Hello Gaurav,
Purchase Requisitions are linked to an Ariba Contract Workspace indirectly using Contract Terms (ACC). The primary purpose of the contract workspace is to act as a repository for all contract related documents. This also includes a link to the Contract Terms (ACC) object. The contract (ACC) is identified on the Purchase Requisition in the (contract field). Upon requisition approval, the resulting order is linked to the Contract Terms object. In, other words, spend is automatically accumulated against the contract.
In our solution, a Contract Terms object is created for each Contract Workspace. Contract Workspace header information is automatically puched to the Contract Terms object. If we want to know what requisitions are linked to a specific contract we report on the Requisition Fact and filter on the Contract dimension. I hope this helps.
It would be helpful, if you could explain the reason why you want to link Requisitions directly to a workspace.
Ken Rosehart