Generalize feature property characteristics

[desruisseaux]

ISO 19109 defines characterizeBy on feature attribute type. This is used for storing additional information with an attribute. For example, an attribute that carries air temperature may have another attribute that holds the measurement accuracy. For example, in 10 ± 0.1°C, 10 is the attribute value and 0.1 is a characteristic of the attribute (the unit of measurement can also be another characteristic).

GeoAPI represents characteristics with a characteristics() methods in org.opengis.feature.Attribute and AttributeType interfaces. However, the S-100 international standard used in hydrography applies characteristics not only on feature attributes, but also on feature associations, which are represented in GeoAPI by the FeatureAssociation interface. For addressing S-100 need, we propose to:

• Move the characteristics() method from the Feature interface to its Property parent interface.
• Move the characteristics() method from the FeatureType interface to its PropertyType parent interface.

It would allow to apply characteristics on all types of feature properties: attributes, associations and operations.