Libraries and information systems face a fundamental challenge: knowledge never stops growing. Every year, new fields emerge, disciplines evolve, and subjects that didn’t exist yesterday suddenly demand classification. For a library classification system, this constant expansion can be both a blessing and a curse. A system rigid enough to maintain order might become so inflexible that it cannot accommodate emerging knowledge. This is where the concept of hospitality in arrays becomes critical-it’s the ability of a classification system to welcome new subjects without collapsing under its own organizational structure.
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What is hospitality in arrays?
In the context of library classification, hospitality refers to a notation’s capacity to accommodate new concepts or subjects as necessary in the schedules. More specifically, hospitality in arrays means that new subjects can be added without disturbing the existing structure. An array, in classification terminology, is a sequence of classes that share equal rank and are derived using a single characteristic of division.
Think of an array as a shelf of related items. If you have books on different types of animals-birds, mammals, reptiles-they form an array. Now, if a new category like “amphibians” needs to be added, a classification system with good hospitality should allow this insertion without requiring you to rearrange everything that came before or after. Without this flexibility, every time knowledge expands, you’d face the nightmare of reclassification: moving entire collections around, updating call numbers, and disrupting library operations.
Flexibility, often referred to as hospitality in classification, means that the system should accommodate new subjects without disturbing the existing structure. This principle is not merely a convenience-it’s fundamental to the longevity and practical viability of any classification system in an era where knowledge expands rapidly.
Methods for accommodating new subjects
The role of classifiers
In everyday library practice, individual classifiers-librarians responsible for assigning call numbers-use several practical devices to accommodate new subjects. Ranganathan invented the use of sector notation, empty and emptying digits to interpolate and extrapolate new subjects in an array. These devices work at the ground level, allowing classifiers flexibility in their daily work.
One widely used method is the gap device. In this approach, classification system designers deliberately leave vacant numbers throughout the schedules, creating spaces for future subjects. For example, at the level of main class letters, some letters like I, O, X, and Y have not been assigned to any subjects and are available for later use, and gaps have been left between two-letter combinations which can be used for future expansion. However, while practical, the gap device is not always considered scientifically rigorous, as gaps may be arbitrarily distributed and sometimes prove insufficient.
Classifiers also employ several specialized devices for hospitality. The geographical device allows new geographical divisions to be added when needed. The chronological device accommodates temporal divisions-useful when historical periods or eras require new classifications. The subject device allows for new subject-specific divisions based on emerging areas of knowledge. These methods provide classifiers with practical tools to handle subjects that didn’t exist when the classification system was designed.
More the number of devices for hospitality or specificity of subjects, more complex a notation becomes. This presents a real tension: greater flexibility and hospitality often come at the cost of notational simplicity. A system with elaborate accommodation devices might require longer, more complex class numbers, which can confuse users and complicate shelving.
Faceted classification and systematic flexibility
Beyond ad-hoc devices, some classification systems achieve hospitality through their fundamental design. Faceted classification systems provide flexibility and hospitality as new subjects and emerging concepts can be easily accommodated without disrupting the existing structure. This approach, pioneered by S. R. Ranganathan, represents a more systematic solution to the hospitality problem.
The faceted approach provides a more flexible way to incorporate new subjects and disciplines into the classification scheme since the subjects are not included in “a priori categories”. Rather than predetermining all possible classes (as in enumerative systems), faceted systems break subjects into independent dimensions or facets that can be freely combined. Ranganathan identified five fundamental categories known as PMEST: Personality, Matter, Energy, Space, and Time, which provided a universal framework for subject analysis across all disciplines.
For example, a book about medieval Indian philosophy could be analyzed as: Personality (Philosophy), Matter (Indian), Energy (Thought systems), Space (India), Time (Medieval period). If a new hybrid discipline emerges tomorrow, the system can accommodate it by recombining these facets in new ways, without requiring the entire system to be restructured. Unlike traditional systems that often require modifications and expansions to accommodate new subjects, leading to reclassification issues and system rigidity, Colon Classification is inherently expandable, as new subjects can be classified dynamically by synthesizing facets without restructuring the entire system.
