private UriItem instantiateUriItem(String field, OperatorNode<ExpressionOperator> ast) {
        UriItem uriItem = new UriItem(field);

        boolean startAnchorDefault = false;
        boolean endAnchorDefault = indexFactsSession.getIndex(field).isHostIndex();

        if (getAnnotation(ast, START_ANCHOR, Boolean.class, startAnchorDefault,
                          "whether uri matching should be anchored to the start"))
            uriItem.addStartAnchorItem();

        String uriString = ast.<List<OperatorNode<ExpressionOperator>>> getArgument(1).get(0).getArgument(0);
        for (String token : segmenter.segment(uriString, Language.ENGLISH))
            uriItem.addItem(new WordItem(token, field, true));

        if (getAnnotation(ast, END_ANCHOR, Boolean.class, endAnchorDefault,
                          "whether uri matching should be anchored to the end"))
            uriItem.addEndAnchorItem();

        // Aux info to preserve minimal and expected canonical form
        uriItem.setStartAnchorDefault(startAnchorDefault);
        uriItem.setEndAnchorDefault(endAnchorDefault);
        uriItem.setSourceString(uriString);

        return uriItem;
    }
Build a "pure" not, without any positive terms.
container-search/src/main/java/com/yahoo/search/yql/YqlParser.java