As I understand, Data Transfer Objects are used for different purposes, so let’s bound the scope with the view layer in Java (JSF) -based web-applications (i.e. there are usually some entity-objects mapped on a DB, which can be also used in a Business-Logic layer, and some transfer objects used in a presentation layer).
So, I have some misunderstanding about how should well-designed DTOs look. Should I keep them as small as possible? Or should I try to pass with them as much information as possible and design them in such way that only some (different in different use-cases) part of the DTO fields is initialized at a time?
Should I consider using some OO principles (at least inheritance and composition) when designing DTOs or they should be as simple as only a number of primitive-type fields with their accessors?
DTOs, if at all different from the domain objects/entities, should be as big as needed – you should transfer exactly all data that you need.