Unisys DMSII

The Unisys Data Management System II ("DMSII") is a hierarchical database created by the Burroughs Corporation in 1972.

As well as having a programmatic interface to high-level languages, it has been associated with the proprietary DMInquiry and ERGO tools.

In recent releases of Unisys Clearpath software it has been renamed as the "Network Database Server".

Originally, DMS II maintained a data dictionary that the application programmer referenced in their source code. The source for the data structures was maintained in an ordinary CANDE source file. That source was then compiled with the DASDL (Data and Structure Definition Language) compiler which created the dictionary (description file) if none existed prior. If a dictionary did exist prior, then the new design indicated by the source file was incorporated into the dictionary and the programs to copy the data from the old file structure(s) and write to the new file structure(s) were automatically generated (a database reorganization task). The application programmer merely needed to re-compile his application source (typically COBOL) against the new description file and the programmer could take advantage of the new data elements in the structures.

DMSII used the concept of "Sets" for data storage. A Data Set contained rows of data and could be random or ordered. Since DMSII supported both hierarchical and relational models, a Data Set could be disjoint or embedded. Table indexes were implemented in Index Sets and could be full sets or subsets of the target Data Set. Subsets could be designated Automatic Subsets and included 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 that used field keys to reference records as well as Bit-Vectored sets that used boolean representation of set membership if the Data Set record met conditions defined in the Set.