'Given a sequence of catalog selection strings (each is a
catalog name or full path to a catalog .cix file) return a dict
mapping:
<normalized-selector> -> <selection-string>
If "selections" is None, this returns None.'

def _selection_from_selector(self, selections):

    if (selections is None):
        return None
    selection_from_selector = {}
    for selection in selections:
        if isabs(selection):
            selector = normpath(normcase(selection))
        else:
            selector = selection.lower()
        selection_from_selector[selector] = selection
    return selection_from_selector
