The `equivalence`

sheet is optional and specifies the units of the
nomenclature that have equivalences in other nomenclatures supported by the Database. These
links with other nomenclatures are used to make automatic conversions of statistical data
between nomenclatures.

An equivalence is a particular case of a derivation, whose the relationship value is |

The condition of the validity of this file is the support of the referenced nomenclature and its version by the Database.

It is not necessary to establish equivalence links with the units of other versions of the same nomenclature. This will be automatically done during the integration of the nomenclature into the library.

Two statistical units are considered to be equivalent if they are equal semantically (a country referenced by a nomenclature may be equivalent to a country in another one, but not to a group of countries) and geographically (both the units have the same shape and boundaries).

The `equivalence`

sheet must respect the layout shown in Table 2.10
(examples of values are given in *italics*).

**Table 2.10. Equivalence sheet layout example**

A | B | C | D | E | F | |

1 | unit_code | unit_level | equivalent_unit_code | equivalent_unit_level | equivalent_nomenclature | equivalent_version |

2 | BE | 0 | BE | 1 | ISO3166 | 2006 |

3 | BE | 0 | W11122 | 5 | WUTS | 2007 |

4 | BE | 0 | 88 | 3 | UNEP | 2006 |

Details on the columns are given below:

`unit_code`

MANDATORY

References the code of the statistical unit present into the

`units`

sheet. Theoretically, a statistical unit can be equivalent to any number of statistical units in other nomenclatures. The expected value in this column is a`character string`

that is also present in the`units`

sheet (see Section 2.3).`unit_level`

MANDATORY

References the level of the statistical unit present into the

`version`

sheet. An empty value references the default level of a non-hierarchical nomenclature.`equivalent_unit_code`

MANDATORY

References the code of the equivalent unit valid in another nomenclature. The expected value in this column must be a statistical unit code already registered by the Database.

`equivalent_unit_level`

MANDATORY

References the level of the equivalent unit. An empty value references the default level of a non-hierarchical nomenclature.

`equivalent_nomenclature`

MANDATORY

References the nomenclature to which belongs the unit code in the previous column. The expected value in this column must be an acronym of a nomenclature supported by the Database [1].

`equivalent_version`

MANDATORY

References the version of the nomenclature mentioned in the previous column, where the equivalence between the units is established. The expected value must be an identifier of a nomenclature version supported by the Database [1].

*Data constraints.* Any combination of `unit_code`

+
`equivalent_nomenclature`

+ `equivalent_version`

is unique
in this table.