Thursday, November 27, 2008

Introduction to libraries: Types of library catalogues

What is a library catalogue?
A library catalogue lists the materials held by the library. It also indicates where each item is located in the collection. Depending on the library, the description of items may be brief or very detailed. A library may or may not include every item in its catalogue. The library may produce a separate list or bibliographies of pamphlets, clippings or other special materials.

Functions of a library catalogue

All library catalogues, regardless of format, inform the library user:
  1. Whether the library owns a particular copy of a particular item.
  2. Which works by a specific author are in the collection.
  3. Which editions of a particular work the library owns.
  4. What materials are available on a particular subject.
  5. About the following details for each item:
    a. Author
    b. Title
    c. Imprint
    d. Collation (number of pages, whether the item has illustrations, etc.)
    e. Subject headings
    f. Location in the collection

More recently, library catalogues also refer patrons to outside sources, such as sites on the Internet, and allow the patron to link directly to that site from the library’s catalogue.

Types of library catalogues
The four types of library catalogues are listed below.
1. Card catalogue
2. Book catalogue
3. COM catalogue
4. On-line Public Access Catalogue (OPAC)

Access points
Library catalogues provide access to items by their author, title, subject, co-author, translator, illustrator, and by series title. Each author’s name, or title, etc. is often referred to as an access point or entry. The catalogue will also provide the call number for each item, so that it may be located on the shelf.

Card catalogue format
All catalogues contain bibliographic records, but may represent this information differently.

OPAC format
To see the bibliographic record of Introduction to library public services displayed in Red River College (RRC)’s Library’s on-line catalogue, go to RRC’s Library Website: Click on “Search for books, etc.” on the right-hand side of the page. The “Simple Search” screen will appear with a “Search for” box. Enter the title of the book, Introduction to library public services. Then in the “Search by” menu, select “Title keyword” and then click on “Search”. The search will generate only two titles, select the first one, which is the 1992 edition. Note that each part of the record is labelled, making it easy for the library client to understand what information is being provided. Notice how certain items are underlined. If you were to point your mouse and click on Evans, G. Edward, the catalogue would automatically display a listing of all the works the library has by authors with the surname Evans. This list of course includes all titles by G. Edward Evans that the library has in the collection. Similarly, if you were to point and click on the subject heading “Reference services (Libraries)”, the catalogue would display a list of all the items available in the library on that subject.
The wide variety of on-line catalogues available on the Internet can be explored through Libdex: The Library Index (formerly, webCATS: Library Catalogues on the World Wide Web), created by Peter Scott and Doug Macdonald of the University of Saskatchewan Libraries. Its Web site address is

Advantages and Disadvantages
Each of the four major types of catalogues has its advantages and disadvantages.

Card Catalogues
Until the early 1990s, this was the most familiar type of catalogue. The card catalogue is made up of 7.5 cm x 12.5 cm cards, each containing a full bibliographic record or part of a bibliographic record. These cards have a small hole in the middle of the card near the bottom edge. The cards are filed alphabetically by the entry in metal or wooden drawers in cabinets.
Each drawer has a rod extending the full length of the drawer. The rod is fed through the hole at the bottom of each card to keep them secure whenever a drawer is removed for consultation. The rod also serves the purpose of allowing filing to be double-checked for accuracy. When cards are first filed, they are placed above the rods. Another library staff member will then double-checked the filing. When all cards are filed correctly, the rod is removed to allow the new cards to fall into place and then returned to the drawer to secure the cards once more.
Card catalogues are often divided catalogues. This usually means that the catalogue is divided into two (or three) alphabetical sequences, one for authors and titles (or titles may have its own alphabetical sequence in a three-way divided catalogue) and one for subject headings. If a card catalogue is a dictionary catalogue, it is one alphabetical sequence with all entries inter-filed. Most libraries prefer divided catalogues.
The fronts of the cabinet drawers have labels to indicate which alphabetical sequence is contained in each drawer, assisting the library user in quickly identifying the drawer they need to consult. In a divided catalogue, the labels may be colour-coded to identify whether a drawer belongs to the author/title or subject alphabetical sequence.
Although most libraries have now abandoned the card catalogue, we must not lose sight of the fact that it was a truly ingenious invention, serving the needs of library patrons admirably for many years. Unfortunately its disadvantages now outweigh its advantages in an electronic age.

