1. A computer-implemented method comprising: receiving information input by a developer through a graphical user interface, the information identifying one or more attributes of a desired input and output operation to be performed on a database table; comparing the attributes to metadata corresponding to one or more code segments included in a collection of input and output operation code segments, to identify one or more code segments for performing the desired input and output operation on the database table, the identified code segments including metadata that matches the attributes; retrieving the identified code segments for performing the desired input and output operation on the database table; analyzing metadata corresponding to one or more code segments from a collection of error handling operation code segments, to identify one or more code segments for performing an error handling operation associated with the desired input and output operation, the error handling operation identifying a particular result that will occur when an identified error occurs; retrieving the identified code segments for performing the error handing operation associated with the desired input and output operation; and automatically combining, by one or more computers, the retrieved code segments for performing the desired input and output operation on the database table with the retrieved code segments for performing the error handling operation associated with the desired input and output operation, to generate mainframe computer code.