1. A system comprising: a computer system comprising one or more hardware platforms for executing computer software; computer software deployed on the computer system, the computer software implementing a plurality of service operations, the service operations comprising: a change project based on purchase request confirmation operation operable to send a confirmation to a requester of the extent to which a requisition has been fulfilled; a change project based on purchase order operation operable to notify the project about the creation of a purchase order for an external resource; a change project based on employee time calendar operation operable to send a confirmation of working time for a project task; a check task availability for accounting operation operable to notify of task availability; a request service operation operable to request a buyer to procure external resources or services; a notify of project operation operable to inform accounting about a creation or change of project elements; a request project cost estimate operation operable to inform accounting about a creation or change of project elements that are costing relevant; a request project cost estimate simulation operation operable to request to perform a synchronous project costing simulation; a query project cost estimate operation operable to query costing for the last costing result for project elements; a create accounting entry operation operable to receive an accounting document from another instance of accounting; a maintain subledger account operation operable to receive a project accounting notification from project processing; a create accounting document operation operable to receive an expense accounting notification from expense and reimbursement processing; a synchronous valuate product and resource operation operable to synchronize access to price information for products; a maintain project cost estimate operation operable to inform costing document processing about the creation or change of project elements that are costing relevant; a cancel accounting document operation operable to receive an expense accounting notification from expense and reimbursement processing; and a simulate project cost estimate operation operable to request performance of a synchronous project costing simulation and response.