The databases for which the DB library was designed consist of a small number of ECG records, each of which is quite large (typically a megabyte or more). Database records usually originate as multi-channel analog tape recordings that have been digitized and stored as disk files. For this historical reason, they are often referred to as tapes. Each record contains a continuous recording from a single subject. A typical application program accesses only a single record, and most (if not all) of the access within the record is sequential. Much less frequently, it may be of interest to compare the contents of several records, or to select sets of records. These databases are therefore qualitatively different from those for which conventional database management software is written.
Records are identified by record names, which are three-digit numbers for MIT DB records, four-digit numbers for AHA DB records, and four-digit numbers prefixed by `e' for ESC DB records. You may create database records with names containing letters, digits, and underscores. Case is significant in record names that contain letters, even in environments such as MS-DOS for which case translation is normally performed by the operating system on file names; thus `e0104' is the name of a record found in the ESC DB, whereas `E0104' is not. A record is comprised of several files, which contain signals, annotations, and specifications of signal attributes; each file belonging to a given record normally includes the record name as part of its name. (On writable UNIX and Macintosh file systems, the record name is usually the last part of the file name; the opposite convention is used on CD-ROM and MS-DOS file systems, because of their restrictions on the length of file name suffixes.) A record is an extensible collection of files, which need not all be located in the same directory, or even on the same physical device. Thus it is possible, for example, to create on a magnetic disk a file of your own annotations for a record distributed on a CD-ROM, and to treat your file as part of the record.
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