Harmonize ISO 19157 parameter class

[desruisseaux]

ISO 19157 defines a DQM_Parameter class (added in #44), which duplicates the parameter classes provided by other standards:

• ISO 19111 CC_OperationParameter
• ISO 19115 SV_Parameter (referenced by OperationMetadata.getParameters())
• ISO 19157 DQM_Parameter (referenced only in Measure.getParameters())
• Possibly WPS in a future version, etc.

GeoAPI tries to consolidate all parameters API in a single org.opengis.parameter package. If we apply this consolidation to ISO 19157 as well, then the SV_Parameter class should be omitted in favour of org.opengis.parameter.ParameterDescriptor (I didn't found the parameter value anywhere in ISO 19157). The mapping would be:

ISO 19157	ParameterDescriptor	Change of value type
name	getName()	InternationalString → Identifier
definition	getName().getDescription()
description	getDescription()	Description → InternationalString
valueType	getValueClass()	RecordType → Class<?>
valueStructure	To be omitted?

The valueStructure attribute may be omitted because in an object-oriented language, we rather expect the valueType to be the structure, for example org.opengis.referencing.operation.Matrix.

[desruisseaux]

For the record, a Java interface derived verbatim from ISO 19157 would be like below (slightly simplified):

/**
 * Data quality parameter.
 *
 * @version 3.1
 * @since   3.1
 */
@UML(identifier="DQM_Parameter", specification=ISO_19157)
public interface Parameter {
    /**
     * Name of the data quality parameter.
     */
    @UML(identifier="name", obligation=MANDATORY, specification=ISO_19157)
    InternationalString getName();

    /**
     * Definition of the data quality parameter.
     */
    @UML(identifier="definition", obligation=MANDATORY, specification=ISO_19157)
    InternationalString getDefinition();

    /**
     * Description of the data quality parameter.
     */
    @UML(identifier="description", obligation=OPTIONAL, specification=ISO_19157)
    Description getDescription();

    /**
     * Value type of the data quality parameter.
     */
    @UML(identifier="valueType", obligation=MANDATORY, specification=ISO_19157)
    TypeName getValueType();

    /**
     * Structure of the data quality parameter.
     */
    @UML(identifier="valueStructure", obligation=OPTIONAL, specification=ISO_19157)
    ValueStructure getValueStructure();
}

[desruisseaux]

We still have an open issue about DQM_Description. In current version, the extendedDescription property (a BrowseGraphic) is lost. This is tracked in separated issue #78.

Regarding whether to omit ValueStructure, current version keeps it despite the fact that it now appears at only one location. If we omitted that property, it would have to be replaced by some method returning a Class<?>. So it would not really simplify the Measure interface. Keeping ValueStructure does the same functionality in a more controlled way (the set of valid types is more explicit).