MARC Records
MARC stands for Machine-Readable Cataloging formats.
MARC 21 is the current standard for the representation and communication of bibliographic and related information in machine-readable form. The MARC 21 cataloging format, as well as all official MARC 21 documentation, is maintained by the United States Library of Congress.
The MARC 21 standard uses tags to identify certain data elements in a bibliographic, authority, or holdings record. When a record is referred to as a "MARC record," it means that its variable-length data has been grouped and assigned tags in accordance with the MARC 21 standard. MARC-like records, such as MARC-like patron records, can also be imported into the Innovative database.
Each MARC record has a:
- leader
- directory
The directory is a list of variable-length fields. It contains one 12-byte entry for each field in the record. Each entry consists of the field tag (three bytes), the length of the field (four bytes) and the starting position of the field relative to the base address (five bytes). The first field in the record starts at offset 00000, i.e., the first position after the end of the directory. The directory ends with a field terminator (hex 1E).
Below is an example of a directory:001000900000 005001700009 007001500026 008004100041 028002100082 040002300103 041001100126 048000900137 100003600146 245005400182 246004400236 246006100280 246013100341 260003400472 300004000506 500001700546 500003000563 500009600593 505042800689 511007301117 650001801190 700004501208 700003701253 700004301290 700003601333 700003301369 700004501402 710004601447 791002701493 901002801520 902001101548 999002601559 993001301585 994000801598 910002001606 994001201626
The example directory above begins with the numbers "001000900000," which are interpreted as:001 Field tag number (bibliographic record control number) 0009 Length of this field (9 bytes) 00000 Starting position is the first position after the end of the directory
Another portion of the directory reads "245005400182," and is interpreted as:245 Field tag number (bibliographic record title statement) 0054 Length of this field (54 bytes) 00182 Starting position is 182 positions after the end of the directory - variable-length data
Variable-length MARC data are identified by a three-digit MARC tag stored in the directory. Each variable field begins with two positions (which can be blanks), followed by a subfield delimiter (hex 1F), a lower-case letter (usually "a") or a number, and the remaining field data. Each field ends with a field terminator (hex 1E). The last character in the record is a record terminator (hex 1D).
Variable-length MARC data can be stored in Innovative database records in either fixed-length or variable-length fields. Where information is stored depends on factors such as the decisions made by your library during implementation of the Innovative database, the load tables used when importing records, and the types of data in a record.
Innovative database variable-length fields are assigned Innovative "field group tags." The Innovative database requires the use of field group tags. MARC tags are optional. If MARC tags are used by your organization, the variable-length fields in your database will have both MARC and field group tags simultaneously. A correspondence between MARC and field group tags is established when your system is set up. For example, a MARC-tagged 090 field may have a c field group tag. You can view the expected correspondence of MARC tags and field group tags for your system by viewing the MARC load table "m2btab.fse".
For proper indexing and record display, the two types of tags must remain in the expected correspondence for each variable-length field in your database.
Changing field group tags
Depending on how your system is setup, it is possible, while editing a variable-length field, to change its field group tag and MARC tag independently of each other. This can lead to unexpected results when the field is indexed or the record is displayed. For example, if a variable-length field has a y field group tag and a 050 MARC tag, and the MARC tag is changed to 090, the field will not index with other 090 fields (which usually have a corresponding field group tag of c).
To prevent this from occurring, check the Update field group tag when MARC tagging changes option on the Editor tab in the Login Manager.