What is the lightweight value with no information model and the flexible value is unknown?
CREATE TABLE "popular_languages_used_for_data_exchange" (
  "schemas" text,
  "flexible" text,
  "semantic_verification" text,
  "dictionary" text,
  "information_model" text,
  "synonyms_and_homonyms" text,
  "dialecting" text,
  "web_standard" text,
  "transformations" text,
  "lightweight" text,
  "human_readable" text
);
SELECT "lightweight" FROM "popular_languages_used_for_data_exchange" WHERE "information_model"='no' AND "flexible"='unknown';