Control Subfields

For fields where subfield ǂu is defined as the Uniform Resource Identifier (URI), subfield ǂu contains a URI, such as a Uniform Resource Location (URL) or Uniform Resource Name (URN), which provides electronic access to a resource in a standard syntax. This information is used for automated access to an electronic item using one of the Internet protocols or by resolution of a URN. With the exception of fields 856 and 956, subfield ǂu appears with other control subfields grouped at the end of the field.

With the exceptions of fields 856, 880, 901-907, 945-949, and 956, subfield ǂu is generally used to link to value-added external or supplementary information such as audio or notational files in field 031, a table of contents in field 505, a bibliography citation in field 510, an abstract in field 520, or a description of the automated process that produced the data in fields 883 and 884. In many of these cases, subfield ǂu may be used in place of other data ordinarily found in that particular field. Do not change an existing field to remove data so that it is represented solely by a URI. Subfield ǂu may also be used to provide details to augment what is stated in other subfields.

Hexadecimal notation for diacritics and special characters. When recording a URI in subfield ǂu, you may enter most of the spacing characters listed in the table below as either characters or their hexadecimal equivalents. Do not confuse the spacing characters with their non-spacing counterparts. Use of the spacing characters will be limited almost exclusively to URLs.

Subfield ǂu defined as the URI is valid in the following fields: 031, 370, 381, 505, 506, 510, 514, 520, 530, 538, 540, 542, 545, 552, 555, 561, 563, 852, 856, 880, 883, 884, and 956. Additionally, subfield ǂu can be used in fields 901-907 and 945-949, either in accord with its control subfield definition or as a locally-defined subfield.

For fields where subfield ǂw is defined as the bibliographic record control number, subfield ǂw contains the system control number of the bibliographic resource referenced in the field. The name of subfield ǂw is Record control number in fields 760-787. The control number is preceded by the applicable MARC organization code enclosed in parentheses. See MARC Code List for Organizations, which also includes links to Canadian, United Kingdom, and German MARC organization code lists. Subfield ǂw appears with other control subfields grouped at the end of the field.

Generally include subfield ǂw only when the cited record control number relates to another bibliographic record with the same language of cataloging as indicated in field 040 subfield ǂb. For field 788, the language of cataloging must differ from the language of cataloging as indicated in field 040 subfield ǂb.

In WorldCat, subfield ǂw may be used to cite record control numbers for the Library of Congress, OCLC, national libraries, and other national level bibliographic networks. Subfield ǂw may be repeated when multiple record control numbers apply.

Do not include local system control numbers in subfield ǂw in WorldCat records.

Subfield ǂw defined as the bibliographic record control number is valid in the following fields: 760, 762, 765, 767, 770, 772, 773, 774, 775, 776, 777, 780, 785, 786, 787, 788, 800, 810, 811, 830, 880, 885, 896, 897, 898, and 899. Additionally, subfield ǂw can be used in fields 901-907 and 945-949, either in accord with its control subfield definition or as a locally-defined subfield.

Library of Congress control numbers

The Library of Congress control number (LCCN) in subfield ǂw corresponds to subfield ǂa in field 010 of the related record. The form input in subfield ǂw is a machine-readable form of the LCCN. There are differences in how the pre-2001 and post-2000 formats of the LCCN are recorded in subfield ǂw.

LCCN Pre-2001 format

• Enter the MARC organization code for the Library of Congress enclosed in parentheses, i.e., (DLC)
  
• Enter the one-to-three character prefix followed by blanks if fewer than three characters; input three blanks if there is no prefix
• Enter the two-digit year
• Omit any separating hyphens
• Input the six-digit serial number including leading zeros if the number is shorter than six digits
• Omit the trailing blank following the number
  
• Omit any trailing alphabetic identifiers and revision dates

LCCN Post-2000 format

• Enter the MARC organization code for the Library of Congress enclosed in parentheses, i.e., (DLC)
• Enter the one-to-two character prefix followed by a blank if fewer than two characters; input two blanks if there is no prefix
• Enter the four-digit year
• Omit any separating hyphens
• Input the six-digit serial number including leading zeros if the number is shorter than six digits

OCLC control numbers

• Enter the MARC organization code for OCLC enclosed in parentheses, i.e., (OCoLC)
• Omit any number signs or prefixes
  
