Business data model can be represented using following diagram:

The main entites here is as the following:

User corresponds a person who registered in the system. User can have number of roles.

Role determines what operations is allowed for the user in the system.

Contract entity corresponds a single collaboration unit. It contains references to the resources related to this collaboration.

Resource holds specification of the item (product or service) that should be supplied according the contract. Each resource has one ore more tenders.

Tender is aimed to formalize the intentions to supply (Supply subclass) or consume (Need subclass) the resource by the contract's participant. Any user can add the tender to any resource. The resource owner can accept or decline posted tenders. The contract's participant is 'effective', if it's a contract creator or if it has a tender accepted by the other effective participant.

Assessment stores assessments of user activity. Assessments are made by user's partners which consumed item provided by the user.