and could be full sets or subsets of the target data set. Subsets could be designated as automatic subsets (with rules to select records from the target data set for inclusion) or manual subsets (which used programmatic interfaces to insert and remove records). Index sets included ISAM styles (which used field keys to reference records) and bit-vectored sets (which used Boolean representation of set membership if the data set record met conditions defined in the set). Like ISAM, it used sets (indexes where all records were referenced, such as the index in Microsoft Access), subsets (a partial list of records dependent upon a definable condition, e.g. females for a database with a "sex" field) and bitmaps (a set of records meeting a certain condition (true/false) on the data set). Those features achieved considerably faster performance in accessing data, with the small penalty of extra time spent on creating a new record if many subsets were defined. It was claimed that a network-type database could be built using manual-subset capability. This was risky, since it depended upon user programs to add and remove records in a manual subset. There is a substantial difference between DMSII and relational databases: in DMSII, a record can only be retrieved via an index if the index was designed initially (or after a reorganization which generates a new subset from all the data in the set). In the relational model, this is a runtime operation. In 1988 Burroughs attempted to make an object-oriented model database known as Infoexec, which was an extra layer atop DMSII. That layer was programmed in Pascal and followed the runtime-selection approach, as the relational model does. Designed by Mike Hammer and Dennis McLeod at the Massachusetts Institute of Technology, it performed poorly. See also LINC 4GL Notes Burroughs mainframe computers Unisys Proprietary database management systems Computer-related introductions in 1972 Mainframe computer software