Database Files

The DB library has been constructed to provide a standard interface between the database files and application programs. Alternate means of access to database files is strongly discouraged, since file formats may change. Database files are located in the directories specified by DB (see section The Database Path).

Recall that a DB record is not a file; rather, it is an extensible collection of database files (see section Records). Thus, for example, record 100 of the MIT-BIH Arrhythmia Database consists of the files named `100.hea', `100.dat', and `100.atr' in the `mitdb' directory of the MIT-BIH Arrhythmia Database CD-ROM, together with any additional files in other directories that you may have associated with record 100 (such as your own annotation file). All files associated with a given record include the record name in their file names, either as the first part of the name (the default on writable UNIX and Macintosh file systems) or as the suffix or extension (on CD-ROM and MS-DOS file systems). Applications that use the DB library under UNIX or the Macintosh OS can locate files named using either of these conventions. No explicit action (other than choosing the file name, and locating the file in the DB path) is needed in order to associate a new file with an existing DB record.

To find the location of a database file easily, you can use `dbwhich', an application included with the DB Software Package. Type dbwhich for brief instructions on its use, or see the ECG Database Applications Guide.

File Types

There are four types of files supported by the DB library:

• Header Files: contain signal file names and attributes.
• Signal Files: contain signals.
• Annotation Files: contain annotations.
• Calibration Files: contain signal calibration specifications. The other topics in this section deal with special types of database access:
• AHA Format Files: not used for on-line DB records.
• Standard I/O: pipes and I/O redirection for DB files.
• Multiplexed Signal Files: signal groups.
• Multi-Frequency Records: signals sampled at different frequencies within within a given record.
• Multi-Segment Records: concatenated records.
• Multiple Record Access: how to have more than one record open.
• Special Files: signal I/O using block and character devices.
• Piped and Local Records: records for use with user-created signals.
• Annotation Order: the canonical order for annotations: how and why to break the rules, and how to deal with the consequences of doing so.

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