In one aspect the invention is of a method for linking separate accounts of related organizations on a commercial website which comprises establishing a tree structure defining the relationship of the various accounts in the tree, obtaining approval of the tree structure by authorized personnel responsible for the accounts, and linking the separate accounts in accordance with the relationship defined by the approved tree structure. The step of establishing a tree structure may be performed on-line. In another aspect the invention includes selecting various accounts to be linked while connected to the website, selecting at least one data parameter from a plurality of data parameters to be included in aggregated form from the selected accounts, and aggregating data for the selected data parameters from the selected accounts. In still another aspect the invention includes establishing a plurality of rules regarding the authority for users of various linked accounts to purchase goods or services from a commercial website, and assigning at least one group of users to whom the rules apply, wherein the step of establishing said plurality of rules is performed by a person representing an account at a higher level in the tree structure than the level of at least one of the accounts of the users to whom the rules apply.