Card catalogue advantages
1. Flexibility and currency: Staff time and size of collection growth permitting, cards for new materials can be added quickly and cards easily removed for those items no longer in the collection. The card catalogue is as up-to-date as your cataloguing and filing.
2. Ease of use: Library clients are comfortable with the alphabetical approach and can easily adapt to a divided catalogue. It is not much different from using either the white or yellow pages of a phone book. The white pages are for specific names of people and businesses (author/title drawers) and the yellow pages are for listings of companies in a particular type of business or people in a specific profession (subject drawers).
3. Availability: The likelihood of more than one person needing the same catalogue drawer at the same time is minimal. Unless, of course, every student in a class has been given exactly the same topic to research. This is often referred to as a queuing problem (i.e. everyone must wait in line).
4. Costs: In smaller libraries, the cost of maintaining a card catalogue is not overly expensive. Card stock is readily available and there are software programs that can produce catalogue cards on a computer printer. Libraries can now order prepared catalogue cards from their book supplier, which may only require the call number to be added.

Card catalogue disadvantages
1. Size: As the collection grows, so does the card catalogue. This takes up precious space which could be used to house more materials.
2. Human error: Even the most careful filer can make mistakes and these mistakes can be overlooked by someone checking for accuracy. A single card misfiled can lead to another card being misfiled. When large academic libraries had card catalogues, double-runs as they were fondly called, could become extremely large, resulting in hours of re-filing cards in their proper order. When a horrified gasp from a co-worker was heard as they were filing or checking it was known exactly what they had discovered.
3. Ease of use: Because of the way cards are filed, only one bibliographic item can be viewed at a time. Only the first word of a title or subject heading is accessible. If a patron cannot remember the first word of a title or does not know the exact subject heading, he or she may not find the item.
4. Costs: It takes time to file and pull cards and staff time is costly. When libraries have branches, it can be expensive to maintain many catalogues in many locations.
5. Flexibility and currency: Individual cards are not easily altered and may have to be reprinted. Before computer production of cards, many libraries purchased electric erasers to remove outdated headings on cards. Electric erasers were delicate instruments to use. If a person pressed too hard, the eraser would eat right through the card stock.

Book catalogues
A book catalogue lists bibliographic records in alphabetical order by various entries, or by classification number. There may be more than one record on each page. The pages are then bound into a cover, forming a book. Canadiana, a list of materials of Canadian origin or interest catalogued by the National Library, is an example of a book catalogue.

Book catalogue advantages
1. Ease of use: A book catalogue is like using a dictionary and requires little instruction in use. A whole page of entries can be scanned at once.
2. Size: It is compact in size, allowing it to be carried anywhere within the library.
3. Costs: The first copy is the most expensive to produce. If the book catalogue is not too large, many copies can be made and distributed throughout the library, to classrooms, offices or other branch libraries.

Book catalogue disadvantages
1. Ease of use: Unless multiple copies are made, there is a queuing problem. Only one person can use the catalogue at a time.
2. Flexibility and currency: Bibliographic records for new materials cannot be inserted. A whole new book catalogue must be produced or a supplement created. Supplements require the library patron to search in at least two alphabetic sequences for each item.

Microform catalogues
There are two types of microform catalogues. Some libraries have photographed each catalogue card in alphabetical sequence then transferred these images onto microform or microfiche. When bibliographic records were first available in electronic format, high-speed cameras would photograph screen images and these images would be transferred onto microform. These are known as COM or computer output microform catalogues.Microform catalogues have been quickly overtaken by on-line catalogues are now primarily used as a backup when an on-line system goes down.

Microform catalogue advantages
1. Ease of use: Like the book catalogue, many records can be scanned at one time. Indexes can provide easy access to a specific alphabetic sequence. Headings at the top of the fiche indicate the first entry on each fiche and each fiche is numbered sequentially for easy filing.
2. Size: Microfiche or microfilm takes up very little storage space and can store many records on one fiche or film.
3. Costs: Multiple copies are very inexpensive to produce.

Microform catalogue disadvantages
1. Ease of use: Microform is an extremely unpopular format. Equipment is required to use the catalogue. Fiche can be easily misfiled or placed one behind another in the holders. Library users are frustrated when the fiche they require is missing. Many copies of the catalogue and machines are required to avoid problems with queuing.
2. Flexibility and currency: New bibliographic records can not be inserted, nor can records for lost items be deleted. Like the book catalogue, the entire catalogue must be reproduced to incorporate changes. Most libraries choose to produce supplements.
3. Costs: The first copy of the microform catalogue is very expensive to produce. There are also maintenance costs involved with the equipment.

