Unisys DMSII
Encyclopedia
The Unisys Data Management System II (DMSII) is a database system
originally created by the Burroughs Corporation in 1972. It was available on the Burroughs (later Unisys
) Small (B1000), Medium (4000, V Series) and Large System (5000, 6000, 7000) product lines. The later, A Series, Clearpath, Libra product lines support it and in recent releases of Unisys Clearpath software it has been renamed as the Enterprise Database Server for ClearPath MCP.
It originally competed with IBM's IMS
and CICS
products and predated the popularity of relational databases.
(indexed sequential access method) model for data access, transaction isolation and database-recovery capabilities. The database schema
was written in the proprietary Data and Structure Definition Language (DASDL). The DASDL source code was compiled with a system utility into a file containing the metadata for the database (known as the description file). A database-utility program would use the database description file to create the remaining components of the database.
Proprietary language compilers (such as COBOL
and ALGOL
) would use the database description file to create database-related elements in the object code of the compiled program. These compilers used language extensions to provide a more natural interface to the database by the programmer. A number of intrinsic functions were inserted by the compiler to ensure the program and database used the same definition of database structures.
Originally, DMSII maintained a data dictionary that the application programmer referenced in its source code. The source for the data structures was maintained in an ordinary CANDE
source file. That source was then compiled with the DASDL compiler, which created the dictionary (description file) if none existed prior. If a dictionary did exist, the new design indicated by the source file was incorporated into the dictionary; 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 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 disjointed 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 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.
Database management system
A database management system is a software package with computer programs that control the creation, maintenance, and use of a database. It allows organizations to conveniently develop databases for various applications by database administrators and other specialists. A database is an integrated...
originally created by the Burroughs Corporation in 1972. It was available on the Burroughs (later Unisys
Unisys
Unisys Corporation , headquartered in Blue Bell, Pennsylvania, United States, and incorporated in Delaware, is a long established business whose core products now involves computing and networking.-History:...
) Small (B1000), Medium (4000, V Series) and Large System (5000, 6000, 7000) product lines. The later, A Series, Clearpath, Libra product lines support it and in recent releases of Unisys Clearpath software it has been renamed as the Enterprise Database Server for ClearPath MCP.
It originally competed with IBM's IMS
Information Management System
IBM Information Management System is a joint hierarchical database and information management system with extensive transaction processing capabilities.- History :...
and CICS
CICS
Customer Information Control System is a transaction server that runs primarily on IBM mainframe systems under z/OS and z/VSE.CICS is a transaction manager designed for rapid, high-volume online processing. This processing is mostly interactive , but background transactions are possible...
products and predated the popularity of relational databases.
History
DMSII provided an ISAMISAM
ISAM stands for Indexed Sequential Access Method, a method for indexing data for fast retrieval. ISAM was originally developed by IBM for mainframe computers...
(indexed sequential access method) model for data access, transaction isolation and database-recovery capabilities. The database schema
Database schema
A database schema of a database system is its structure described in a formal language supported by the database management system and refers to the organization of data to create a blueprint of how a database will be constructed...
was written in the proprietary Data and Structure Definition Language (DASDL). The DASDL source code was compiled with a system utility into a file containing the metadata for the database (known as the description file). A database-utility program would use the database description file to create the remaining components of the database.
Proprietary language compilers (such as COBOL
COBOL
COBOL is one of the oldest programming languages. Its name is an acronym for COmmon Business-Oriented Language, defining its primary domain in business, finance, and administrative systems for companies and governments....
and ALGOL
ALGOL
ALGOL is a family of imperative computer programming languages originally developed in the mid 1950s which greatly influenced many other languages and became the de facto way algorithms were described in textbooks and academic works for almost the next 30 years...
) would use the database description file to create database-related elements in the object code of the compiled program. These compilers used language extensions to provide a more natural interface to the database by the programmer. A number of intrinsic functions were inserted by the compiler to ensure the program and database used the same definition of database structures.
Originally, DMSII maintained a data dictionary that the application programmer referenced in its source code. The source for the data structures was maintained in an ordinary CANDE
CANDE
CANDE is a command line shell and text editor on the MCP operating system which runs on the Unisys Clearpath series of mainframes...
source file. That source was then compiled with the DASDL compiler, which created the dictionary (description file) if none existed prior. If a dictionary did exist, the new design indicated by the source file was incorporated into the dictionary; 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 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 disjointed 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 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
Boolean algebra
In abstract algebra, a Boolean algebra or Boolean lattice is a complemented distributive lattice. This type of algebraic structure captures essential properties of both set operations and logic operations. A Boolean algebra can be seen as a generalization of a power set algebra or a field of sets...
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
Microsoft Access
Microsoft Office Access, previously known as Microsoft Access, is a relational database management system from Microsoft that combines the relational Microsoft Jet Database Engine with a graphical user interface and software-development tools. It is a member of the Microsoft Office suite of...
), 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
Pascal (programming language)
Pascal is an influential imperative and procedural programming language, designed in 1968/9 and published in 1970 by Niklaus Wirth as a small and efficient language intended to encourage good programming practices using structured programming and data structuring.A derivative known as Object 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.