While it is necessary that SCIS report historical system performance, it is also necessary for the system to identify operational exceptions. Exception information is useful to highlight potential customer or operational problems. For example, proactive SCIS should be capable of identifying future inventory shortages based on forecast requirements and planned inventory. Exception reporting should also identify potential transportation, warehouse, or labor constraints. While some control measures, such as cost, are well defined, other measures, such as service and quality, are less specific. For example, customer service can be measured internally, from the enterprise's perspective, or externally, from the customer's perspective. While internal measures are relatively easy to track, information concerning external measures is more difficult to obtain, since it involves the customer or other external partners.