In today,s complex bussiness enviroment the proprietary AS/400-iSeries “IBMi” system is a solution for manage customers in companies , i use Client Access , Commands in the Control Language (CL) are promptable using the keyboard F4 function key. The most useful are
- WRKSPLF – Work with spooled files
- WRKQRY- Work with Queries
- CPYF, CRTF, DSPF, CHGF, DLTF – Copy, create, display, change, and delete file
About payments is possible insert the information and generate a file whit the amount, if the client in debt or is up to date, in my case a use for generate invoice payment,, all infformation is a unique database
Support for 5250 display operations is provided via display files, an interface between workstations, keyboards and displays, and interactive applications, as opposed to batch processing with little or no user interaction
the configuration of 5250( terminal) configuration 
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Tables in AS/400
