A Data Transfer Object is an object that is used to encapsulate data, and send it from one layer/system to another.
It reduces the amount of data that needs to be sent across the layer.
When we prefer not to send Domain objects to the consuming service we choose DTO with selected data to filter out unnecassary data to prevent it from being shared.
DTOs are called Data Transfer Objects because their whole purpose is to shift data in expensive remote calls
Some people argue for them as part of a Service Layer API because they ensure that service layer clients aren’t dependent upon an underlying Domain Model. While that may be handy, I don’t think it’s worth the cost of all of that data mapping. As my contributor Randy Stafford says in P of EAA Don't underestimate the cost of [using DTOs].... It's significant, and it's painful
