Merrill shares his experiences during the development and implementation of a custom database management system for a large bank. He combines inverted data files (in which table fields are stored as contiguous arrays) with APL functions performing various financial modeling calculations. This allows the system to access data calculated on the fly (“virtual data”) in the same way as stored data. The evolution from a programmer’s tool to an end-user system with data consolidation, a report generator, and access to external data is described.
The paper is worth reading for current and prospective APL programmers who are interested in systems that intimately link data storage with calculations. Some size and performance comparisons to off-the-shelf DBMSs would have enhanced its value. The exposition would benefit from dividing up the long sections and from some references to related literature (both APL and non-APL).