private RuleBase resolveRuleBase(Query query) {
        String ruleBaseName = query.properties().getString(rulesRulebase);
        if (ruleBaseName == null || ruleBaseName.equals("")) return getDefaultRuleBase();
        RuleBase ruleBase = getRuleBase(ruleBaseName);
        if (ruleBase == null)
            throw new RuleBaseException("Requested rule base '" + ruleBaseName + "' does not exist");
        return ruleBase;
    }
Creates a semantic searcher using the given default rule base
container-search/src/main/java/com/yahoo/prelude/semantics/SemanticSearcher.java