Active Directory® Schema is a Microsoft Management Console (MMC) snap-in that you can use to view and manage the Active Directory Domain Services (AD DS) schema.
You can also use the Active Directory Schema snap-in to view and manage Active Directory Lightweight Directory Services (AD LDS) schema objects.
The schema contains formal definitions of every object class that can be created in an Active Directory forest. The schema also contains formal definitions of every attribute that can or must exist in an Active Directory object.
The Active Directory Schema snap-in includes two containers: the Classes container and the Attributes container. These containers store the class and attribute definitions. These definitions take the form of classSchema objects, which you can view in the Classes container, and attributeSchema objects, which you can view in the Attributes container.
Making changes to the AD DS schema is advisable only rarely. Errors in schema changes can result in data loss and corruption. For this reason, before you attempt any manipulation of schema objects, be sure that you understand the effects of the change and that you have deployed the change and observed its effects in a test forest.
Before making any schema changes, read the Active Directory Schema Technical Reference (http://go.microsoft.com/fwlink/?LinkID=65961). For information about how to make schema changes, see Active Directory Schema (http://go.microsoft.com/fwlink/?LinkId=80809).