Dewey and Universal decimal classification

To organise books and resources in the Library, we use Dewey decimal classification or Universal Decimal Classification (UDC).


Dewey decimal classification


What do the numbers represent?

Think of the Dewey numbers as representing a subject tree and its branches. Each number represents a particular subject area.

For example, D 574 represents a broad subject area - Biology.

That broad subject area can then be broken down into narrower subject branches, which would be represented by the shelf numbers D 574.1, D 574.2, and so on until D 574.9.

In turn, each of these narrower subject branches may themselves be sub-divided into further narrower branches. For example D 574.1 sub-branches would be represented by the numbers D 574.11, D 574.12, D 574.13 etc.

The D 574.11 subject area could further branch, leading to numbers such as D 574.113, D 574.116 etc.

The longer the number after the decimal point, therefore, the more narrow the subject area it represents.


'J' numbers

Our children's books have a letter 'J' (for 'junior') before their Dewey number.

Items with a 'J' number are shelved in the children's collection on Level 5.


How are the numbers arranged on the shelf?

Going from left to right, general subject numbers come first, followed by their more specific ‘branch’ numbers.

For example, in the D 574 area of the shelves, the plain number D 574 will come first on the shelf, followed by any books with the number representing its first branch D 574.1, and following those, any with numbers representing all of its narrower branches, such as D 574.11, D 574.12 and so on.

Once all the D 574.1… numbers are shelved, they will be followed by any books with the next main branch number D 574.2, followed by all its sub-branch numbers, in the same manner.

Finally, once you have passed all the books with numbers starting with D 574, the sequence moves on to the next main subject area i.e. D 575, and the same pattern is repeated, left to right for its branches and sub-branches.

The sequence runs through one subject area and all of its branches, before moving on to the next subject area. A typical sequence on the shelf, in left to right order, would be:

  • D 574
  • D 574.1
  • D 574.12
  • D 574.122
  • D 574.2
  • D 574.234
  • D 574.5
  • D 574.67
  • D 574.9
  • D 575

Universal Decimal Classification (UDC)

Library serials, government publications, books and serials are classified by UDC. All UDC numbers shelve as decimal numbers - e.g. 5 shelves as 500, 62 shelves after 619 as 620.

UDC symbols shelve in the following order:

+ 621+624
/ 621/622
plain number 621
: 621:622
( ) 621(41)
- 621-79
. 321.1

Please ask a member of Library staff if you need help finding UDC numbers.