====== Schema Extensions ======
https://carlstanley.com/how-to-create-a-custom-attribute-in-active-directory/

Object Identifiers
^ OID Value                                                                     ^ Description   ^
| 1.2.840.113556.1.8000.2554.13459.24689.17637.19755.40171.2749453.4868242      | Root          |
| 1.2.840.113556.1.8000.2554.13459.24689.17637.19755.40171.2749453.4868242.1    | Classes       |
| 1.2.840.113556.1.8000.2554.13459.24689.17637.19755.40171.2749453.4868242.2    | Attributes    |
| 1.2.840.113556.1.8000.2554.13459.24689.17637.19755.40171.2749453.4868242.2.1  | personNumber  |
| 1.2.840.113556.1.8000.2554.13459.24689.17637.19755.40171.2749453.4868242.2.2  | pin           |


Your root OID is: 
1.2.840.113556.1.8000.2554.13459.24689.17637.19755.40171.2749453.4868242

This prefix should be used to name your schema attributes and classes. For example: if your prefix is "Microsoft", you should name schema elements like "microsoft-Employee-ShoeSize". For more information on the prefix, view the Schema Naming Rules in the server Application Specification (http://www.microsoft.com/windowsserver2003/partners/isvs/appspec.mspx).

You can create subsequent OIDs for new schema classes and attributes by appending a .X to the OID where X may be any number that you choose.  A common schema extension scheme generally uses the following structure:
If your assigned OID was: 1.2.840.113556.1.8000.2554.999999

then classes could be under: 1.2.840.113556.1.8000.2554.999999.1 
which makes the first class OID: 1.2.840.113556.1.8000.2554.999999.1.1
the second class OID: 1.2.840.113556.1.8000.2554.999999.1.2     etc...

Using this example attributes could be under: 1.2.840.113556.1.8000.2554.999999.2 
which makes the first attribute OID: 1.2.840.113556.1.8000.2554.999999.2.1 
the second attribute OID: 1.2.840.113556.1.8000.2554.999999.2.2     etc...

Here are some other useful links regarding AD schema:
Understanding AD Schema
http://technet2.microsoft.com/WindowsServer/en/Library/b7b5b74f-e6df-42f6-a928-e52979a512011033.mspx 

Developer documentation on AD Schema:
http://msdn2.microsoft.com/en-us/library/ms675085.aspx 

Extending the Schema
http://msdn2.microsoft.com/en-us/library/ms676900.aspx 

Step-by-Step Guide to Using Active Directory Schema and Display Specifiers 
http://www.microsoft.com/technet/prodtechnol/windows2000serv/technologies/activedirectory/howto/adschema.mspx 

Troubleshooting AD Schema 
http://technet2.microsoft.com/WindowsServer/en/Library/6008f7bf-80de-4fc0-ae3e-51eda0d7ab651033.mspx