Whilst working on the recent proposal for Archives (issue #1758 ) a need to describe the extent of items or collections was identified. The discussion reflected similar discussions in the Schema Bib Extend group from many months ago.

It was felt that as this proposal had broader relevance beyond Archives, it would make sense to raise it as a separate issue. However this proposal would add value to the proposal in issue #1758 and they could easily be introduced together.

In Archives, Libraries, Museums, etc., the term 'extent' is used to indicate some aspect of the 'size' of the resource being described. However, measures of 'size' in this context can vary across different types of material, units of measure, and quantity. In the most prevalent metadata formats in these types of organisations, these statements of 'extent' are often strings of text that may bring together several different measures of size, and units.

Examples include "95 linear ft." - "20 folders + 1 VHS videotape .", "1 hard-back volume, 1 sheet.", "149 p.", "300 Items.".

In many cases these strings contain structure that is interpretable by a human eye, but not necessarily representable in structured form.

This proposal attempts to provide at least a property to capture these string values that populate archive, library, and similar systems, while providing the ability to capture structured representation if possible.

Two new properties are proposed:

• collectionSize - Domain: Collection - Range: Integer - "The number of items in the collection"
  This satisfies the simple case of describing the extent of a collection.

• materialExtent - Domain: CreativeWork - Range: Text, QuantitativeValue - "The quantity of the materials being described or an expression of the physical space they occupy"

There is an in-depth outline of the proposal on the Schema Architypes Wiki which includes references to relevant standards such as Marc, EAD, ISAD(G)

Included are some examples for materialExtent:
Text only:

<script type="application/ld+json">
{
  "@context": "http://schema.org",
  "@type": ["CreativeWork","ArchiveComponent"],
  "materialExtent": "285 A boxes, 8 OS boxes (plus 45 T boxes, 50 A boxes, 13 OS boxes / items uncatalogued)"
}
</script>

Single Structured Value:

<script type="application/ld+json">
{
  "@context": "http://schema.org",
  "@type": ["CreativeWork","ArchiveComponent"],
  "materialExtent": {
            "@type": "QuantitativeValue",
            "unitText": "folder",
            "value": "1"
          }
}
</script>

Multiple Structured Values:

<script type="application/ld+json">
{
  "@context": "http://schema.org",
  "@type": ["CreativeWork","ArchiveComponent"],
  "materialExtent": [
          {
            "@type": "QuantitativeValue",
            "unitText": "folder",
            "value": "1"
          },
          {
            "@type": "QuantitativeValue",
            "unitText": "design drawings",
            "value": "5"
          }
       ]
}
</script>