Kolumnaarset

Kolumnaarset is a term found in some Scandinavian technical writings to describe a set of values associated with a single column in columnar data systems. In this sense, a kolumnaarset represents the distinct elements that occur in a given column, potentially together with frequency information or an encoding optimized for columnar storage.

Common implementations use dictionary encoding (mapping distinct values to compact codes), bitmaps indicating presence of a value, or run-length encoding when values repeat contiguously. The kolumnaarset can be stored separately from the full column to speed up set-based operations, such as membership tests, filtering, or set algebra (union, intersection, difference).

In query processing on columnar databases, kolumnaarsets enable rapid pruning and acceleration of operations that depend only on the value domain of a column, rather than on the complete row data. They are often part of broader indexing strategies, including bitmap indexes and dictionary encoding schemes.

Note that there is no universally standardized definition, and the term may be used informally or as a translation for "columnar set" in various languages. It is distinct from the notion of a column in a table or from columnar storage itself, which refers to how data is physically laid out rather than to the set of values.