The symbols chosen for a UDC notation are language independent and universally recognizable - the arabic numerals, supplemented by a few other signs familiar from mathematics and ordinary punctuation. The signs and symbols in UDC are used to break the number sequence and allow the separation (i.e. parsing of) pre-combined concepts into constituent simple concepts.
UDC uses a decimal, hierarchically and syntactically expressive notation.
The arrangement is based on the decimal system: every number is thought of as a decimal fraction with the initial point omitted, and this determines the filing order, but, for ease of reading, it is usually punctuated after every third digit. Thus, after 61 'Medical sciences' come the subdivisions 611 to 619; under 611 'Anatomy' come its subdivisions 611.1 to 611.9; under 611.1 come all of its subdivisions before 611.2 occurs, and so on; after 619 comes 62. One advantage of this system is that it is infinitely extensible, and when new subdivisions are introduced, they need not disturb the existing allocation of numbers.
Hierarchically expressive notation
UDC notation is hierarchically expressive. Hierarchically expressive notation mirrors the hierarchy and each digit or letter of the notation will represent one level in division. The deeper in the hierarchy the concept is, the longer the notation. Classifications with hierarchically expressive notations are much friendlier to navigate and use. When presenting a classification hierarchy in print or online there will be no need to show the indentation of subordinate classes as this will be obvious from the notation itself, e.g.
|599.744||Canidae. Ursidae. Musteloidea|
|599.744.211||Brown bears (grizzly)|
Syntactically expressive notation
UDC is an analytico-synthetic classification. This means that individual UDC classmarks can be used to build more complex expressions similar to the way we use words to create complex sentences. Special symbols that are used to connect, start or end simple UDC numbers enable the parsing and understanding of complex expressions. This type of notational system is called syntactically-expressive notation. The synthesis of UDC numbers follow fixed syntactic rules that are valid and can be applied to the entire UDC system. Because of the syntactic rules and strict application of notational symbols, UDC complex expressions can be deconstructed accurately into simple UDC numbers.
|599.744.212||Polar bear (main number)|
|57.017.7||Respiration. Metabolism (special auxiliary number)|
|"327.502"||February (common auxiliary number of time)|
This can be combined as 599.744.212.017.7"327.502" , meaning: polar bears - metabolism - month of February.