1. A computer program product comprising application software encoded on a non-transitory, tangible machine-readable storage medium, the application software being structured as process components interacting with each other through service interfaces, executing on a processor the software comprising: a plurality of process components, each of the process components comprising a modular and application-independent package of reusable granular software implementing a respective and distinct business process, the business process comprising functionality exposed by the process component via at least one service interface, the plurality of process components including: a Project Processing process component that structures, plans, and executes measures or projects; a Purchase Request Processing process component that provides a request or instruction to the purchasing department to purchase specified goods or services in specified quantities within a specified time; a Purchase Order Processing process component that handles purchase orders to external suppliers and supplier confirmations; a Purchasing Contract process component that handles agreements between purchaser and a supplier that details the supply of goods or the performance of services at agreed conditions; a Goods and Service Acknowledgement process component that handles goods and service acknowledgements, which states a recipient's obligation to pay a supplier for goods received or services rendered; a Supplier Invoice Processing process component that handles supplier invoices and supplier invoice requests; an RFQ Processing process component that handles requests for quotation and corresponding quotes; and a Time and Labor Management process component that supports the definition of employees' planned working time as well as the recording or the actual working times and absences and their evaluation; and a plurality of service interfaces, each service interface associated with exactly one process component and comprising at least one operation, each operation being implemented for exactly one process component, the operations comprising inbound and outbound operations, the outbound operation for a first process component being operable to send a message to a second process component of the plurality of process components, the second process component having an inbound operation for receiving the message, the passing of messages between an inbound and an outbound operation defining a message-based pair-wise interaction between the respective process components of the respective operations, the pair-wise interactions between pairs of the process components including interactions between: the Purchase Request Processing process component and the RFQ Processing process component, where the pair-wise interaction between the Purchase Request Processing process component and the RFQ Processing process component includes the transmission of: an RFQ execution request message from the Purchase Request Processing process component to the RFQ Processing process component, the RFQ execution request message requesting the updating of a request for quote document associated with a bidding or negotiation process; and an RFQ execution confirmation message from the RFQ Processing process component to the Purchase Request Processing process component, the RFQ execution confirmation message confirming the updating of the request for quote document; the Project Processing process component and the Purchase Request Processing process component, where the pair-wise interaction between the Project Processing process component and the Purchase Request Processing process component includes the transmission of: a Purchase Request request message from the Project Processing process component to the Purchase Request Processing, the Purchase Request request message comprising a request to modify a purchase request; and a purchase request confirmation message from the Purchase Request Processing process component to the Project Processing process component, the purchase request confirmation message confirming the modification of the purchase request; the RFQ Processing process component and the Purchase Order Processing process component, where the pair-wise interaction between the RFQ Processing process component and the Purchase Order Processing process component includes the transmission of: a supplier quote award notification message from the RFQ Processing process component to the Purchase Order Processing process component, the supplier quote award notification message providing a request to update a purchase request based on an accepted supplier quote offering to sell materials and services according to a set of requested criteria; the Purchase Order Processing process component and the Supplier Invoice Processing process component, where the pair-wise interaction between the Purchase Order Processing process component and the Supplier Invoice Processing process component includes the transmission of: an invoicing due notification message from the Purchase Order Processing process component to the Supplier Invoice Processing process component, the invoicing due notification message requesting the update of a reference object by the Supplier Invoice Processing process component to perform invoice verification with reference to a specific purchase order; and a supplier invoice request invoiced values notification message from the Supplies Invoice Processing process component to the Purchase Order Processing process component, the supplier invoice request invoiced values notification message confirming that if parts of a purchase order have previously posted that the corresponding purchase order is not changed to an amount lower than the amount that has already been delivered; the Goods and Service Acknowledgement process component and the Supplier Invoice Processing process component, where the pair-wise interaction between the Goods and Service Acknowledgement process component and the Supplier Invoice Processing process component includes the transmission of: an invoicing due notification message from the Goods and Service Acknowledgement process component to the Supplier Invoice Processing process component, the invoicing due notification message requesting the Supplier Invoice Processing process component to perform invoice verification with reference to a change associated with a purchase order for contract related invoice; and the Project Processing process component and the Time and Labor Management process component, where the pair-wise interaction between the Project Processing process component and the Time and Labor Management process component includes the transmission of: an employee time confirmation view of project notification message from the Project Processing process component to the Time and Labor Management process component, the employee time confirmation view of project notification message confirming the publishing of a project task with an assigned human resource; and a project task confirmation notification message from the Time and Labor Management process component to the Project Processing process component, the project task confirmation notification message confirming an employee's working time for a project task, including working times and additional information including status, short text, and remaining work.