Hold / Структура формату

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2. Структура формату

UNIMARC is designed according to an agreed set of principles. These have been adopted for UNIMARC Holdings Format.

2.1 General Structure

UNIMARC is a specific implementation of ISO 2709, an international standard that specifies the structure of records containing bibliographic data. It specifies that every bibliographic record prepared for exchange conforming to the standard must consist of:

- a Record label consisting of 24 characters;
- a Directory consisting of a 3-digit tag of each data field, along with its length and its starting character position relative to the first data field;
- Data fields of variable length, each separated by a field separator, with the following layout:
Record label Directory Data fields R/T
R/T = Record Terminator

ISO 2709 further specifies that the data in fields may optionally be preceded by indicators and subdivided into subfields. UNIMARC, as an implementation, uses the following specific options allowed under ISO 2709.

For general information on the format structure see UNIMARC Manual: Bibliographic Format, 3 Format Structure.

2.2 Functional Blocks

The fields of the holdings record are divided into functional blocks; the first (left most) digit of the tag indicates the block of the field.

0-- Identification Block: contains numbers that identify the record or the holding.
1-- Coded Information Block: contains fixed length data elements (usually coded) describing various aspects of the record or data.
2-- Location and access block: contains information that identifies the institution, physical site or collection at which a bibliographic unit is located or from which it may be available.
3-- Note Block: contains notes, intended for public display, that contribute to the identification of the item described in the holdings record.
5 --Extent of Holdings Block: contains information for caption, pattern, enumeration and chronology of a specific bibliographic item (basic or secondary unit) for which a location is to be made.
7-- Responsibility Block: contains a form of responsibility heading related to the item described in the holdings record.
8-- Source Information Block: contains the source of the record, and cataloguer's notes about the data not intended for public display.
9-- National Use Block: contains data local to the originator of the record. Field tags will not be defined in the UNIMARC Holdings Format for intersystem exchange.

2.3 Data Fields Set of Principles

(1) Tags should identify a field in two respects:

i) the type of character string (e.g., location and call number) and
ii) the function the character string performs in the record (e.g., levels).

Assigning specific values to the character positions of the tags will show these aspects. Tags may be both numeric and alphabetic. First assignment will be numeric values, expanded to alphabetic values (lower case preferred) when required.

(2) Indicators should be tag dependent but used as consistently as possible across all fields. Indicators may be both numeric and alphabetic. First assignment will be numeric values, expanded to alphabetic values (lower case preferred) when required.

(3) Subfield identifiers will be tag dependent, but, as far as possible, common data elements will be identified by the same subfield identifiers across fields. Subfield identifiers may be both numeric and alphabetic. First assignment will be alphabetic values (lower case preferred), expanded to numeric values when required. Subfield identifiers will be given values for identification rather than for file arrangement. Apart from subfield $6 which, when present, must always be the first subfield in the field, there will be no specified order for subfield identifiers, as order is determined by the data. ISO 10324 prescribes the sequence and format of data elements in order to ensure consistent recording and interpretation; however it does not prescribe the sequence in which data areas are to be displayed in a holdings statement.

(4) Descriptive information carried in notes is not intended for use as access points.

2.4 Technical Elements of Records

Content designator - The means of identifying data elements and/or providing additional information about a data element. Content designators consist of tags, indicators and subfield identifiers.

Data element - The smallest unit of information that is explicitly identified. Within a variable fie ld, a subfield identifier identifies a data element and it forms a subfield. Within the record label, directory, and fixed length subfields, the data elements are identified by their character positions.

Data element identifier - See subfield identifier.

Field - A defined character string, identified by a tag, which contains data.

Variable field - A field in which the length of an occurrence of the field is determined by the length (in characters) required to contain the data elements (including indicators, subfield identifiers, and the field separator) stored in that occurrence. The length may vary from one occurrence to the next. A variable field may contain one or more data elements or subfields.

Tag - A series of three characters used to specify the name or label of an associated field.

Indicator - A character (numeric or alphabetic) associated with a variable field that supplies additional information about the contents of the field, about the relationship between the field and other fields in the record, or about the action required in certain data manipulation processes.

Subfield - A defined unit of information within a field (see also data element).

Subfield identifier - A code consisting of two characters to identify individual subfields within a variable field. The first character is always control function 1/15 from ISO 646 and the second character is either numeric or alphabetic. Subfield identifiers are synonymous with data element identifiers.

Field separator - A control character used at the end of each variable field to separate it from the next field (control function 1/14 of ISO 646).

Record terminator - The final character in each record (control function 1/13 from ISO 646).

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