• Enter the OCLC control number of the related record without any spaces between the designation (OCoLC) and the control number

Other control numbers

• Enter the applicable MARC organization code enclosed in parentheses, e.g., (CaOONL)
• Enter the control number of the related record without any spaces between the parenthetical designation and the control number

For fields where subfield ǂx is defined as the International Standard Serial Number (ISSN), subfield ǂx contains the ISSN for the continuing bibliographic resource referenced in the field. Enter the ISSN as two groups of four digits, separated by a hyphen. If the final character is a lowercase x, enter an uppercase X. Do not enter the caption ISSN in subfield ǂx. With the exception of fields 490 and 510 where subfield ǂx is a part of the recorded data, subfield ǂx appears with other control subfields grouped at the end of the field. For more information about the ISSN, see field 022.

Subfield ǂx defined as the ISSN is valid in the following fields: 490, 510, 534, 700, 710, 711, 730, 760, 762, 765, 767, 770, 772, 773, 774, 775, 776, 777, 780, 785, 786, 787, 788, 790, 791, 792, 793, 796, 797, 798, 799, 800, 810, 811, 830, 880, 896, 897, 898, and 899. Additionally, subfield ǂx can be used in fields 901-907 and 945-949, either in accord with its control subfield definition or as a locally-defined subfield.

For fields where subfield ǂz is defined as the International Standard Book Number (ISBN), subfield ǂz contains the ISBN for the bibliographic resource referenced in the field. Enter the 10- and/or 13-digit ISBN without any hyphens, periods, or spaces. If the final character is a lowercase x, enter an uppercase X. Omit any qualifiers or price information. Do not enter the caption ISBN in subfield ǂz. Subfield ǂz appears with other control subfields grouped at the end of the field. For more information about the ISBN, see field 020.

Subfield ǂz defined as the ISBN is valid in the following fields: 534, 556, 581, 765, 767, 770, 772, 773, 774, 775, 776, 777, 780, 785, 786, 787, and 880. Additionally, subfield ǂz can be used in fields 901-907 and 945-949, either in accord with its control subfield definition or as a locally-defined subfield.

Subfield ǂ0 contains the system control number of the related authority or classification record, or a standard identifier such as an International Standard Name Identifier (ISNI). These identifiers may be in the form of text or a URI. If the identifier is text, the control number or identifier is preceded by the applicable MARC Organization code (for a related authority record) or the Standard Identifier source code (for a standard identifier scheme), enclosed in parentheses. When the identifier is given in the form of a Web retrieval protocol, e.g., HTTP URI, no preceding parenthetical is used.

For a listing of organization codes, see MARC Code List for Organizations, which also includes links to Canadian, United Kingdom, and German MARC Organization Code lists. For a listing of standard identifiers, see Standard Identifier Source Codes. Subfield ǂ0 is repeatable for different control numbers or identifiers. Subfield ǂ0 usually appears with other control subfields grouped at the end of the field.

Include subfield ǂ0 in an access point field (1xx, 6xx, 7xx, or 8xx) only when it refers to the entity represented by the full access point.

Use of OCLC's control headings functionality in the 1xx, 7xx, and 8xx descriptive access point fields and in the 6xx subject access point fields will remove all instances of subfield ǂ0 in the case of names and subjects controlled to the LC/NACO and LCSH authority files. For access point fields where the control heading functionality is available related to other authority files, the control headings functionality will remove all instances of subfield ǂ0 other than the one linking to the authority record to which the access point is controlled.

Use of OCLC's control headings functionality is preferable to manually entering subfield ǂ0 in cases where the access point can be controlled to a particular authority file. You may enter other applicable identifiers in subfield ǂ0 such as the International Standard Name Identifier (ISNI) or the Open Researcher and Contributor ID (ORCID) in access points which are not controlled to any associated authority file record. However, such identifiers will be removed if the access point is subsequently controlled to a record in an associated authority file.

Local authority record control numbers may be entered in subfield ǂ0 locally. Do not add local authority record control numbers to WorldCat records.

