CREATE TABLE paper (paperid INT, title VARCHAR, venueid INT, year INT, numciting INT, numcitedby INT, journalid INT)
CREATE TABLE field (fieldid INT)
CREATE TABLE keyphrase (keyphraseid INT, keyphrasename VARCHAR)
CREATE TABLE journal (journalid INT, journalname VARCHAR)
CREATE TABLE dataset (datasetid INT, datasetname VARCHAR)
CREATE TABLE paperdataset (paperid INT, datasetid INT)
CREATE TABLE paperfield (fieldid INT, paperid INT)
CREATE TABLE paperkeyphrase (paperid INT, keyphraseid INT)
CREATE TABLE cite (citingpaperid INT, citedpaperid INT)
CREATE TABLE author (authorid INT, authorname VARCHAR)
CREATE TABLE venue (venueid INT, venuename VARCHAR)
CREATE TABLE writes (paperid INT, authorid INT)

which papers use WordNet or Dbpedia ?
SELECT DISTINCT paper.paperid FROM dataset, paper, paperdataset WHERE dataset.datasetname IN ('WordNet', 'Dbpedia') AND paperdataset.datasetid = dataset.datasetid AND paper.paperid = paperdataset.paperid GROUP BY paper.paperid
SELECT DISTINCT "paper"."paperid" FROM "dataset" JOIN "paperdataset" ON "dataset"."datasetid" = "paperdataset"."datasetid" JOIN "paper" ON "paper"."paperid" = "paperdataset"."paperid" WHERE "dataset"."datasetname" IN ('WordNet', 'Dbpedia') GROUP BY "paper"."paperid"