A WebServiceDataCacheNode represents a single node in the doubly-linked list holding the data for a WebServiceDataCache. The WebServiceDataCacheNode has an array of data (which may actually be null, if the node's data has not yet been loaded), next and prev pointers to the next and previous nodes in the linked list, and coveredMin and coveredMax values that indicate the min and max values of the "covered" range of data for this node.

The "covered" range is the interval of the data number line for which this node is responsible for storing data; Multigraph uses range this to avoid requesting the same data twice --- it never requests data for a range already covered by an existing cache node.

Initially, when the WebServiceDataCacheNode is created, the limits of the covered range are specified in the constructor. Later on, when the node's data is actually populated, the limits are potentially adjusted outward, if the range of data received is larger than the initially specified covered range. So in all cases, the covered range indicates the range for which no more data is needed, because it's covered by this node.

Note that the covered range is never adjusted to be smaller.

The WebServiceDataCacheNode does not actually fetch any data --- it is simply a storage container for fetched data; it's up to other code outside of this object to fetch and populate the data.