Memorising the Dewey Decimal Classification (DDC) system 🔢
Memorising the Library of Congress (LoC) classification system 🔠
Other library classification systems 🗃️ (UNDERWAY)
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The DDC for this blog page on classification systems is 025.43
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“How do libraries manage to keep the thousands or even tens of thousands of books on their shelves in an orderly manner, instead of becoming chaotic piles of paper?”
“How is it that a particular book among hundreds of similar titles can be be easily found by staff and patrons ?”
“How can I learn to navigate the shelves without needing to repeatedly refer to a chart?”
“Why are these so many numbers and letters on the book labels??? 😵💫”
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Whoa there, let’s take it one step at a time.
Classification is the act of assigning stuff into groups or categories (compartments within a broader system of organisation) based on their characteristics. It can be thought of as a way of imposing order onto chaos, or as a way of processing information by transforming unstructured data into structured data (other sources about data structuring and info processing: https://www.britannica.com/technology/structured-data, https://www.britannica.com/search?query=information processing, [https://www.britannica.com/technology/information-processing,](https://www.britannica.com/technology/information-processing) https://www.britannica.com/technology/information-processing/Information-searching-and-retrieval, https://www.britannica.com/technology/information-processing/Acquisition-and-recording-of-information-in-digital-form)
For instance, scientists, those in the profession of creating data from observations, experiments, and analyses make extensive use of classification to understand nature and translate its endless complexity into ways that are easier to comprehend..
All of these help scientists organise the myriad of stuff in the world into ideas that have predictable relationships.
Classification is also used in many everyday scenarios too where some level of organisation and assortment is beneficial, such as products in a store’s floorspace or catalogue, income brackets for taxation, visa statuses, triaging hospital patients, military unit types, the grammar of language, district zoning, etc.
Libraries use classification systems so that the resources stocked on their shelves can be organised in a predicable manner. This allows staff members to shelve books in in a consistent way within the library floorspace (e.g., books labelled with 541 on their spine are always placed in the shelf region for the 540s, or at least the 500s), which means any book can easily be found and retrieved by other staff members or by patrons.
Since books are essentially a format of media that exists to convey knowledge and ideas, they are typically classified and organised by those ideas, which are known as ‘subjects’ in the lingo of libraries and scholarship. Books on the subjects of natural sciences, such as astronomy or botany or zoology, would be shelved close to one another since they are based around similar ideas and away from the books on entirely different topics like carpentry, numismatics, painting, Buddhism, or classical Greek literature.
A patron visiting a library would typically be looking for a book on a particular topic to satisfy their information needs, and they would be able to find said book because of a classification and organisation method based on topics/subjects/ideas.
However, what would happen if books were not classified and organised by subjects, but by some other characteristic such as the colour of their covers or their physical size?
Curious George (a cartoon monkey) certainly found out when he was temporarily in charge of the children’s section of a library. Click the image below to watch the full episode on Youtube!
[from ‘George Volunteers at the Library’, hosted on the Curious George Official YouTube channel, viewable on https://www.youtube.com/watch?v=ND2-7m5QFO4]
Some British comedians even made a skit about the problems of organising books by ways other than subject.
[from ‘The Confusing Library’, performed by ‘The Two Ronnies’ viewable with captions on the Flipped ‘and Marked’ youtube channel https://www.youtube.com/watch?v=8dZznfGPYRY]
Furthermore, by ensuring that classification systems are consistent or harmonious between libraries in different regions, it is possible to ensure that any resources loaned from other libraries (Interlibrary Loaning) are also easily located.
The dominant classification systems used in English-speaking countries are the Dewey Decimal System (abbreviated as DDC for Dewey Decimal Classes/Classification) and the Library of Congress system (LoC). One of my assessments for the Cert IV Library course involved making a volunteer training presentation about cataloguing, and one of the slides within that presentation discussed the DDC and LoC systems, so I’ll include it below.
Wikipedia also has a superb page where the DDC and LoC systems are compared to show which numbers categories of the former correspond to the letters categories of the latter. Another webpage that compares the DDC and LoC systems is https://www.librarianshipstudies.com/2026/01/comparison-between-dewey-decimal.html
Note: To see more textual info (text is searchable on this blog, whereas images are not) about each classification system, click the little triangles beside the respective heading.
Other countries may use different classification systems which place an emphasis on their own respective realms of knowledge. Japan, for example, uses the Nippon Decimal Classification System, in which Japanese literature and history are placed earlier in their respective decimal sequences than they would be in the Dewey Decimal Classes (the DDC is noticeably America- and Euro-centric). China has the Chinese Library Classification (CLC) scheme which has a similar letter-based structure to the LoC system.
Law libraries make use of the Moys Classification scheme, which builds on part of the LoC system.
Memorizing library classification systems in-depth may not be required by staff since shelving books is just a matter of placing them in correct numerical and alphabetical order and cataloguing is supported by technical manuals which can be referred to when assigning call numbers.