96. A Correspondence Table expresses the relationship between two Statistical Classifications. These relationships show how the items of the source/predecessor Statistical Classification relate to the items of the target/successor Statistical Classification. The typology presented in this appendix provides a systematic way to classify the various types of relationships, and thus enables to enrich the information held in Correspondence Tables.
97. Before presenting the typology, we have to make clear what we understand by "change of a Classification Item".
2. Features of Item Change
98. A Classification Item is the designation of a category of a Statistical Classification. It can be said to consist of three components:
- a code
- a name (official title)
- a definition, which is:
- expressed in explanatory notes, index entries and case law,
- expressed in the set of statistical objects/units, belonging to the category. This is the denotation of the category.
99. From these three components, the definition represents the essence of the category best, more than the name and the code. Therefore, we will consider the meaning of a category to be represented by its definition, especially its denotation.
100. Ideally, naming, coding and definition ought to behave consistently, while the definition is "leading", in the sense that a change of definition 1 should necessarily imply a change of code and name, while conversely a code or name may only change if accompanied by a meaning change. In practice, however it may occur that a code or a name of an item changes while its definition remains the same, or the other way around. The typology should account for such situations. This is done by distinguishing between real change and virtual change. Where real change stands for changes in meaning, whether or not accompanied by changes in naming and/or coding, while virtual change stands for changes in coding and/or naming, while the meaning remains the same.
3. A Typology of Item Changes
101. The figures show the relationships between Classification Items involved in the change from the old (left) to the new (right) Statistical Classification. Blocks denote Classification Items. Classification Items are identified by their code. A block that keeps its colour keeps its code. The various changes are expressed in terms of events.
A. REAL CHANGE
A.1. Deletion (1 : 0)
A Classification Item expires, while its denotation reduces to zero; it does not proceed as (part of the) denotation of one or more other (existing) Classification Items.
A.2 Creation (0 : 1)
The mirror image of deletion: a Classification Item emerges, while its denotation is not (part of) the denotation of one or more existing Classification Items.
A.3 COMBINATION (N:1)
Two or more Classification Items expire, while their denotations proceed in one emerging Classification Item.
A.3.2 TAKE-OVER (N: 1)
A Classification Item expires, while its denotation proceeds as part of the denotation of another Classification Item, which continues its existence.
A.4 Decomposition (1: N)
The mirror image of merger: a Classification Item expires, while its denotation is distributed over and proceeds in two or more emerging Classification Items.
A.4.2 SPLIT OFF
The mirror image of take-over: a Classification Item continues to exist, while part of its denotation moves to another (emerging) Classification Item.
A.5 Transfer (M : N
Part of the denotation of a Classification Item moves to another (existing) Classification Item
- The situation pictured is the most simple of a number of situations, in which more Classification Items may be involved in the relationship between the old and new structure.
- "Transfer" can also be applied at higher Levels of a Statistical Classification. In such cases the part of the denotation that moves (to another (existing) Classification Item) corresponds to a Classification Item at the lower Level:
B. VIRTUAL CHANGE
B. 1 CODE CHANGE
(1: 0 ; 0 : 1)
A Classification Item expires, while its denotation proceeds as the denotation of an emerging Classification Item.
B.2 NAME CHANGE (1 : 1)
The name of a Classification Item changes, while its denotation remains the same.
103. Deletion and creation may result in border changes. Combination, decomposition and transfer do result in border changes. Code change and name change do not result in border changes.