Subfield ǂ0 is valid in the following fields: 022, 033, 034, 043, 050, 052, 055, 060, 070, 080, 082, 083, 084, 085, 086, 100, 110, 111, 130, 240, 251, 257, 310, 321, 334, 335, 336, 337, 338, 340, 341, 344, 345, 346, 347, 348, 353, 361, 370, 377, 380, 381, 382, 382, 384, 385, 386, 387, 388, 518, 567, 600, 610, 611, 630, 647, 648, 650, 651, 653, 654, 655, 656, 657, 658, 662, 688, 696, 697, 698, 699, 700, 710, 711, 720, 730, 751, 752, 753, 754, 758, 790, 791, 792, 793, 796, 797, 798, 799, 800, 810, 811, 830, 880, 883, 885, 896, 897, 898, and 899. Additionally, subfield ǂ0 can be used in fields 901-907 and 945-949, either in accord with its control subfield definition or as a locally-defined subfield.

Subfield ǂ1 contains a Uniform Resource Identifier (URI) that identifies an entity, sometimes referred to as a Thing or Real World Object (RWO), whether actual or conceptual. When dereferenced, the URI points to a description of that entity. A URI that identifies a name or label for an entity is contained in ǂ0.

Subfield ǂ1 is repeatable for different URIs. Subfield ǂ1 usually appears with other control subfields grouped at the end of the field.

Include subfield ǂ1 in an access point field (1xx, 6xx, 7xx, or 8xx) only when it refers to the entity represented by the full access point.

Subfield ǂ1 is valid in the following fields: 022, 033, 034, 043, 050, 052, 055, 060, 070, 080, 082, 083, 084, 085, 086, 100, 110, 111, 130, 240, 251, 257, 310, 321, 334, 335, 336, 337, 338, 340, 341, 344, 345, 346, 347, 348, 353, 361, 370, 377, 380, 381, 382, 384, 385, 386, 387, 388, 518, 567, 600, 610, 611, 630, 647, 648, 650, 651, 653, 654, 655, 656, 657, 658, 662, 690, 691, 696, 697, 698, 699, 700, 710, 711, 720, 730, 751, 752, 753, 754, 758, 790, 791, 792, 793, 796, 797, 798, 799, 800, 810, 811, 830, 880, 883, 885, 896, 897, 898, and 899. Additionally, subfield ǂ1 can be used in fields 901-907 and 945-949, either in accord with its control subfield definition or as a locally-defined subfield.

Subfield ǂ2 contains a code that identifies the source document or list from which numbers, terms, or codes appearing in the field were assigned. The name and definition of subfield ǂ2 vary slightly from field to field. Source codes are composed of lowercase alphabetic characters and, in some cases, numeric characters 0 through 9 and the hyphen. Codes vary in length, but most codes have a maximum of 12 characters. Codes are usually based on the title or numbering of the source. See Source Codes, Vocabularies, Rules, and Schemes. Subfield ǂ2 appears with other control subfields grouped at the end of the field.

The code may be followed by edition information or date of publication if the source has been published multiple times. That information is separated from the code by a slash. The omission of edition information or date of publication implies that the current version of the source was used when the record was created.

    ǂ2 msdocs/1975
    ǂ2 sears/12th

The code must be followed by an indication of language if the term appearing in the field is from a translated version of the original source document or list. The 3-character MARC language code is used when an indication of language is needed. See the MARC Code List for Languages. The language is separated from the code and any edition information or date of publication by a slash.

    ǂ2 fei/eng

Subfield ǂ2 is valid in the following fields: 015, 017, 022, 024, 026, 031, 033, 034, 041, 043, 044, 046, 047, 048, 052, 055, 072, 080, 082, 083, 084, 086, 100, 110, 111, 130, 210, 240, 251, 257, 334, 335, 336, 337, 338, 340, 341, 342, 344, 345, 346, 347, 353, 365, 366, 370, 377, 380, 381, 382, 383, 385, 386, 388, 506, 518, 520, 524, 540, 583, 600, 610, 611, 630, 647, 648, 650, 651, 654, 655, 656, 657, 658, 662, 690, 691, 695, 696, 697, 698, 699, 700, 710, 711, 730, 751, 752, 754, 758, 790, 791, 792, 793, 796, 797, 798, 799, 800, 810, 811, 830, 852, 856, 880, 885, 887, 891, 896, 897, 898, and 899. Additionally, subfield ǂ2 can be used in fields 901-907 and 945-949, either in accord with its control subfield definition or as a locally-defined subfield.

