pabrantes,

The reason why I come up with my logic is because I think DDD should represent what happens in the real world.

And AFAIK that's what happens in the Library System.

When you go to a library where you're registered as Library User, after finding the books that interest you than you hand them over to Library Officer which do all the validations you've mentioned.

And I believe Library Officer's responsibilities are not just validate like you said but a lot more than that.

But I basically understand why you came up with your example because you just meant to simplify things and didn't really mean to address my use case.

Anyway, that's how I learn things sometimes, by trying to present my own idea and hear what people think about it, and I surely learn a lot from what you've said.

Once again, nice article, pabrantes.

Best Regards,

Setya