code: public FieldType getFieldByAlias(FieldTypeClass typeClass, String alias)
     {
        return m_aliasMap.get(new Pair<FieldTypeClass, String>(typeClass, alias));
     }
docs: Retrieve a field from a particular entity using its alias.
  
  @param typeClass the type of entity we are interested in
  @param alias the alias
  @return the field type referred to be the alias, or null if not found