Subfield ǂ3 contains an indication of the part of the described material to which the field applies. Subfield ǂ3 appears at the beginning of the field in cases where it is intended for display, otherwise it appears with other control subfields grouped at the end of the field.

Subfield ǂ3 is valid in the following fields: 033, 034, 037, 041, 046, 050, 250, 251, 260, 264, 300, 335, 336, 337, 338, 340, 341, 344, 345, 346, 347, 351, 353, 361, 377, 380, 381, 383, 384, 385, 386, 388, 490, 500, 506, 510, 518, 520, 521, 524, 530, 533, 534, 535, 538, 540, 541, 542, 544, 546, 555, 561, 562, 563, 565, 581, 583, 584, 585, 586, 590, 600, 610, 611, 630, 647, 648, 650, 651, 654, 655, 656, 657, 690, 691, 696, 697, 698, 699, 700, 710, 711, 730, 751, 758, 773, 790, 791, 792, 793, 796, 797, 798, 799, 800, 810, 811, 830, 851, 852, 856, 880, 891, 896, 897, 898, and 899. Additionally, subfield ǂ3 can be used in fields 901-907 and 945-949, either in accord with its control subfield definition or as a locally-defined subfield.

Subfield ǂ4 contains a three-character code or URI that specifies the relationship from the entity described in the record to the entity referenced in the field. More than one relationship code or URI may be used if the named entity has more than one function. See MARC Code List for Relators. Subfield ǂ4 appears with other control subfields grouped at the end of the field.

Subfield ǂ4 is valid in the following fields: 100, 110, 111, 270, 386, 600, 610, 611, 630, 647, 648, 650, 651, 654, 662, 696, 697, 698, 699, 700, 710, 711, 720, 730, 751, 758, 760, 762, 765, 767, 770, 772, 773, 774, 775, 776, 777, 780, 785, 786, 787, 788, 790, 791, 792, 796, 797, 798, 800, 810, 811, 880, 896, 897, and 898. Additionally, subfield ǂ4 can be used in fields 901-907 and 945-949, either in accord with its control subfield definition or as a locally-defined subfield.

Subfield ǂ5 contains the code of the institution that holds the item to which the field applies. The code is used for access points and notes that do not apply to the universal description of the item or may apply universally to the item but are of limited interest. Subfield ǂ5 is used primarily for rare materials as well as for data related to special collections and projects, such as cooperative preservation programs, of interest beyond the institution creating the record. See MARC Code List for Organizations, which also includes links to Canadian, United Kingdom, and German MARC Organization Code lists. Subfield ǂ5 appears with other control subfields grouped at the end of the field.

Subfield ǂ5 is valid in the following fields: 026, 037, 246, 361, 500, 501, 506, 526, 533, 538, 540, 541, 561, 562, 563, 580, 583, 584, 585, 588, 653, 655, 700, 710, 711, 720, 730, 740, 758, 773, 774, 787, 788, 790, 791, 792, 793, 796, 797, 798, 799, 800, 810, 811, 830, 880, 885, 896, 897, 898, and 899. Additionally, subfield ǂ5 can be used in fields 901-907 and 945-949, either in accord with its control subfield definition or as a locally-defined subfield.

Other options for information specific to your institution include using Local bibliographic data (LBD), Local holdings records (LHR), or fields that are not retained in the WorldCat record. For more information, see 3.4, Local Information in Records.

Subfield ǂ6 contains data that link fields that are different script representations of the same text. Subfield ǂ6 contains the tag of an associated field and an occurrence number. It may also contain a code that identifies the first script encountered in a left-to-right scan of the field and an indication that the orientation for a display of the data is right-to-left. A variable field tag other than 880 may be linked to field 880 which contains a non-Latin script representation of the same data. Subfield ǂ6 is always the first subfield in the field.

In 2019, the scope of subfield ǂ6 was broadened in MARC 21 to allow for the recording of script identification codes taken from ISO 15924, Information and Documentation - Codes for the Representation of Names of Scripts. OCLC accommodates the four-character alphabetic codes taken from ISO 15924 in subfield ǂ6. However, OCLC does not currently accommodate the three-digit numerical codes taken from ISO 15924.

Non-Latin scripts appearing in 880 fields in a record are collectively identified in field 066.

For more information about multiscript record models and specifications for character sets, see MARC 21 Specifications for Record Structure, Character Sets, and Exchange Media.

Subfield ǂ6 is system supplied when non-Latin script is entered, and it does not appear in OCLC online displays. Do not manually add subfield ǂ6.

Subfield ǂ6 is valid in the following fields: 013, 015, 017, 018, 020, 022, 024, 026, 027, 028, 030, 031, 032, 033, 034, 035, 036, 037, 040, 041, 043, 044, 045, 046, 050, 052, 055, 072, 080, 082, 083, 084, 085, 086, 088, 100, 110, 111, 130, 210, 222, 240, 242, 243, 245, 246, 247, 250, 251, 254, 255, 256, 257, 258, 260, 263, 264, 270, 300, 306, 307, 310, 321, 334, 335, 336, 337, 338, 340, 341, 342, 343, 344, 345, 346, 347, 348, 351, 352, 353, 355, 357, 362, 363, 365, 366, 370, 377, 380, 381, 382, 383, 384, 385, 386, 388, 490, 500, 501, 502, 504, 505, 506, 507, 508, 510, 511, 513, 514, 515, 516, 518, 520, 521, 522, 524, 525, 526, 530, 532, 533, 534, 535, 536, 538, 540, 541, 542, 544, 545, 546, 547, 550, 552, 555, 556, 561, 562, 563, 565, 567, 580, 581, 583, 584, 585, 586, 588, 590, 599, 600, 610, 611, 630, 647, 648, 650, 651, 653, 654, 655, 656, 657, 658, 662, 690, 691, 696, 697, 698, 699, 700, 710, 711, 720, 730, 740, 751, 752, 753, 754, 758, 760, 762, 765, 767, 770, 772, 773, 774, 775, 776, 777, 780, 785, 786, 787, 788, 790, 791, 792, 793, 796, 797, 798, 799, 800, 810, 811, 830, 851, 852, 853, 854, 855, 856, 863, 864, 865, 866, 867, 868, 880, 882, 886, 896, 897, 898, 899, 901, 902, 903, 904, 905, 906, 907, 945, 946, 947, 948, 949, and 956.

The structure and syntax for the linkage subfield is:

ǂ6 [linking tag]-[occurrence number]/[script identification code]/[field orientation code]

Linking tag is the first data element in the subfield and is required if the subfield is used. It is the three-digit tag of the associated field.

Occurrence number is separated from the linking tag by a hyphen and is required if the subfield is used. It is a two-digit number. A different occurrence number is assigned to each set of associated fields within a record. The function of the occurrence number is to permit the matching of associated fields rather than sequencing fields within the record. An occurrence number may be assigned at random for each set of associated fields. An occurrence number of less than two digits is right justified and the unused position contains a zero.

When there is no associated Latin script field to which a field containing non-Latin script is linked, field 880 is used alone and the occurrence number in subfield ǂ6 is 00. The linking tag within subfield ǂ6 will contain the tag of the associated field if it had existed in the record.

Script identification code is used only in field 880 and is separated from the occurrence number by a slash. This code identifies the non-Latin script found in the field. The entire field does not need to be in the script identified in subfield ǂ6. If more than one script is present in the field, subfield ǂ6 will contain the identification of the first script encountered in a left-to-right scan of the field.

The following codes are used:

For scripts other than those listed above, OCLC implemented four-character alphabetic identification codes based on the ISO 15924 Code Lists.

Field orientation code is used only in field 880 and is separated from the script identification code by a slash. The contents of field 880 are always recorded in their logical order, from the first character to the last, regardless of field orientation. For display of the field, the default field orientation is left-to-right. When the field contains text that has a right-to-left orientation, field orientation code r is used.

Subfield ǂ7 contains one-character codes that indicate special characteristics of a linked entry, series access point, or availability of access to a remote electronic resource. Subfield ǂ7 contains up to four one-character codes in the case of fields 760-787, up to two one-character codes in the case of fields 800-830 and 896-899, and a single one-character code in the case of field 856. Subfield ǂ7 is named Control subfield in all fields where it occurs except field 856 where it is named Access status. In all fields except 856, subfield ǂ7 character positions are designated /0, /1, /2, etc. In current cataloging, subfield ǂ7 generally appears with other control subfields grouped at the end of the field. Subfield ǂ7 is used infrequently in fields 760-787, 800-830, and 896-899.

Except in field 856, the definition of each character position in subfield ǂ7 is dependent on the field in which it is used. Since the definitions of the codes within subfield ǂ7 are dependent on the position in which they occur, the coding of any character position after the first mandates that each preceding character position also contains a code. Succeeding character positions do not need to be coded. For example, if in fields 760-787 positions /0 and /1 are not applicable, but position /2 is, then positions /0 and /1 contain code n.

Subfield ǂ7 is valid in the following fields: 361, 720, 760, 762, 765, 767, 770, 772, 773, 774, 775, 776, 777, 780, 785, 786, 787, 800, 810, 811, 830, 856, 880, 896, 897, 898, and 899. Additionally, subfield ǂ7 can be used in fields 901-907 and 945-949, either in accord with its control subfield definition or as a locally-defined subfield.

Although MARC 21 also defines subfield ǂ7 for use in field 533, OCLC has implemented that subfield as field 539.

Fields 760-787

Up to four character positions that indicate special characteristics of the linked entry defined as follows:

/0 - Type of main entry heading. Code indicating either the type of name contained in subfield ǂa or the preferred title in subfield ǂt. The codes correspond to the 1xx field in the record for the related item, i.e., field 100 for personal names, field 110 for corporate names, field 111 for meeting names, and field 130 for preferred titles. Code n is used when no other codes apply.

p	Personal name
c	Corporate name
m	Meeting name
u	Uniform title
n	Not applicable

/1 - Form of name. Code indicating the form of the name contained in subfield ǂa. The code corresponds to the value of the 1st indicator in the 1xx field in the record for the related item, and must be interpreted in conjunction with the value in position /0.

For position /0 coded p, position /1 contains one of the following codes:

0	Forename
1	Surname
3	Family name

For position /0 coded c or m, position /1 contains one of the following codes:

0	Inverted name
1	Jurisdiction name
2	Name in direct order

For position /0 coded u or n, position /1 contains the following code:

n	Not applicable

/2 - Type of record. Code indicating the type of record for the related item. The code corresponds to the code in Type in the record for the related item.

a	Language material
c	Notated music
d	Manuscript notated music
e	Cartographic material
f	Manuscript cartographic material
g	Projected medium
i	Nonmusical sound recording
j	Musical sound recording
k	Two-dimensional nonprojectable graphic
m	Computer file
o	Kit
p	Mixed material
r	Three-dimensional artifact or naturally occurring object
t	Manuscript language material

/3 - Bibliographic level. Code indicating the bibliographic level of the related item. The code corresponds to the code in BLvl in the record for the related item.

a	Monographic component part
b	Serial component part
c	Collection
d	Subunit
i	Integrating resource
m	Monograph/item
s	Serial

Fields 800-830 and 896-899

Up to two character positions that indicate special characteristics of the access point defined as follows:

/0 - Type of record. Code indicating the type of record for the related item. The code corresponds to the code in Type in the record for the related item. Codes d, f, and t are unlikely to be used in position /0.

a	Language material
c	Notated music
d	Manuscript notated music
e	Cartographic material
f	Manuscript cartographic material
g	Projected medium
i	Nonmusical sound recording
j	Musical sound recording
k	Two-dimensional nonprojectable graphic
m	Computer file
o	Kit
p	Mixed material
r	Three-dimensional artifact or naturally occurring object
t	Manuscript language material

/1 - Bibliographic level. Code indicating the bibliographic level of the related item. The code corresponds to the code in BLvl in the record for the related item. Codes a, b, c, d, and i are unlikely to be used in position /1.

a	Monographic component part
b	Serial component part
c	Collection
d	Subunit
i	Integrating resource
m	Monograph/item
s	Serial

Field 856

A single one-character code indicating the availability of access to the remote electronic resource specified in subfield ǂu. For more information, see field 856.

Subfield ǂ8 identifies linked fields and may also propose a sequence for the linked fields. Subfield ǂ8 may be repeated to link a field to more than one other group of fields. You are responsible for creating and maintaining links in subfield ǂ8. The system does not create or maintain these links. Subfield ǂ8 generally appears at the beginning of the field.

Subfield ǂ8 is valid in the following fields: 010, 013, 015, 016, 017, 018, 020, 022, 024, 025, 026, 027, 028, 030, 031, 032, 033, 034, 035, 036, 037, 040, 041, 043, 044, 045, 046, 047, 048, 050, 051, 052, 055, 060, 061, 070, 071, 072, 074, 080, 082, 083, 084, 085, 086, 088, 100, 110, 111, 130, 210, 222, 240, 242, 243, 245, 246, 247, 250, 251, 254, 255, 256, 257, 258, 260, 263, 264, 270, 300, 306, 307, 310, 321, 334, 335, 336, 337, 338, 340, 341, 342, 343, 344, 345, 346, 347, 348, 351, 352, 353, 355, 357, 361, 362, 363, 365, 366, 370, 377, 380, 381, 382, 383, 384, 385, 386, 388, 490, 500, 501, 502, 504, 505, 506, 507, 508, 510, 511, 513, 514, 515, 516, 518, 520, 521, 522, 524, 525, 526, 530, 532, 533, 534, 535, 536, 538, 540, 541, 542, 544, 545, 546, 547, 550, 552, 555, 556, 561, 562, 563, 565, 567, 580, 581, 583, 584, 585, 586, 588, 590, 599, 600, 610, 611, 630, 647, 648, 650, 651, 653, 654, 655, 656, 657, 658, 662, 690, 691, 696, 697, 698, 699, 700, 710, 711, 720, 730, 740, 751, 752, 753, 754, 758, 760, 762, 765, 767, 770, 772, 773, 774, 775, 776, 777, 780, 785, 786, 787, 788, 790, 791, 792, 793, 796, 797, 798, 799, 800, 810, 811, 830, 850, 852, 856, 880, 882, 883, 891, 896, 897, 898, and 899. Additionally, subfield ǂ8 can be used in field 886, either in accord with its control subfield definition or its foreign MARC subfield definition. Subfield ǂ8 can be used in fields 901-907 and 945-949, either in accord with its control subfield definition or as a locally-defined subfield.

The structure and syntax for the field link and sequence number subfield is:

ǂ8 [linking number].[sequence number]\[field link type]

Note that subfield ǂ8 is defined differently in field 852 where it is used to sequence related holdings records.

Linking number is the first data element in the subfield and required if the subfield is used. It is a variable-length whole number that occurs in subfield ǂ8 in all fields that are to be linked. Fields with the same linking number are considered linked.

Sequence number is separated from the linking number by a period and is optional. It is a variable-length whole number that may be used to indicate the relative order for display of the linked fields with lower sequence numbers displaying before higher ones. If it is used, it must occur in all subfields ǂ8 containing the same linking number.

Field link type is separated from preceding data by a reverse slash. It is a code used to indicate the reason for the link and it follows the link number or the sequence number when the sequence number is present. Field link type is required except when subfield ǂ8 is used to link and sequence 84x-87x holdings fields. The following one-character field link type codes have been defined for use in subfield ǂ8:

For fields where subfield ǂ9 is defined as special entry, subfield ǂ9 contains user-specified information.

Subfield ǂ9 defined as special entry is valid in the following fields: 690, 691, 696, 697, 698, 699, 796, 797, 798, 799, 880, 896, 897, 898, and 899. Additionally, subfield ǂ9 can be used in fields 901-907 and 945-949, either in accord with its control subfield definition or as a locally-defined subfield.

Subfield ǂe is valid only in field 856.

Subfield ǂl is valid in the following fields: 760, 762, 765, 767, 770, 772, 773, 774, 775, 776, 777, 780, 785, 786, 787, 788.

Subfield ǂy is valid in the following fields: 533, 800, 810, 811, 830.

Subfield ǂ7 is valid in the following fields: 041, 082, 083, 084, 100, 110, 111, 130, 210, 240, 245, 246, 247, 250, 255, 256, 264, 300, 335, 336, 340, 348, 370, 377, 380, 381, 382, 383, 384, 385, 386, 387, 388, 490, 500, 501, 502, 505, 508, 510, 515, 518, 520, 546, 550, 555, 583, 600, 610, 611, 630, 648, 650, 651, 653, 655, 700, 710, 711, and 751.