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Glossary of Terms

A-E

accessories

Databridge accessories access the services in DBEngine and DBSupport. Some of the accessories provided with Databridge are as follows: - DBServer, which provides communication and DMSII database replication services to Databridge Clients. - DBSpan, which produces a replication of one or more data sets into flat sequential disk files. DBSpan updates the cloned flat files by appending the changes to the end of the flat files (unlike DBSnapshot, which replaces the changed records). - DBSnapshot, which produces a one-time replication of one or more data sets into flat sequential disk files or tape. - DBInfo, which produces a report of your DMSII database timestamps, update levels, DMSII release levels, etc. - DBLister, which produces a report of the layout of the structures in your DMSII database, including structure numbers and key sets. - DBAuditTimer, which closes the current audit file when it is older than a specified length of time.

cloning

Cloning is the one-time process of generating a complete snapshot of a data set to another file. Cloning creates a static picture of a dynamic database. Databridge uses the DMSII data sets and the audit trail to ensure that the cloned data represents a synchronized snapshot of the data sets at a quiet point, even though other programs may be updating the database concurrently. Databridge clones only those data sets you specify.

Cloning is one phase of the database replication process. The other phase is tracking (or updating), which is the integration of database changes since the cloning.

CONTROL file

The DMSII CONTROL file is the runtime analog of the DESCRIPTION file. The DESCRIPTION file is updated only when you compile a modified DASDL. The CONTROL file controls database interlock. It stores audit control information and verifies that all database data files are compatible by checking the database timestamp, version timestamp, and update level. The CONTROL file is updated each time anyone opens the database for updates. The CONTROL file contains timestamps for each data set (when the data set was defined, when the data set was updated). It contains parameters such as how much memory the Accessroutines can use and titles of software such as the DMSUPPORT library (DMSUPPORT/databasename).

Databridge uses the CONTROL file for the following information:

  • Timestamps
  • INDEPENDENTRANS option
  • AFN for the current audit file and ABSN for the current audit block
  • Data set pack names
  • Audit file pack name
  • Database user code

DASDL

Data and Structure Definition Language (DASDL) is the language that defines DMSII databases. The DASDL must be compiled to create a DESCRIPTION file.

data set

A data set is a file structure in DMSII in which records are stored. It is similar to a table in a relational database. You can select the data sets you want to store in your replicated database.

Databridge Engine

The Databridge Engine (also referred to as DBEngine) is a host library program that uses the DMSII Support Library to retrieve data records from the DMSII database for cloning.

extraction

Extraction is the process of reading through a data set sequentially and writing those records to a file (either a secondary database or flat file).

R-T

replication

Replication is the ongoing process of cloning and tracking changes to a DMSII database.

set

An index into a data set. A set has an entry (key + pointer) for every record in the data set.

structure

A data set, set, subset, access, or remap. Each structure has a unique number called the structure number.

Support Library

A library that provides translation, formatting, and filtering to the DBServer and other accessories. After DBServer receives data from the Databridge Engine, it calls the Support Library to determine if the data should be replicated, and if so, passes the data to the Support Library for formatting.

tracking

Tracking is an ongoing process for propagating changes made to records in the DMSII primary database to the replicated database after the initial clone. The Databridge Engine performs extraction as well as tracking.