Attribute-Value Field

An attribute-value field collects a set of user-supplied attribute/value pairs. The instance author names each attribute and gives its value, so the field suits metadata whose properties are not known when the template is designed. In YAML its type is attribute-value-field.

The definition takes no type-specific keys, since the attribute names are not known until the instance is filled in.

- key: "extra-attributes"
  type: attribute-value-field
  name: "Additional Characteristics"

In an Instance

An attribute-value field is represented differently from other fields in instances. Its values do not sit under the instance's children. Instead the field's key becomes a top-level key of the instance, and beneath it each attribute the author supplied is paired with its value. Those attribute names are chosen by the author at fill-in time, not fixed by the template.

type: instance
name: "SDY232"
isBasedOn: "https://repo.metadatacenter.org/templates/ec3f500"
children:
  study-name:
    value: "Cardiology cohort"
extra-attributes:
  Batch Number:
    value: "3"
  Freezer ID:
    value: "F-12"

A parent may hold more than one attribute-value field. Each appears as its own top-level key, keyed by the field's key, carrying its own set of attribute-value pairs.

extra-attributes:
  Batch Number:
    value: "3"
storage-details:
  Freezer ID:
    value: "F-12"
  Shelf:
    value: "4"

Reserved Keys

An attribute-value field's key is written beside its parent's own keys rather than under children, so it may not be one of them. The reserved keys depend on the parent. In a template, the field sits beside every key of the instance: type, name, description, id, instanceType, isBasedOn, derivedFrom, children, annotations, createdOn, createdBy, modifiedOn and modifiedBy. In an element, the field sits beside the keys of an element instance, which can be written nested in its parent or on its own, so it may take none of the keys of either form: type, name, description, id, instanceType, children, createdOn, createdBy, modifiedOn and modifiedBy.

These reservations add to the reserved child keys that apply to every field and element. The attribute names an instance author supplies are subject only to the latter. An attribute may be called type, for example, because it is written beneath the field's key.