Release 10.1A: OpenEdge Getting Started:
Database Essentials

> ## OpenEdge database file structure

> The OpenEdge database contains more than data. Figure 3–1 illustrates the components of an OpenEdge database. Descriptions of the files follow.

> Figure 3–1: OpenEdge RDBMS

> As shown in Figure 3–1, a typical OpenEdge database consists of:

> - A structure description (.`st`) file, which defines the database’s structure. The .`st` file is a text file with a .`st` filename extension. The administration utility PROSTRCT CREATE uses the information in the `.st` file to create the database’s areas and extents. It is the database administrator’s responsibility to create the `.st` file. See OpenEdge Data Management: Database Administration for detailed information about structure description files.

> - A log (`.lg`) file, which is a text file. The .`lg` file contains a history of significant database events, including server startup and shutdown, client login and logout, and maintenence activity.

> - One database (.`db`) control area, which is a binary file containing a database structure extent. The control area and its .`db` file act as a table of contents for the database engine, listing the name and location of every area and extent in the database.

> - One primary recovery (before image) area, which contains one or more extents with a .`b` `n` filename extension. The .`bi``` file stores notes about data changes. In the event of hardware failure, the database engine uses these notes to undo any incomplete transactions and maintain data integrity.

> - One schema area, which contains at least one variable-length extent with a .`d` `n` filename extension. The schema area contains the master and sequence blocks, as well as schema tables and indexes. Progress Software Corporation recommends that you place all your application data in additional data areas, but if you do not create application data areas, the schema area contains your user data.

> - Optionally, application data areas, which contain at least one variable-length extent with a .`d` `n` filename extension. Application data areas contain user data, indexes, clobs and blobs.

> - Optionally, one after-image (.`ai`) area when after-imaging is enabled. The after-image area can contain many fixed-length and variable-length extents with the .`a` `n` filename extension. In the event of hardware failure, the database engine uses the .`a` `n` file and the most recent backup to reconstruct the database.

> - Optionally, one transaction log (.`tl`) area when two-phase commit is in use. It contains one or more fixed-length extents with the .`t` `n` filename extension; variable-length extents are not allowed. The transaction log lists committed two-phase commit transactions.

> An OpenEdge database means collectively all the files described above: the control area, schema area, data areas, recovery files, and log files. You should treat these files as an indivisible unit. For example, the phrase “back up the database” means “back up the database data, .`lg`, .`d` `n`, .`tl`, .`ai`, and .`bi` files together.”

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