Data mappers Vs Data Managers

In context of PHP MVC frameworks, what is the role of Data Mappers and Data Managers. How do they differ or what are their common responsibilities.

Based on what I have read from different sources, mappers transform a DTO to an object representing database entity and managers transform a DTO to a business entity. So will I have separate classes for representing plain data as DTO, its DB version and its business version and then separate classes for conversions.