No matter how you cut it, the Customer Information System (CIS) represents a utility's largest computer asset. It eats up the most disk space. It contains the most programs and lines of code. It handles the largest volume of business, whether measured in transactions or dollars.
Billing lies at the core of the CIS. It's the most complex area. But once bills go out to customers, the CIS must manage accounts receivable and the collection process, not to mention financial control and reporting.