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Concept
Unisys OS 2200 databases
Résumé
The OS 2200 database managers are all part of the Universal Data System (UDS). UDS provides a common control structure for multiple different data models. Flat files (sequential, multi-keyed indexed sequential – MSAM, and fixed-block), network (DMS), and relational (RDMS) data models all share a common locking, recovery, and clustering mechanism. OS 2200 applications can use any mixture of these data models along with the high-volume transaction file system within the same program while retaining a single common recovery mechanism.
The database managers are implemented as a protected subsystem and are called a procedure from user programs and other subsystems. The implementation as a subsystem means that there is no upper limit to the potential concurrency of activities (threads) executing in the database manager. The thread of each user executes the database manager code but within its protection domain so that misbehaved and malicious programs cannot affect the integrity of the database. This approach also reduces the path lengths and overhead involved as messages do not have to be sent between the caller and the database manager. All communication is through parameters.
This commonality has made it possible for clients to modernize applications moving from language files, to a network database, to a relational database. They can use a mixture of these at the same time in a single program while retaining full recoverability. With all the recovery, clustering, locking, and cache management centralized, applications do not have to deal with those aspects. In OS 2200 locking is generally implicit in the database verbs used. For example, a read-for-update implies setting a certain type of lock and the corresponding update write implies clearing it.
The database managers support access using many common distributed data access protocols and APIs including JDBC, OLE DB, and ODBC. See also Unisys OS 2200 distributed processing.
The heart of the database and transaction system is Integrated Recovery.
Source officielle
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