The unit of measure for particle size. Can be a linear dimension (mm, μm, cm, in) or phi units. When using phi units, smaller values represent larger particles (e.g., -1 phi = 2mm, 0 phi = 1mm, 4 phi = 0.0625mm).
Database handle for the object. It is of XML type ID, so is constrained to beunique in the XML document within which it occurs. An external identifier for the object inthe form of a URI may be constructed using standard XML and XPointer methods. This is doneby concatenating the URI for the document, a fragment separator, and the value of the idattribute.