AWS Directory Service
Administration Guide (Version 1.0)

Active Directory Schema

A schema is the definition of attributes and classes that are part of a distributed directory and is similar to fields and tables in a database. Schemas include a set of rules which determine the type and format of data that can be added or included in the database. The User class is one example of a class that is stored in the database. Some example of User class attributes can include the user’s first name, last name, phone number, and so on.

Schema Elements

Attributes, classes and objects are the basic elements that are used to build object definitions in the schema. The following provides details about schema elements that are important to know before you begin the process to extend your AWS Managed Microsoft AD schema.


Each schema attribute, which is similar to a field in a database, has several properties that define the characteristics of the attribute. For example, the property used by LDAP clients to read and write the attribute is LDAPDisplayName. The LDAPDisplayName property must be unique across all attributes and classes. For a complete list of attribute characteristics, see Characteristics of Attributes on the MSDN website. For additional guidance on how to create a new attribute, see Defining a New Attribute on the MSDN website.


The classes are analogous to tables in a database and also have several properties to be defined. For example, the objectClassCategory defines the class category. For a complete list of class characteristics, see Characteristics of Object Classes on the MSDN website. For more information about how to create a new class, see Defining a New Class on the MSDN website.

Object identifier (OID)

Each class and attribute must have an OID that is unique for all of your objects. Software vendors must obtain their own OID to ensure uniqueness. Uniqueness avoids conflicts when the same attribute is used by more than one application for different purposes. To ensure uniqueness, you can obtain a root OID from an ISO Name Registration Authority. Alternatively, you can obtain a base OID from Microsoft. For more information about OIDs and how to obtain them, see Object Identifiers on the MSDN website.

Schema linked attributes

Some attributes are linked between two classes with forward and back links. The best example is groups. When you look at a group it shows you the members of the group; if you look at a user you can see what groups it belongs to. When you add a user to a group, Active Directory creates a forward link to the group. Then Active Directory adds a back link from the group to the user. A unique link ID must be generated when creating an attribute that will be linked. For more information, see Linked Attributes on the MSDN website.

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