Item Categories and Document Types: Purchasing Information System 
You can control whether certain item categories (for example, normal, consignment) and document types (for example, a document type for purchase order is a stock transport order) are updated or not.
You can control this by allocating the item categories and/or the document types to a certain update group. An update group consists of a group of rules that determine the requirements for updating the key figures.
You can use the settings in Customizing under Purchasing. For more information, refer to the Implementation Guide.