The role of classification designers
While classifiers handle hospitality in their daily work, the deeper responsibility for ensuring future-proof systems falls to classification designers-the librarians and theorists who build these systems. These are the experts who must anticipate future needs and build flexibility into the fundamental architecture.
Designers must make critical decisions about notation systems. Every system designer is aware of making provisions to properly accommodate new subjects in later editions without disturbing the existing ones; therefore, in every system some conceptual, structural and mechanical provisions are made to accommodate new subjects at proper places. These decisions have long-term implications.
Classification designers must also decide between enumerative and faceted approaches. Faceted systems are highly flexible and can be easily adapted to accommodate new subjects or interdisciplinary fields, offering multiple classification criteria rather than assigning a single rigid category. This represents a fundamental philosophical choice about how to structure knowledge organization.
Periodic revisions also fall under the purview of designers. New editions of classification systems-such as updated versions of the Dewey Decimal Classification or the Library of Congress Classification-represent opportunities to reorganize arrays, add new subject areas, and improve notational efficiency. However, these revisions must be carefully planned to minimize disruption to existing systems in use across libraries.
Challenges and innovations in classification hospitality
Despite the importance of hospitality, challenges persist. Most meaningful works contain multiple subjects that intersect and overlap in ways that linear classification systems struggle to represent, as modern scholarship increasingly crosses traditional disciplinary boundaries. A single book might combine computer science, philosophy, and ethics-creating challenges even for flexible systems.
There’s also a fundamental tension in classification design: Gap device though popular is not a scientific solution to the problem. Gaps can be filled too quickly, or they might be placed in illogical locations. Some systems run out of space despite careful planning. The Dewey Decimal Classification, for instance, has been criticized for limited hospitality in newer fields. While the Library of Congress Classification was able to incorporate changes and additions of new branches of knowledge, particularly in fields of engineering and computer science due to greater hospitality, DDC has been criticized for being inadequate for covering those areas.
Modern innovations are addressing these challenges. Digital and online classification systems offer new possibilities. All classification systems are now developed in machine-readable databases, offering advantages such as easier searching and browsing of classification notation. This technological shift allows for dynamic updates, faceted searching, and real-time reorganization without the physical constraints of printed schedules.
Additionally, Ranganathan’s ideas continue to influence modern classification systems, digital libraries, and faceted search in databases and metadata indexing. Contemporary information retrieval systems often employ faceted search interfaces inspired by Ranganathan’s principles, allowing users to navigate complex information spaces dynamically.
Conclusion: The ongoing quest for flexibility
Hospitality in arrays represents more than just a technical feature of classification systems-it’s a response to the fundamental reality that knowledge is dynamic. As new disciplines emerge, as interdisciplinary work blurs traditional boundaries, and as human understanding evolves, classification systems must accommodate these changes gracefully.
The tension between order and flexibility remains central to classification design. A system that is too rigid becomes obsolete; a system with unlimited flexibility becomes unwieldy. The best solutions combine thoughtful notational design, faceted approaches, and strategic foresight by classification designers. Whether through gap devices, sector notation, or sophisticated faceted frameworks, libraries continue to grapple with the challenge of building systems that welcome tomorrow’s knowledge today.
What do you think? How do you think classification systems should balance the need for clear organization with the requirement to accommodate new subjects? In an increasingly interdisciplinary academic environment, are traditional arrays and chains still the best way to organize knowledge, or should libraries adopt entirely new approaches?
References
- https://www.librarianshipstudies.com/2017/11/library-of-congress-classification.html
- https://www.lisedunetwork.com/colon-classification/
- https://www.lisedunetwork.com/characteristics-of-a-good-classification-system/
- https://egyankosh.ac.in/bitstream/123456789/35740/5/Unit-3.pdf
- https://www.lisedunetwork.com/understanding-faceted-classification-in-library-and-information-science/
- https://www.redalyc.org/journal/3843/384357586006/html/
- https://www.lisedunetwork.com/ranganathans-pmest-the-foundation-of-faceted-classification/
- https://ebooks.inflibnet.ac.in/lisp2/chapter/notation-kinds-qualities-mnemonics-and-hospitality/
- https://www.newworldencyclopedia.org/entry/Library_classification
- https://ebooks.inflibnet.ac.in/lisp2/chapter/designing-of-a-depth-classification-schedule-phases-and-steps/
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