public interface ValueMap
 A valueMap can be specified as either an Array of legal values, or as an
 Object where each property maps a stored value to a user-displayable value.  See DataSourceField.valueMap for how to express a ValueMap in Component XML. 
A ValueMap can be entirely static or entirely dynamic, with many options in between. For example, a ValueMap may be:
DataSource.fetchData()
 where a valueMap is derived dynamically from the returned data (see DataSource.fetchData() for an example).  Such a valueMap may be updated at any time, for example, every time the user
 changes a related field while editing data. Smart
 GWT Architecture Overview to understand the best architecture from a performance and caching perspective.