# 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.