Provides a fully qualified gml:identifier value of the target
feature. Used primarily to reference a feature by a globally unique
identifier as opposed to the gml:id

The 'actuate' attribute is used to communicate the desired timing 
of traversal from the starting resource to the ending resource; 
it's value should be treated as follows:
onLoad - traverse to the ending resource immediately on loading 
         the starting resource 
onRequest - traverse from the starting resource to the ending 
            resource only on a post-loading event triggered for 
            this purpose 
other - behavior is unconstrained; examine other markup in link 
        for hints 
none - behavior is unconstrained

The 'show' attribute is used to communicate the desired presentation 
of the ending resource on traversal from the starting resource; it's 
value should be treated as follows: 
new - load ending resource in a new window, frame, pane, or other 
      presentation context
replace - load the resource in the same window, frame, pane, or 
          other presentation context
embed - load ending resource in place of the presentation of the 
        starting resource
other - behavior is unconstrained; examine other markup in the 
        link for hints 
none - behavior is unconstrained

The unit of measure for volume or cubic measure.

The unit of measure for volume or cubic measure.

The unit of measure for mass ratio or mass fraction.

The unit of measure for force.

The unit of measure for volume ratio, porosity, or volumetric fraction.

The unit of measure for volume or cubic measure.

The unit of measure for time or duration.

The unit of measure for time or duration.

The unit of measure for density or unit weight. This can be either a mass per volume unit (for true density) or a force per volume unit (for unit weight).

The unit of measure expressed as reciprocal square root of time (e.g., 1/√min, 1/√s, 1/√h). Used in consolidation theory and filtration analysis.

The unit of measure for volume ratio, porosity, or volumetric fraction.

The unit of measure for length or distance.

The unit of measure for pressure, stress, or elastic modulus.

The unit of measure for volume or mass loss. Can be a volume ratio (m3/m3, %, etc.) or a mass ratio (kg/kg, %, etc.). The choice depends on whether volume change or mass change is being measured.

Database handle for the object. It is of XML type ID, so is constrained to be
unique in the XML document within which it occurs. An external identifier for the object in
the form of a URI may be constructed using standard XML and XPointer methods. This is done
by concatenating the URI for the document, a fragment separator, and the value of the id
attribute.