may be slightly less common, but more insidiously harmful. This is the case when two people who are using the same term (or implemented object) think they are talking about the same thing, but really are not.

Domain-Driven Design, Eric Evans