WCS | Attributes of the Product/Item | Classic Attribute Model Vs Attribute Dictionary

Attributes of the product/item are of the following types,
1. Descriptive Attributes
2. Defining Attributes

Defining Attributes: It is the attribute used for SKU resolution and on combination of multiple attributes, it resolves to an item
 Eg: If we have a product "Nike Shoes" and has the attributes of "Color" (Blue, Black) & "Size" (S, M, L). The combination of the Color and Size resolves to an item ie., for the Product "Nike Shoes", we have 6 items. So, these "Color" and "Size" has to be declared as Defining Attributes. For the "Color" attributes, the allowed values will be "Blue" & "Black" and for "Size" attribute, the allowed values will be "S", "M" & "L"

Descriptive Attributes: This attributes are not intended for any SKU Resolution. These Descriptive Attributes only provides more information about the product.
 Eg: For the HP Laptop, the Descriptive Attributes can be "Operating System Installed", "Chitset" and "Processor Speed". And the Assigned values for "Operating System Installed" might be "Windows 7" or "Windows 8" etc.

In earlier versions of WebSphere Commerce, for storing the Attributes of the products/items the following set of tables are used, which are called as "Classic Attribute Model" tables,
 - Attribute
 - Attrvalue

There are redundancy in the data that is getting stored in Class Attribute Model tables. To overcome that, IBM came up with new setup of tables and model called as "Attribute Dictionary", which will have a different normalization to avoid the redundancy of data. Here are the tables associated with Attribute Dictionary,
 - AttrDict 
 - CatentryAttr
 - Attr
 - AttrDesc
 - AttrVal
 - AttrValDesc

Here is the nice tutorial, which explains the difference between Classic Attribute Model and Attribute Dictionary,
http://publib.boulder.ibm.com/infocenter/ieduasst/v1r1m0/topic/com.ibm.iea.wcs/wcs/6.0.0.4/Customization/WCS6004_CatalogAttributeDictionary.pdf