Integrated library systems
It is important to understand that an OPAC is merely a single module within an integrated library system. The major functions within a library are:

  • Acquisitions
  • Cataloguing
  • Circulation
  • Serials
  • Reference (online public access catalogue, access to electronic reference resources)

Integrated library systems definitions
An integrated library system automates library functions. Beverly Duval states that “An integrated library system is one whose functions use a single database made up of a collection of files. All the functions are fully interactive with one another and are kept automatically in synchronization. For example, if a book is checked out at circulation, that is simultaneously reflected in the OPAC”. (Duval, Beverly and Main, Linda. Automated library systems: a librarian’s guide and teaching manual. Westport, Conn.: Meckler, 1992. p.5)

An integrated library system can talk or interface with external sources on the Internet such as vendors for library materials and cataloguing utilities where cataloguing records can be imported into the local library’s catalogue.You may also hear the term turnkey system. Duval defines this term as, “an automated library system which has been designed, programmed and tested by a vendor and then offered for sale to libraries, ready to be installed and operated. In theory, when the system is delivered and installed, all that is required is to plug it in and turn it on”. (Ibid, p. 258)

Most libraries do not develop their own systems, as there is a wide variety of systems on the market. However, note carefully Duval’s wording, “in theory”. It is not always that easy to install a new automated system and have it running smoothly right away. Library staff find that when they change another system (called “migrating” in the library world), all sorts of unforeseen issues arise. Many of them stem from inconsistent or unsophisticated use of MARC coding. Because turnkey systems often developed for a ‘standard library’, you may find that you will have to make compromises in your choice of system. Often features or complete modules may be missing or still in development. Until very recently, many integrated library systems targeted to school libraries did not have either acquisitions or serials modules.

Databases or files
An integrated library system has several databases or files. The bibliographic database contains a cataloguing record for each distinct item catalogued. The authority files show which headings for persons, corporate bodies, series or subjects have been used and cross-references those names or headings which have not been used. The item files contain records for each physical item. For example, there may be more than one copy of any Harry Potter title given its popularity. There would only be one bibliographic record for the title and two item records, one for each copy, giving the barcode and loan status for each copy. The funds database manages the financial records for purchasing materials. The vendor database contains the names and addresses for all the different publishers, bookstores, or jobbers used to purchase materials for a library. The patron database contains all the information pertaining to each registered patron.

How do these databases and modules relate to one another? The OPAC draws upon almost all the databases, as it will not only list which items are in the library, it will also let the patron know whether the item is on the shelf, signed out and when it is due, missing or lost. The circulation module uses both the patron database and the bibliographic database to link a particular patron to the record for each item he/she signs out. The cataloguing module makes use of the bibliographic database. You may be adding new records, deleting records or modifying existing records. It also uses the authority database to let you know that the author’s authorized heading is already in the catalogue, or that the author writes under more than one name. The cataloguing module interacts with the acquisitions module. As items are ordered, as much bibliographic information is entered so that it may be transferred into the cataloguing module when it is received. The acquisitions module makes use of the bibliographic, funds and vendor databases. The serials module makes use of the bibliographic and funds databases as well as holding information. As each new issue of a magazine is received, it is entered into the serials module. The computer is programmed to know when the next issue is expected and will alert library staff if an issue is overdue.

Before automating
The very first question to be asked before choosing a system is, “How can we improve services to our clients with a new automated system?” If you are automating for the first time, the following steps should be taken:
- Determine improvements in services required or desired
- Evaluate present procedures
- Determine set of tasks, how much time, how much staff
- Determine what type of control needed
- Determine how tasks interrelate

