/**
* Used to indicate "natural" sorting order, usually according
* FID (hopefully based on Key attribtues).
* <p>
* This is the order that is most likely to be available in optimzied
* form, if an Attribute is marked as "key" an optimized ordering should
* be considered avaialble.
* </p>
* <p>
* Non optimized orderings are will at the very least require as pass
* through the data to bring it into memory, you can assume somekind
* of TreeSet would be used. Where the nodes in the tree would indicate
* a list of FeatureIds assoicated with the node, in the order encountered.
* </p>
* <p>
* This is a "NullObject".
* </p>
*/
SortBy NATURAL_ORDER = new NullSortBy(SortOrder.ASCENDING);