private Map<String, String> asExpressionStrings(Map<String, RankingExpression> map) {
        HashMap<String, String> values = new HashMap<>();
        for (Map.Entry<String, RankingExpression> entry : map.entrySet())
            values.put(entry.getKey(), entry.getValue().getRoot().toString());
        return values;
    }
Returns all the output expressions of this indexed by name. The names consist of one or two parts
separated by dot, where the first part is the signature name
if signatures are used, or the expression name if signatures are not used and there are multiple
expressions, and the second is the output name if signature names are used.
model-integration/src/main/java/ai/vespa/rankingexpression/importer/ImportedModel.java