What to look for in an integrated library system
Ease of use:
Are the screens easy to read and understand? Is there online help? Are keystrokes or commands kept to a minimum?
Integration: Can modules be purchased individually or in phases to keep costs down? Do modules truly interact with one another?
Industry standards: Are cataloguing records in full MARC 21 format? Is there authority control? Is the system Z39.50 compatible? Is it a Windows-based system? Can the catalogue be accessed through the World Wide Web? Does the acquisitions module accept electronic data interchange (EDI) documents?
Speed of transactions: If a circulation transaction takes longer than 2-5 seconds, it is too slow. Record input should take only 10 seconds.
Customer support: Is toll-free telephone support provided? Are product guarantees given? Is there a surcharge for maintenance and support? How knowledgeable are the staff providing the customer support?
Training: Does the vendor require staff to attend training sessions? If so, how much time and how much does it cost?
Documentation: Are there manuals? Are they written in “computerese” or English?
Price: Is it within your budget range? Are you getting your money’s worth?Upgrade policy: What are the vendor’s plans for future development?
Multi-user capacity: How is the system networked? Is it reliable when many people are using the system at one time?
Portability: Can bibliographic records be exported should you wish to migrate to another system? Remember that many libraries change automated systems every three to five years if their vendor does not have an aggressive update policy.

Sources of information
There is a lot of information to be gathered before making an informed choice about selecting an integrated automated library system. Fortunately, there are many resources available, including promotional materials from the vendor, books, articles, reviews, exhibits at conferences and visits to other libraries.

Vendors provide a wide variety of brochures, demonstration packages, and testimonials. Most now have Websites which provide a great deal of information about their product.

The following books are helpful in learning about integrated library systems.
Breeding, Marshall. PC-based integrated library systems. Westport, Conn.: Meckler, 1994.
Day, Theresa Thurman, Flanders, Bruce L. and Zuck, Gregory James. Automation for school libraries. Chicago: ALA, 1994.
Meghabghab, Dania Bilal. Automating media centers and small libraries: a microcomputer-based approach. Englewood, Colo.: Libraries Unlimited, 1997.

Journals with reviews
Computers in libraries
Information technology and libraries
Library hi-tech
Library software review
Library technology reports
Library journal
(the first issue in April has a review of various vendors) Integrated library system reports

Recent articles
To obtain recent articles on integrated library systems, consult the following Websites:
ntegrated library system reports
Library automation resources: tools to help you choose a library management system

Sample timeline of an automation project
Compiled from the following article: Adams, Helen. Media magic: automating a K-12 library program in a rural district. Emergency librarian. 21 (May-June 1994): 24-29.

This article describes a project in rural central Wisconsin, in the Rosholt School District. There are two library resource centres, one for K-8, another for 9-12. The system has 650 students altogether.

1986 Committee set up to revise district Media Services Plan
1987 Long range plan presented to Education Board in January
1987 Plan adopted, collections weeded and retrospective conversion begun1987 Nine months spent to complete conversion of 11,000 unique items
1987/88 Vendor research begun
1988 Networked circulation system installed in August
1988 Barcoding in August and September (24 student, community, faculty and administrative volunteers assist)
1990 Networked union catalogue component added (one week to install network, library automation software, build indexes, do backups, run diagnostics, train staff)
1990 Teachers trained at all day open-house, three weeks for student training
1992 New Technology Committee set up to develop comprehensive technology plan (four months taken to produce plan)
1992/93 Implementation of plan (results have included enlarging and enhancing resource centres with the addition of computer labs)
1993 Evaluation of plan submitted to Board in April
1993 CD-ROM resources networked
1994 Modem access to public library catalogue provided in January
1994 Internet access given by University in the fall

Vendors activity
Visit the Library Technology Guides vendor Website at: Search for the following popular vendors by entering their names in the second box: CASPR, Follett Software, Hardcover Software, Kelowna Software, The Library Corporation, SIRS Mandarin Inc. and Winnebago Software. In each case, click on the link to their respective Websites to help answer the following questions:
1. Which modules does this system have: acquisitions, cataloguing, circulation, OPAC, serials, and/or A/V bookings?
2. Does this company seem to be marketing their system to a specific type(s) of library(-ies)?
3. Does this system accept MARC (machine-readable cataloguing)?
4. Does the company provide customer support? If yes, does this include a toll-free helpline?
5. Does the company provide training?
6. Can you place your catalogue on the Web with this system?
7. Does this system support Z39.50 protocol?
8. Is a demo of the system available?
9. Does the vendor provide references of other libraries already using its system?

On-line public access catalogues
As computer technology advances and the price of computer hardware and software decreases, more libraries are converting their catalogues to On-line Public Access Catalogues (OPACs).
Note that many libraries, including those in Third World countries, are providing access to their collections with extremely sophisticated systems using the latest graphical user interface (GUI) technology. Library clients are becoming increasingly comfortable with using computers to search for information and have very high expectations of computers’ abilities.

Looking at bibliographic records in electronic format
In an on-line catalogue, bibliographic records are stored in an electronic database. Each element of a bibliographic record is entered into a separate field. Red River College’s library catalogue can be accessed at and then click on the Search for Books, etc. link.
Search for RRC’s bibliographic record of Carol Shield’s Stone diaries. Carol Shields’ name is the main author field. Stone diaries is in the title field. Each record has a unique record number. This record’s number is 34661, only visible in the “Staff View” screen as MARC (Machine-Readable Cataloguing) field 001. View this MARC record by clicking on the “Staff View (MARC)” button, which appears on the display screen. When a person at the OPAC keys in a request for the author Carol Shields, the computer does not search through every single record for her name. It searches an author index instead. When it finds an index entry for Carol Shields, there will be a list of record numbers for items with her name in the author field. The computer would then respond to the person at the terminal by either listing the actual bibliographic records found (usually in an abbreviated format) or with the number of items found and ask the person if they wish to have them displayed. Searching indexes rather than each entire record enables the computer to respond quickly to a request. Early on-line catalogues were cumbersome to use, requiring users to learn special commands for finding an author or subject heading (e.g. A= or AU= or browse au). GUI-based on-line catalogues now have easy to understand icons. Using a mouse, a user merely has to move a pointer to the icon desired and click for a search by author, title or subject. Searches can now be performed specifying date ranges, media format, publication language, or ISBN number. The combinations seem endless.
Do a keyword search for the RRC Library record for Introduction to library public services (5th edition, 1992) by using only this part of the title, “library public services”. By searching this way, find that this particular record comes up within the top 10 of over 5000 records. Remember how a disadvantage of the card catalogue was that the patron had to know the first word of the title? In this search the word introduction was not entered at all. The computer was able to search several indexes for the occurrence of any of the three words, library, public, or services and rank the records, which contained all three words with the highest relevance.
Search for The stone diaries by entering the author’s name “Carol Shields” as keywords. As a keyword search, it is not important that the author is entered as “Carol Shields” rather than “Shields, Carol”. The computer looked for either of those words in various indexes and ranked those records, which had both, with the highest relevance.
Search for The Time manager by limiting to a particular format. Before searching the keywords, “time management”, set the limit to videorecording. Therefore, when the computer searches for “time management” it only retrieves records for videorecordings containing those two words.That is not to say that on-line catalogues are easy to create and maintain.
Search again for the MARC record of The Stone diaries. Note how it has a much more complex look than the non-MARC display. It is no wonder that in RRC’s OPAC, MARC records are only accessible through the “Staff View”. Even though some systems have created user-friendly screens for entering cataloguing data, a sound knowledge of basic MARC coding is required to effectively catalogue library materials in an on-line catalogue.

On-line public access catalogue advantages
Like any other type of catalogue OPACs have their advantages and disadvantages.
1. Flexibility and currency: OPACs are easily updated. As soon as items are entered, they can be indexed to become accessible. Some systems index new items the moment they are entered. Records are also easily removed from the database.
2. Ease of use: New GUI technology makes OPACs very user-friendly. OPACs offer sophisticated methods of searching for materials. Users can combine terms such as “Shields” in the author field and “diaries” in the title field, limit searches to a particular date range or format. If the OPAC is networked, terminals can be installed throughout the school, university, public library or branches of a library, making catalogues accessible from individual’s desktops. Regional library systems can now access each other’s catalogues. Some libraries offer access to their catalogues over phone lines or the Internet. Clients can search the catalogue from the comfort of their own home.
3. Size: Terminals can take up much less space than bulky card catalogues. Patrons do not have to be physically in the building to access the library’s catalogue.

On-line public access catalogue disadvantages
1. Ease of use: Not all OPAC user interfaces are created equal. Some are menu-driven, intuitive and easy to use. Others may not be user-friendly at all. It would then require staff time to train library patrons. Several terminals would be necessary to avoid line ups. Some form of backup is needed if the system goes down, or the library catalogue will be unavailable. Complicated search strategy options can lead to too many or too few results. This can easily waste users’ time.
2. Costs: Depending on the size of the library, the type of computer hardware, software and networking cable required plus the retrospective conversion of existing bibliographic records in the library’s manual catalogue, the cost can be extremely high. In addition, existing libraries would need to undergo a ruthless weeding of their collection before the retrospective conversion can begin. However, small libraries can now afford microcomputers, which have high capacity memories, making on-line catalogues within their financial reach.
3. Design: If the system is poorly designed, it may require undue switching back and forth between screens to see detailed records. This can be tedious and frustrating for the user.

Classification schemes and call numbers
In ancient times, libraries arranged clay tablets by subject. Classification schemes allow libraries to shelve like materials together. This process is called collocation. Libraries add author numbers, book numbers or cutter numbers to classification numbers to provide a unique call number, identifying where each item is shelved. This way the patron knows the location of the item.
To better understand the concept of collocation, think for a moment how library users might wish to find information about dogs. One person may want material on dogs in general. Another individual might be interested in a specific breed of dogs, such as the basset hound. A well-designed classification scheme would arrange materials about dogs on the shelves in a logical and orderly manner. All books about dogs would be in the same major class and subdivision. The subdivision would have further divisions. Books about dogs could be shelved in the following order:

  1. Books about dogs in general
  2. Books about training dogs
  3. Books about specific breeds of dogs:
    a. Books about Alaskan malamutes
    b. Books about basset hounds
    c. Books about beagles
    d. Books about huskies
    e. Books about Labrador retrievers, etc.

Classification schemes break down the total body of human knowledge into major categories or classes. Within each class, there may be smaller categories, or subdivisions. Classes and subdivisions are assigned either numbers or letters to identify them. This way, all materials on a particular subject will have the same number or letter. Most schemes have the same major classes of knowledge, such as history, science, literature and music.
There are two major classification schemes used in libraries, the Dewey Decimal Classification System (DDC or Dewey) and the Library of Congress Classification System (LC). As a rule, public and school libraries use Dewey and academic and research libraries use LC. The Dewey Decimal Classification System uses numbers for classes and subdivisions. The Library of Congress Classification System uses a combination of letters and numbers.

Dewey Decimal Classification System
The U.S. librarian, educator and social reformer, Melvil Dewey (1851-1931) divided the entire body of human knowledge into ten categories using Arabic numbers to represent each class. Major classes were further divided into ten subcategories and subdivisions were further divided by using decimal places. Consequently, his system is called a decimal classification system and was originally published in 1876. As knowledge continues to grow and expand, Dewey Decimal Classification (DDC) continues to grow and expand along with it. For more information about Dewey, the system and its creator, visit:
Major classes have numerals such as 100, 200, 300, etc. up to 900. The class represented by 600 is technology or applied sciences. History is represented by 900. North American history is assigned 970. Access the Dewey Decimal Classification System Website at:

Dewey Decimal Classification System Examples
If a library has many books on a broad topic, DDC allows each aspect of that topic to be represented by a specific number by adding a decimal point and more numerals.

Example: A book on electronic engineering: 621.38
A book on cellular telephones: 621.38456

DDC numbers are arranged in decimal order on the shelves (e.g. a book with 621.382 is shelved before one with 621.39).
If a library has more than one book on the same topic, an author number or Cutter number or book number is added. These can be the first three letters of an author’s surname, or a combination of one letter and three numbers rep resenting a specific surname as assigned by the Cutter-Sanborn Three Figure Author Table.

Example: 512 Dickensen, D. Introduction to algebra D557i
512 Dickensen, D. Principles of algebra D557p

If the library has several different sections where items may be found, a location code can be added to guide the library client to the correct location of a book. The most common examples of different areas in a library are the reference section and children’s collection.
If the work on electronic engineering was a major handbook and needed to be in the reference section, the call number would read:
R Ref
621.3 or 621.38

Standard location abbreviations are:
R or Ref = Reference, J = Juvenile, LP = Large print, AV = Audio visual

Library of Congress classification system
Instead of numerals, the Library of Congress (LC) uses upper case letters to represent major classes of knowledge. For example, the field of Geography is assigned the letter G. Subclasses are assigned two upper class letters. The subclass GB represents the field of physical geography. Subdivisions of major classes are assigned Arabic numerals. A very specific subdivision may also have a decimal extension.
Explore the Library of Congress Classification outline at:

Library of Congress classification system examples
A Canadian cookbook by Pat Routledge published in 1990, would have the following call number:
TX Class for “home economics”
715.6 Subdivision for “cookbooks…” and a .6 decimal for “Canadian”
.R68 Book number for “Routledge”


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