register schmmgmt.dll using this command
c:\windows\system32>regsvr32 schmmgmt.dll
Open mmc –> add snapin –> add Active directory schema
name it as schema.msc
Open administrative tool –> schema.msc

If a DNS server does not have an answer to a DNS request, it may be necessary to send that request to another DNS server. This is DNS forwarding.
It has two types :
1. External Forwarding
2. Conditional Forwarding

It has the following features :

• Hierarchical organization
• Extensible schema
• Centralized data storage
• Replication
• Ease of administration
• Network security
• Client configuration management
• Scalability
• Searching functionality

Dcpromo /forceremoval , an administrator can forcibly remove Active Directory and roll back the system without having to contact or replicate any locally held changes to another DC in the forest. Reboot the server then After you use the dcpromo /forceremoval command, all the remaining metadata for the demoted DC is not deleted on the surviving domain controllers, and therefore you must manually remove it by using the NTDSUTIL command.

In the event that the NTDS Settings object is not removed correctly you can use the Ntdsutil.exe utility to manually remove the NTDS Settings object. You will need the following tool: Ntdsutil.exe, Active Directory Sites and Services, Active Directory Users and Computers.

The Active Directory schema consists of rules on the types of information that can be stored within the directory. The schema is made up of two types of objects: attributes and classes.