Lonclass and UDC (like DDC) are expressed using codes based on decimal numbers.
Unlike DDC, the Lonclass and UDC codes use additional punctuation to express patterns of relationships and re-usable qualifiers.
While Lonclass makes a few structural adjustments to the UDC system to support its emphasis on TV and radio content, its main distinction is in the actual set of topics that are recorded within its authority file and within specific BBC catalogue records.
Unlike UDC and DDC, which are widely used across the library community, Lonclass has remained a BBC-internal system since its creation in the 1960s.
[2] For example, a Lonclass or UDC code may represent "Report on the environmental impact of the decline of tin mining in Sweden in the 20th century".