nested/hierarchical dimensions

[nkrishnaswami]

Many dimensions, for example state/county/city or sector/industry group/industry/subindustry (eg GICS), have parent/child or broader/narrower relationships between dimension values at each level. Other schemes like SKOS or DSPL 1.0 can model this, but DSPL 2.0 does not yet include such a facility.

In this issue, discuss what such an extension could look like.

[nkrishnaswami]

Something like this, perhaps:

HierarchicalDimension

Type: Thing > Intangible > CategoricalDimension > HierarchicalDimension

Hierarchical dimensions define the categories that measures can apply to when these are nested within other dimensions. For instance, countries, industry/sector schemes, age groups, etc.

Property	Expected type	Description
parentDimension	CategoricalDimension	The ID of the parent or containing dimension.

When the codeList is a CSV table, it must include a column parent, which contains the codeValue of a DimensionValue defined in the parentDimension.

When the codeList is not a CSV table, each DimensionValue must include an additionalProperty with propertyID of parent and with value being the codeValue of a DimensionValue defined in the parentDimension.

[nkrishnaswami]

After discussion, it adds unnecessary complexity to introduce a new type -- every property is optional in schema.org, so we can simply omit parentDimension when there is not one. Also schema:parent refers to the parents of beings, so we introduce 'parentValue' for a parent DimensionValue.
In keeping with "things not strings", the parentValue property has a range of DimensionValue, which can either be an object sharing a codeValue with or a URL referring by ID to the parent DimensionValue.