Schema

SCHEMA:

The schema is the Active Directory component that defines all the objects and attributes that the directory service uses to store data.
The physical structure of the schema consists of the object definitions. The schema itself is stored in the directory.

Objects:

An object is the structure within which the data is stored along with the content and structure and example of an object is a User Account Object along with data regarding the syntax of the User Object. A Part of the data in an object comes from the attribute component.

Attributes:

These define the character of an object; attributes contain data that defines an object. Examples of attributes are the various properties that make up a User Account Object i.e. First Name, Last Name, Logon Name, Telephone, Location etc. Some attributes are mandatory others are not. A User Account object needs a Logon Name (Mandatory attribute) whereas an Telephone is not needed (Optional Attribute) Sometimes there is a Syntax Attribute which is linked to other attributes, the syntax attribute defines what data can be stored under other attributes. This ensures data stored within an attribute is valid.

So a collection of all there various attributes that make up the Object is the underlying framework that makes the object definition

There are few attributes which are commonly applied to any object for example the SID (Security Identifier) attribute defines the permissions to and object. So any object can use this SID attribute with just one object definition in the Schema

Classes:

Now that we understand Object definitions, it’s time to move on to classes.
Classes group various Object definitions under different categories, these are the templates that decide what attributes are needed for different objects including what are mandatory attributes and what are optional.ObjectVersion 39 – Please refer http://blogs.technet.com/b/askds/archive/2011/07/15/friday-mail-sack-peevish-nediquette-edition.aspx  

SCHEMA VERSION: