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Library of Congress >> MARC >> Understanding MARC
Part I: What Does MARC Mean?
Part II: Why Is a MARC Record Necessary?
Part III: MARC Terms and Their Definitions
Part IV: Where do MARC Records Originate?
Part V: MARC Data Issues
Part VI: In Conclusion
It is impossible these days to read a library journal, attend a library conference, or even have an informal chat with other librarians without hearing the phrases 'MARC format,' 'MARC records,' or 'MARC-compatible.' Many library professionals have not had an opportunity to take formal courses explaining the important topics of library automation and the role of MARC, yet automated library systems may be important parts of their libraries.
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This booklet will explain -- in the simplest terms possible -- what a MARC record is, and it will provide the basic information needed to understand and evaluate a MARC record.
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Part I:
What Does MARC Mean?
What is a MARC record? A MARC record is a MA chine-Readable Cataloging record.
And what is a machine-readable cataloging record?
Machine-readable: 'Machine-readable' means that one particular type of machine, a computer, can read and interpret the data in the cataloging record. The following pages will explain why this is important and how it is made possible.
Cataloging record: 'Cataloging record' means a bibliographic record, or the information traditionally shown on a catalog card. The record includes (not necessarily in this order): 1) a description of the item, 2) main entry and added entries, 3) subject headings, and 4) the classification or call number. (MARC records often contain much additional information.)
1) Description: Librarians follow the rules in Anglo-American Cataloguing Rules, 2nd ed., 2002 revision to compose the bibliographic description of a library item. This 'description' is shown in the paragraph sections of a card. It includes the title, statement of responsibility, edition, material specific details, publication information, physical description, series, notes, and standard numbers.
2) Main entry and added entries: AACR2 also contains rules for determining 'access points' to the record (usually referred to as the 'main entry' and 'other added entries'), and the form these access points should take. Access points are the retrieval points in the library catalog where patrons should be able to look up the item.
In other words, the rules in AACR2 are used to answer questions such as: For this book, should there be entries in the catalog for more than one author or more than one title? Should the title of the series be noted? How should the author's name be written? Is this a 'title main entry' item (no author)?
3) Subject headings (subject added entries): The librarian uses the Sears List of Subject Headings (Sears), the Library of Congress Subject Headings (LCSH), or some other list of standard subject headings to select the subjects under which the item will be listed. Use of an approved list is important for consistency, to ensure that all items on a particular subject are found under the same heading and therefore in the same place in the catalog.
For instance, the subject heading list indicates that all books about cats should be assigned the subject CATS. Using this authorized heading eliminates the possibility of listing some books under CATS and others under FELINES. Even if a book is called All About Felines, the subject heading will be typed CATS. That way, all books on that subject will be listed in one place in the catalog for the patron to find. The patron does not have to imagine all the possible synonyms for the word he is looking for.
4) Call number: The librarian uses a Dewey Decimal or Library of Congress classification schedule to select the call number for an item. The purpose of the call number is to place items on the same subject together on the same shelf in the library. Most items are sub-arranged alphabetically by author. The second part of the call number usually represents the author's name, facilitating this subarrangement.
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Part II:
Why Is a MARC Record Necessary?
Why can't a computer just read a catalog card? The information from a catalog card cannot simply be typed into a computer to produce an automated catalog. The computer needs a means of interpreting the information found on a cataloging record. The MARC record contains a guide to its data, or little 'signposts,' before each piece of bibliographic information.
The place provided for each of these pieces of bibliographic information (author, title, call number, etc.) is called a 'field.' The records in simpler computer files sometimes have a fixed number of fields, and each field contains a fixed number of characters.
However, to allow proper cataloging of books and other library items, the best file structure allows for records with an unlimited number of fields and unlimited field lengths. This flexibility is necessary because not all titles are the same length (The robe versus Alexander and the terrible, horrible, no good, very bad day). Some books are part of a series, requiring a field for that information, while others have no series statement. And audiovisual items have much longer physical descriptions (5 filmstrips : sd., col. ; 35 mm. + teaching manual) than do most books (403 p. : ill. ; 22 cm.).
The computer cannot expect a certain type of information to begin and end at the same position in every bibliographic record. The statement of responsibility will not always begin with the 145th character of the record and end at the 207th position, for example. Therefore each MARC record contains a little 'table of contents' to the record, according to a predefined standard.
Data 'signposts:' The computer must have assistance if it is to read and interpret the bibliographic record. The box charts on the right illustrate the information these 'signposts' need to convey.
If a bibliographic record has been marked correctly and saved in a computer data file, computer programs can then be written to punctuate and format the information correctly for printing a set of catalog cards, or for displaying the information on a computer screen. Programs can be written to search for and retrieve certain types of information within specific fields, and also to display lists of items meeting the search criteria.
Why one standard? You could devise your own method of organizing the bibliographic information, but you would be isolating your library, limiting its options, and creating much more work for yourself. Using the MARC standard prevents duplication of work and allows libraries to better share bibliographic resources. Choosing to use MARC enables libraries to acquire cataloging data that is predictable and reliable. If a library were to develop a 'home-grown' system that did not use MARC records, it would not be taking advantage of an industry-wide standard whose primary purpose is to foster communication of information.
Using the MARC standard also enables libraries to make use of commercially available library automation systems to manage library operations. Many systems are available for libraries of all sizes and are designed to work with the MARC format. Systems are maintained and improved by the vendor so that libraries can benefit from the latest advances in computer technology. The MARC standard also allows libraries to replace one system with another with the assurance that their data will still be compatible.
MARC 21: The Library of Congress serves as the official depository of United States publications and is a primary source of cataloging records for US and international publications. When the Library of Congress began to use computers in the 1960s, it devised the LC MARC format, a system of using brief numbers, letters, and symbols within the cataloging record itself to mark different types of information. The original LC MARC format evolved into MARC 21 and has become the standard used by most library computer programs. The MARC 21 bibliographic format, as well as all official MARC 21 documentation, is maintained by the Library of Congress. It is published as MARC 21 Format for Bibliographic Data.
A comparison of the same record with textual information and with MARC tags illustrates the compactness of the MARC 21 format. It's a matter of storage space. Look at the box charts below . The MARC 21 format uses '260' '$a' '$b' and '$c' to mark the field that holds imprint data instead of storing the words 'publication area,' 'place of publication,' 'name of publisher,' and 'date of publication' in each record. This convention makes more efficient use of computer storage space.
Record with textual 'signposts'
| 'SIGNPOSTS' | DATA |
|---|---|
| Arnosky, Jim. |
| Raccoons and ripe corn / Jim Arnosky. |
| 1st ed. |
| New York : Lothrop, Lee & Shepard Books, c1987. |
| 25 p. : col. ill. ; 26 cm. |
| Hungry raccoons feast at night in a field of ripe corn. |
| Raccoons. |
| Local call number: | 599.74 ARN |
| Local barcode number: | 8009 |
| Local price: | $15.00 |
Same record with MARC tags
| 'SIGNPOSTS' | DATA | |||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Arnosky, Jim. Raccoons and ripe corn / Jim Arnosky. 1st ed. New York : Lothrop, Lee & Shepard Books, c1987. 25 p. : col. ill. ; 26 cm. Hungry raccoons feast at night in a field of ripe corn. Raccoons. 599.74 ARN 8009 $15.00 |
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Part III:
MARC Terms and Their Definitions
This section covers how to read, understand, and use a MARC record. It deals with what librarians using a library automation system will see and need to understand on their computer screens when adding, editing, or examining records. The emphasis will be on those areas commonly used in cataloging for schools and small public libraries, i.e. books and audiovisual materials. However, what is covered in this section applies equally to all forms of materials, including sound recordings, computer software, maps, and other non-book items.
Recently approved changes, some of which have already been implemented, to the MARC 21 bibliographic format have involved the concept of Format Integration. 'Format Integration' means that the same 'signposts' are used to mark data in records for all types of publications, rather than having different sets of 'signposts' for each type. More technically, under Format Integration, one group of tags is used for records of all types of materials rather than having a tag set defined for each type.
The box chart in the previous section showed a MARC record labelled with 'signposts.' The proper names of these 'signposts' are field, tag, indicator, subfield, subfield code, and content designator. These MARC 21 terms are covered in this section.
1. FIELDS are marked by TAGS.
A field: Each bibliographic record is divided logically into fields. There is a field for the author, a field for title information, and so on. These fields are subdivided into one or more 'subfields.' As previously noted, the textual names of the fields are too lengthy to be reproduced within each MARC record. Instead they are represented by 3-digit tags. (Though online catalogs may display the names of the fields, the names are supplied by the system software, not by the MARC record.)
A tag: Each field is associated with a 3-digit number called a 'tag.' A tag identifies the field -- the kind of data -- that follows. Even though a printout or screen display may show the tag immediately followed by indicators (making it appear to be a 4- or 5-digit number), the tag is always the first 3 digits.
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The tags used most frequently are:
| 010 tag | marks the Library of Congress Control Number (LCCN) |
| 020 tag | marks the International Standard Book Number (ISBN) |
| 100 tag | marks a personal name main entry (author) |
| 245 tag | marks the title information (which includes the title, other title information, and the statement of responsibility) |
| 250 tag | marks the edition |
| 260 tag | marks the publication information |
| 300 tag | marks the physical description (often referred to as the 'collation' when describing books) |
| 490 tag | marks the series statement |
| 520 tag | marks the annotation or summary note |
| 650 tag | marks a topical subject heading |
| 700 tag | marks a personal name added entry (joint author, editor, or illustrator) |
Here is an example of a field. The number 100 is the tag, defining it as a personal name main entry (author) field.
The Cataloging Distribution Service of the Library of Congress distributes a detailed listing of all tags in both the 2-volume publication MARC 21 Format for Bibliographic Data and a summarized single volume work entitled MARC 21 Concise Formats. For continued work with MARC records, these sets are highly recommended. They are detailed documents containing many examples. (See the bibliography for complete reference.)
In the MARC record, 10% of the tags are used over and over, and the other 90% are seen only occasionally or rarely. After even a short exposure to the MARC 21 format, it is not unusual to hear librarians speaking in 'MARCese.' Librarians who work with MARC records soon memorize the numbers for the fields common to the materials they catalog.
An outline of those 10% of the tags which are used most frequently is included with this brochure in Part VII. A brief list of some of the other tags is included in Part VIII.
2. Some fields are further defined by INDICATORS.
Indicators: Two character positions follow each tag (with the exception of Fields 001 through 009). One or both of these character positions may be used for indicators. In some fields, only the first or second position is used; in some fields, both are used; and in some fields, like the 020 and 300 fields, neither is used. When an indicator position is not used, that indicator is referred to as 'undefined' and the position is left blank. It is the convention to represent a blank, or undefined, indicator position by the character '#'.
Each indicator value is a number from 0 to 9. (Although the rules say it can be a letter, letters are uncommon.) Even though two indicators together may look like a 2-digit number, they really are two single-digit numbers. The allowable indicator values and their meanings are spelled out in the MARC 21 documentation. In the example which follows, the first 3 digits are the tag (245 defines this as a title field) and the next 2 digits (a 1 and a 4) are indicator values. The 1 is the first indicator; 4 is the second indicator.
A first indicator value of 1 in the title field indicates that there should be a separate title entry in the catalog. In the card catalog environment, this means that a title card should be printed for this item and an entry for 'Title' added to the tracings. A first indicator value of 0 would mean that a title main entry is involved; the card would be printed with the traditional hanging indention, and no additional tracing for the title would be required (since it is the main entry).
Nonfiling characters: One of the more interesting indicators is the second indicator for the title field. It displays the number of characters at the beginning of the field (including spaces) to be disregarded by the computer in the sorting and filing process. For the title The emperor's new clothes, the second indicator is set to '4' so that the first four characters (the 'T,' the 'h,' the 'e,' and the space) will be skipped and the title will be filed under 'emperor's.'
3. SUBFIELDS are marked by SUBFIELD CODES and DELIMITERS.
A subfield: Most fields contain several related pieces of data. Each type of data within the field is called a subfield, and each subfield is preceded by a subfield code. Fields 001 through 009 have no subfields.
For example, the field for a book's physical description (defined by the tag 300) includes a subfield for the extent (number of pages), a subfield for other physical details (illustration information), and a subfield for dimensions (centimeters):
A subfield code: Subfield codes are one lowercase letter (occasionally a number) preceded by a delimiter. A delimiter is a character used to separate subfields. Each subfield code indicates what type of data follows it. (For each field in the MARC 21 bibliographic format, the MARC 21 documentation lists and describes the valid subfield codes.)
A delimiter: Different software programs use different characters to represent the delimiter on the screen or on printouts. Examples are a double dagger (), an 'at sign' (@), a dollar sign ($), an underline ( _ ), or the graphic symbol '. In this publication the dollar sign ($) is used as the delimiter portion of the subfield code.
In the example above, the subfield codes are $a for the extent, $b for other physical details, and $c for dimensions.
4. CONTENT DESIGNATORS is an inclusive term used to refer to tags, indicators, and subfield codes.
The three kinds of content designators -- tags, indicators, and subfield codes -- are the keys to the MARC 21 notation system. In his book, MARC for Library Use (2nd ed. (Boston: G.K. Hall & Co., 1989), p. 5), Walt Crawford calls the MARC system a 'shorthand notation' system. The three types of content designators are the shorthand symbols that label and explain the bibliographic record.
5. Some GENERAL RULES.
There are some general rules that help define what all the numbers used as field tags mean. Please note that in discussions of MARC 21 tags, the notation XX is often used to refer to a group of related tags. For example, 1XX refers to all the tags in the 100s: 100, 110, 130, and so on.
A. Tags divided by hundreds. The basic divisions of the MARC 21 bibliographic record are:
| 0XX | Control information, numbers, codes |
| 1XX | Main entry |
| 2XX | Titles, edition, imprint (in general, the title, statement of responsibility, edition, and publication information ) |
| 3XX | Physical description, etc. |
| 4XX | Series statements (as shown in the book) |
| 5XX | Notes |
| 6XX | Subject added entries |
| 7XX | Added entries other than subject or series |
| 8XX | Series added entries (other authoritative forms) |
The 9XXs have been left for locally-defined uses, such as local barcode numbers. Local libraries, vendors, or systems can define and use them for attaching other types of information to records. (X9Xs in each of these groups -- 09X, 59X, etc. -- are also reserved for local use, except 490.)
The list of the most common tags shows how each fits into one of these divisions: 100 is an author main entry, 520 is a summary note, and so on.
B. Access points: Access points (a main entry, subject added entries, and other added entries) are an important part of the bibliographic record. These are the headings for which separate cards were created for the traditional card catalog, and which a patron or librarian can search in an online catalog. Most of the access points are in:
| 1XX | fields (main entries) |
| 4XX | fields (series statements) |
| 6XX | fields (subject headings) |
| 7XX | fields (added entries other than subject or series) |
| 8XX | fields (series added entries) |
These are the fields that are under authority control.
'Authority control' means following a recognized or established form. Usually, a cataloger chooses subject and name headings from a list of approved headings. In a conversation, if you talked about visiting the 'Getty Museum' and the 'J. Paul Getty Museum' in California, your listener would know you meant the same thing. But if a cataloger sometimes uses 'Getty Museum' and other times uses 'J. Paul Getty Museum' as headings in a catalog, the library user will have a difficult time finding all the books on that subject. If a cataloger follows the Library of Congress's list of established forms for names, he or she will use the heading 'J. Paul Getty Museum.' As long as the cataloger always uses one established form, all the books on that museum will be found in one place in the catalog.
For names, the best authority is the Library of Congress Name Authority file. This file is available in machine-readable format from the Cataloging Distribution Service (CDS) of the Library of Congress or online at http://authorities.loc.gov. The form of the name used (personal name, corporate name, conference or meeting name, series title, or uniform title) can be checked against this authority.
For topics or geographic names, the common subject authority lists are the Library of Congress Subject Headings or the Sears List of Subject Headings. The form of a subject heading should match one on the list or follow the rules for construction.
In a desktop computer system, it is difficult to store all of the Library of Congress authority files. Five gigantic volumes are required to list the Library of Congress Subject Headings. The portion used by a school or special librarian would be only a fraction of the whole.
What is more important on the computer-based library catalog is what is termed 'local authority control.' Local authority control allows the librarian to look at the list of subject headings or the list of author names and ask to reuse one that has already been entered. In that way, all headings for the same person or same subject will be entered exactly the same way -- which is the point of authority control. Names shown in Cataloging in Publication (CIP) data in books are also based on Library of Congress authority records at the time of publication. The forms shown for current publications in an online catalog after a retrospective conversion of data should be correct, since nearly every book or data vendor's database is based on Library of Congress MARC files.
The term 'retrospective conversion' describes a project that converts bibliographic records from their present form -- such as shelflist cards or a brief circulation record -- to full machine-readable bibliographic records. The term retrospective is used because the project is done for a library's existing collection -- everything placed in the library up to the present time. Usually the retrospective conversion is done by 'matching' a library's old records (whether on cards or in a non-MARC format) to a database of full records in machine readable form. Rather than rekeying old records, a librarian can purchase the equivalent MARC records.
C. Parallel content: The fields requiring authority control are also the fields that use parallel tag construction. In general, in the 1XX, 4XX, 6XX, 7XX and 8XX fields, a personal name will have the last two digits 00. Therefore, for a main entry (1XX) that is a personal name (X00), the correct tag is 100. For a subject heading (6XX) that is a personal name, the tag is 600, and so on. This parallel content can be summarized as follows:
| X00 | Personal names |
| X10 | Corporate names |
| X11 | Meeting names |
| X30 | Uniform titles |
| X40 | Bibliographic titles |
| X50 | Topical terms |
| X51 | Geographic names |
By combining this chart with the chart 'Tags divided by hundreds' (above), it becomes evident that if the subject of a book (6XX) is a person (Lincoln, Abraham), the tag will be 600; if the subject of the book is a corporation (Apple Computer, Inc.), the tag will be 610; if the subject of the book is a topic (Railroads), the tag will be 650; if the subject of a book is a place (United States), the tag will be 651. An added entry (7XX) for a joint author (a personal name) will have tag 700.
The Dewey Decimal classification uses a similar construct in its tables for geographic locations or standard subdivisions.
6. Unique information appears at the beginning of the MARC record.
Preceding the main bibliographic record parts -- which are known to all librarians because of their presence on catalog cards -- the MARC record contains some less familiar information. Automated cataloging systems usually provide default data or prompts to help a cataloger input this information.
A. Leader: The leader is the first 24 characters of the record. Each position has an assigned meaning, but much of the information in the leader is for computer use. MARC record creation and editing programs usually provide a window or prompts to assist the cataloger in filling in any leader data elements that require input. The details required for interpreting the leader are in Part IX of this brochure.
B. Directory: MARC records are called 'tagged' records. Before it becomes a tagged record, a MARC record (in what is called the MARC communications format), looks very different -- like one long run-on sentence. In the communications format, the fields are not preceded by tags. However, immediately following the leader is a block of data called a directory. This directory tells what tags are in the record and where they are placed (by a count of the characters to the position where each field begins). The directory is constructed (by computer) from the bibliographic record, based on the cataloging information, and, if any of the cataloging information is altered, can be reconstructed in the same way. Part XI displays a record in MARC 21 communications format, including its directory.
C. The 008 field: The 008 field is referred to as Fixed-Length Data Elements, or Fixed Field Codes. Its 40 characters contain important information, but in an abbreviated form. Although it is not yet used to its fullest in online catalog systems, this field can be used to identify and retrieve records matching specific criteria.
For example, there is a code in this field to indicate whether a book is large-print, a code to identify the country of publication, a code to identify juvenile materials, a code to indicate the language of the text, and so on. The details required for interpreting the 008 field for books are in Part X.
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Part IV:
Where Do MARC Records Originate?
Shared cataloging information -- shared bibliographic records -- has been a reality for a number of years. Many librarians have chosen to maximize limited resources by acquiring cataloging data rather than creating it themselves. For almost a century they have been able to order sets of catalog cards for their new books from the Library of Congress, or, more recently, from book jobbers.
Others typed their own cards, using the Cataloging in Publication (CIP) data found on the verso of the title page of many books. Librarians also adapted the partial or full cataloging records printed in library journals or in bibliographies.
Once computers became available, it was no longer necessary for librarians everywhere to constantly 'reinvent the wheel.' Why should hundreds of catalogers each use valuable time to compose nearly identical cataloging records for the same item when one cataloger could do it and share the record that had been created? Why should hundreds of typists retype that same record on cards when a computer could be programmed to print them?
After the MARC record was developed, libraries shared in the benefits of machine-readable cataloging whether they had an online system or not. The cards, purchased from the Library of Congress or from a jobber, were computer-printed from bibliographic records based on Library of Congress MARC files.
Colleges and universities with large library budgets joined bibliographic utilities such as OCLC, WLN, RLIN, and A-G Canada. For an on-going fee plus communication costs, their technical service departments went online with the utilities' powerful mainframe computers. These ventures allowed those libraries to use and contribute MARC records. Catalog cards could be ordered, and a printer could be hooked up to the system to receive data over the phone lines and print book labels.
Now we are in an exciting age when powerful, inexpensive computers are available for the management of library operations in all types and sizes of libraries. Computer software programs allow an individual library to have its own self-contained circulation system or online public access catalog. These programs often can read, store, and print MARC records. Today's computers use hard disks and floppy disks for storage of information rather than the tape drives used by mainframe computers. For computers, data is commonly sent and received on floppy disks. From the floppy disks, bibliographic records are uploaded to the stationary hard disk.
As library automation technology changes and as cataloging needs change, the MARC 21 formats and related MARC 21 documentation are changing also. Although the MARC format was originally developed by the Library of Congress and the MARC 21 format documentation is maintained and published there, the Library does not make changes or revisions unilaterally.
Two groups which are responsible for reviewing and revising MARC 21 format documentation are MARBI and the MARC Advisory Committee. The Machine-Readable Bibliographic Information (MARBI) Committee is a committee of the American Library Association (ALA) and is composed of three representatives from each of the three function-oriented divisions of ALA: ALCTS (technical services function); LITA (automation); and RUSA (reference). ALA tries to assure that all types of expertise are represented on MARBI. The MARC Advisory Committee is composed of representatives from the national libraries, the bibliographic utilities, vendor groups, and other library and scholarly associations. MARBI meets in conjunction with the MARC Advisory Committee at each ALA conference (annual and mid-winter). The major activity of the Committee is the review of discussion papers and proposals submitted by or through the Library of Congress for changes or additions to existing MARC formats, or the development of new MARC format support in emerging areas.
In 1987, the Library of Congress issued the first edition of the document MARC 21 Specifications for Record Structure, Character Sets, and Exchange Media to aid libraries and other organizations who create or acquire MARC 21 records. Subsequent editions were published in 1990, 1994, and 2000. This document provides technical information on the structure of MARC records, the character sets used in MARC records, and the format for distribution media for MARC 21 records. It is intended for the use of personnel involved in the design and maintenance of systems for the exchange and processing of MARC records.
With the proliferation of computer systems in libraries, it became apparent that a standard was also needed for the exchange of MARC records on floppy diskette. Working closely with representatives from book and data vendors and library automation systems vendors, MARBI and the Advisory Committee recommended proposals which resulted in the necessary changes and additions to the MARC 21 format to fully specify record transfer using diskettes.
More recently, specifications have been developed also for the distribution of MARC records via file transfer (FTP). The diskette and FTP distribution specifications first appeared in the 1994 edition of MARC 21 specifications.
Librarians, vendors -- anyone at all -- who distributes cataloging data should be able to provide standard MARC 21 cataloging in standard format. Library automation systems vendors should be able to design their systems to correctly receive and process standard MARC records. Individual librarians using computers to manage their libraries are the direct beneficiaries of all this MARC 21 standards work.
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Part V:
MARC Data Issues
As computers and technology continue to advance, important issues arise about the quality of library data and computer-based library automation systems. You need to be aware of these issues and their importance to your library.
A. Data questions: When bibliographic records are evaluated, some important questions which need to be addressed are: What is the quality of the MARC data? Which MARC 21 fields are present? Is the data based on Library of Congress MARC records? If so, is the full information that is available on those files evident in the records? Is anything added to the record?
Some librarians ask several vendors of bibliographic data for printed examples of their MARC records in order to compare their fullness and compliance with MARC 21 standards.
Clearly, the contents of the bibliographic records will determine the success of a library's automated operations to a very great extent, for you and your patrons. It is very important to ensure receipt of the highest quality records available.
B. Software questions: The next logical questions to ask are: Does the library automation system being evaluated make full use of the cataloging information? Does it retain all the data and the MARC 21 content designators?
Does the system load in the full record, with no unreasonable or false limitations on such things as the number of subject headings it will index or the length of the note fields? Even though the disk contained excellent, full records, any library automation system will be able to use only what was transferred to the hard disk. (If a circulation system loads in only circulation data, it is important to keep the MARC 21 data disks for upgrading to full bibliographic records at a later time, in order to expand to an online catalog.)
Are the MARC tags, indicators, and subfield codes still present on the librarian's data entry screen? Are the indicators used correctly? Are the subfield codes used correctly? (The information in Part VII will help in evaluating correct use of the content designators.)
After records are added to a database, it is important to store them in the MARC 21 bibliographic format. Future projects may require their use. The MARC format is an industry-wide standard. As additional programs become available, a library's ability to participate in them could hinge on the quality of its bibliographic records.
That brings up one other point. Does the system allow for downloading, or writing the records back out to a disk, to use in other projects such as a union catalog project? Will a program be available to write them in the MARC communications format? (See Part XI for a discussion of various communication and screen formats.)
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Part VI:
In Conclusion
In these pages you've learned what the acronym MARC means. You've seen why a standard format for identifying elements of bibliographic data became necessary and why it is still important. You've learned to d efine and identify the three types of MARC content designators: tags, subfield codes, and indicators. Most important, with this knowledge you can understand the questions that should concern you when considering the purchase of bibliographic data or of a library automation system.
To build on this basic introduction to the topic, additional reading on the subject or courses in online cataloging can be beneficial. Further readings are suggested in the bibliography. MARC may appear difficult at first, but with knowledge and use, it will begin to make sense. As you become more familiar with MARC, the simpler it will become.
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[ Back to Table of Contents ] -- [ Continue to Part 7 ]
Library of Congress
Library of Congress Help Desk ( 10/27/2009 )
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libusb.org, libusbx.org and libusb.info
libusb.org was the original home for libusb project. Now it still exists but the information and code are quite outdated.
libusb.info is the current home page for libusb project.
libusbx was a fork of libusb and libusbx.org is its website. As of 2014.01.26, libusbx project has been fully merged back into libusb and is being discontinued. libusbx.org is no longer related to libusb project.
libusb-win32, libusbK and libusb project
Take note libusb-win32 and libusbK projects are separate projects and both of them use libusb-win32 mailing list for technical support. Unlike libusb which is a cross-platform project, libusb-win32 and libusbK project are both Windows only project.
libusb-win32 project includes libusb0.sys (Windows WDM kernel driver in device driver mode or filter driver mode) and libusb0.dll (libusb-win32 API, library). libusb-win32 API is a superset of the libusb-0.1 API supported by libusb-compat. libusb0.dll supports device using libusb0.sys and libusbK.sys.
libusbK projects includes libusbk.sys (Windows KMDF kernel driver) and libusbK.dll (libusbK API, library). libusbK API is Windows only and libusbk.dll supports device using libusbK.sys, libusb0.sys and WinUSB.
libusb Windows backend can support device using libusbK.sys (and libusb0.sys driver -- not recommended due to issues) through libusbk.dll provided by libusbK project. If libusbk.dll is present, it will use libusbK.dll as the intermediate library to support device using WinUSB driver. If libusbK.dll is not present, then it will directly talk to device using WinUSB using WinUSB API. libusb Windows also supports device using generic HID driver or usbdk driver.
What about usbdk?
usbdk is another open-source generic USB driver. usbdk is a new backend added in libusb-1.0.21 release. The major benefit is that you can keep the existing driver. It supports isochronous transfer as well.
Licensing
What is the libusb license?
libusb is released under version 2.1 of the GNU Lesser General Public License (LGPL).
Dec 12, 2016 How to Show /Library Folder in MacOS Mojave, High Sierra, Sierra. From the Mac OS Finder, go to the Users home folder. Pull down the “View” menu and choose “View Options”. Choose “Show Library Folder” in the settings options for the User home folder. Mac os finder show library folder.
Can I use libusb in a proprietary application?
You can, as long as you don't modify its source code.
If you modify the source, then you must make any changes you applied to libusb public, and grant others the right to use these changes in their own applications, under the LGPL v2.1 license terms.
Getting help
How can I get help? What is the best practice to describe my issues?
Please read the libusb Troubleshooting page and use the mailing list for support.
I tried to post to the libusb mailing list but it failed. Why?
You have to subscribe to the mailing list in order to post.
Running libusb
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Can I run libusb applications on Linux without root privilege?
Yes.
The standard solution is to use udev rules. Here are some links to udev related websites.
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How can I run libusb applications under Mac OS X if there is already a kernel extension installed for the device?
If there is no existing kernel extension installed for the device, libusb will run out of the box, you do not even need to have root privilege and there is no need to set up udev rules like Linux. However, if there is an existing kernel extension installed for the device, then it is more troublesome. There are ways to get libusb working and they all require some interventions as root.
1) You can use kextunload to unload the kernel extension. You need to run the command as root. Take note this may not be possible for drivers like USB HID since it may be used by other USB HID device. Take note that the kextunload command will lose its effect in the next boot.
The above command will unload the Apple provided FTDI driver (Mac OS X Mavericks or later).
The above command will unload the FTDI provided VCP driver.
2) You can use a codeless kext to prevent the kernel driver from attaching to the device. Take note that OS X Mavericks and later require that the kext be signed using a special Developer ID.
Please read the following two Apple technical notes for more details about writing a codeless kext.
3) In certain cases, you can manually edit the Info.plist configuration file of a kernel extension to prevent it from loading for certain VID/PID combination.For example, in the case of Apple provided FTDI driver, you can edit the following file to comment outthe key/dict sections of the desired VID/PID combination.
Once you finish the editing, you can issue the following two commands and everything should work after that.
Reference:
How to use libusb under Windows?
Please refer to the following Wiki page:
https://github.com/libusb/libusb/wiki/Windows#How_to_use_libusb_on_Windows
Basically you will need to install a supported driver.
- If your device is a generic HID device, no extra driver is needed since it is supported. But HIDAPI is recommended for HID device than libusb Windows.
- If your device uses WinUSB driver, no extra driver is needed since it is supported natively.
- If your device uses libusbK driver, you should be set as well (libusbK.dll should have been installed).
- If your device uses libusb-win32 (libusb0.sys) device driver, please switch to libusbK driver.
- If your device uses libusb-win32 filter driver, please uninstall the filter driver and try usbdk instead.
- If your device uses other driver, and you do want to keep using the existing driver, then try usbdk.
- If your device uses other driver and you are okay with switching drivers, then switch to WinUSB (preferred) or libusbK driver.
Can libusb be used on the USB device side, e.g. Linux Gadget Device?
No.
libusb only provides an API for writing software on the host. Of course, if the device also acts as a USB host then libusb could still be useful, but only for the host part of the device.
Can I use libusb to open a file on an USB storage device?
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Yes.
libusb can be used for low-level communication with USB Mass Storage Class devices. But in order to access a file on such a device you must first implement Mass Storage Class, SCSI and the particular file system used on the device, most commonly FAT32.
However, libusb will not do this part for you. In a word, do not use libusb for USB mass storage device.
But you can find a limited example of how to read a data block through Mass Storage using libusb in the mass_storage test from the xusb.c sample of the the libusb distribution.
Does libusb support USB 3.0?
Yes (as long as the underlying OS supports USB 3.0 too).
My device works when plugged on an USB 2.0 port but not on an USB 3.0 one
If you encounter such an issue, you should report it to the libusb mailing-list.
But please note that USB 3.0 is fairly new, so some Operating Systems are still catching up.
For instance, USB 3.0 support for Windows 7 and earlier is very dependent on individual drivers, which are provided by the USB controller manufacturer, and not Microsoft. Some of these have been known to have bugs. Only Windows 8/8.1/10 and later have an official USB 3.0 stack that originates from Microsoft.
For Linux, the xHCI driver may also not be as mature as the other host controller driver. As of now (27-Dec-2016), things should be much better. Please try to upgrade to later version of the kernel whenever possible to have better support.
For Mac OS X, xHCI support has only been introduced recently with Mac OS X Mountain Lion, so USB 3.0 support may not be that mature either. Things should be better now (27-Dec-2016). Whenever possible, please upgrade to later version of Mac OS X for better support.
We will try to help you sort issues related to USB 3.0 usage where possible. But before you contact us, if on Windows 7, please make sure you test with the latest USB 3.0 drivers available from your xHCI provider, or, if on Linux, please make sure you test with the latest kernel, as the xHCI driver is regularly being updated there.
Does libusb support USB HID devices?
If your application will revolve around HID access, you are strongly encouraged to try to use the HIDAPI library by Signal 11 Software, which is also cross-platform. It uses native HID API under Windows and Mac OS X. It use either hidraw or libusb as the backend under Linux.
libusb was widely used to access USB HID device under Linux for historical reasons so there may be use cases to use libusb for HID device due to existing code base or for platforms without HIDAPI support. However, the level of support as well as the ease of access of HID devices, depends on the platform you will be running libusb on.
On Linux, you must detach the kernel HID driver for libusb to communicate with the device, but the libusb API can do this for you. If you have a relevant udev rule, you should also be able to perform that operation without requiring root privileges. Still HIDAPI is recommended for new development.
On Mac OS X, you must install a codeless kext kernel driver and then reboot, before you will be able communicate with the device. This may not be easy with the release of later Mac OS X versions. So it is not recommended. HIDAPI should be the library of choices if you need Mac OS X support.
On Windows, the native Windows HID driver is supported by libusb, but there are some limitations, such as not being able to access HID mice and keyboards since they are system reserved, as well as getting a direct read of HID report descriptors.
Under NetBSD/OpenBSD, you may have to rebuild the kernel in order to use libusb with the HID device. Please refer to the apcupsd page.
In general, you may find HIDAPI a better library for HID device.
Platform Support
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Does libusb support Windows RT?
No.
Windows RT is locked by Microsoft, which means that users cannot install the applications or library of their choice. As such, libusb has no plans to support Windows RT.
Does libusb support Apple iOS device?
No.
Does libusb support Windows CE based device?
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Yes.
Please refer to the Windows CE related information in the following file.
https://github.com/libusb/libusb/blob/master/INSTALL_WIN.txt
Does libusb support Android
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Yes.However, this will only work if your device has USB host support (also known as USB On-The-Go) and if you have sufficient privileges to run in host mode (which usually requires a 'rooted' device).Please check the android directory for more info.