Understanding attributes
Most objects can have generic attributes associated with some of their components. These are organised using an attribute list.
Attribute lists
The generic attributes are defined using the one-of-attribute component schema which is defined as a list where each item is one of the attribute components.
This is usually implemented using an optional attributes property on one or more of geometric components using the attribute-list-property component schema.
For instance the triangle-mesh schema can have attributes attached for both the vertices and indices properties of its triangles property. The dimension of the attribute array in each case corresponds with the length of the geometry property; i.e., one value per vertex in the case of an attribute attached to mesh vertices or one value per triangle in the case of an attribute attached to triangle indices.
In some cases where the geometry is implied the list will have a different name. An example of this is for the regular-grid-3d schema where cell_attributes and vertex_attributes properties are used for attributes for the cells and vertices of the grid respectively.
Attribute definitions
There many attribute types to choose from, depending on the data type (boolean, date, string, integer, etc.).
Most attributes are scalar values but there are also vector, ensemble and time-series values available for some scalar types.
Base properties
The base-attribute component schema defines three required properties (key, name and attribute_type) for all attribute schemas. Each attribute schema will also have a values property with the specific data array for that attribute type.
Additionally, each attribute will typically be classified as a category or continuous attribute and so also have an optional attribute_description property.
Many attribute schemas will also have a required nan_description property to designate not-a-number (NaN) values.
Extra details
Category attributes use the category-attribute schema have a required table property (specified in the category-data component schema). This specifies a lookup table (using the lookup-table element schema) to convert the integer values to strings.
