Database schema:

CREATE TABLE "Author" (
	"Id" INTEGER -- example: ['9', '14'],
	"Name" TEXT -- example: ['Ernest Jordan', 'K. MORIBE'],
	"Affiliation" TEXT -- example: ['Department of Molecular Biology|School of Science|', 'Cavendish Laboratory|Cambridge University'],
	PRIMARY KEY ("Id")
)


CREATE TABLE "Conference" (
	"Id" INTEGER -- example: ['2', '1'],
	"ShortName" TEXT -- example: ['IADIS', 'IADT'],
	"FullName" TEXT -- example: ['International Association for Development of the I', 'Issues and Applications of Database Technology'],
	"HomePage" TEXT -- example: ['', 'http://www.informatik.uni-trier.de/~ley/db/conf/ia'],
	PRIMARY KEY ("Id")
)


CREATE TABLE "Journal" (
	"Id" INTEGER -- example: ['2', '1'],
	"ShortName" TEXT -- example: ['ICOM', 'AEPIA'],
	"FullName" TEXT -- example: ['Inteligencia Artificial,revista Iberoamericana De ', 'Zeitschrift Für Interaktive Und Kooperative Medien'],
	"HomePage" TEXT -- example: ['http://aepia.dsic.upv.es/revista/', 'http://www.i-com-media.de'],
	PRIMARY KEY ("Id")
)


CREATE TABLE "Paper" (
	"Id" INTEGER -- example: ['2', '1'],
	"Title" TEXT -- example: ['A nonlocal convection–diffusion equation', 'Stitching videos streamed by mobile phones in real'],
	"Year" INTEGER -- example: ['2007', '2009'],
	"ConferenceId" INTEGER -- example: ['0', '167'],
	"JournalId" INTEGER -- example: ['0', '7234'],
	"Keyword" TEXT -- example: ['mobile video capturing|real-time|video stitching', 'Nonlocal diffusion; Convection–diffusion; Asymptot'],
	PRIMARY KEY ("Id"), 
	CONSTRAINT fk_paper_conference FOREIGN KEY("ConferenceId") REFERENCES "Conference" ("Id"),
	CONSTRAINT fk_paper_journal FOREIGN KEY("JournalId") REFERENCES "Journal" ("Id")
)


CREATE TABLE "PaperAuthor" (
	"PaperId" INTEGER -- example: ['5', '4'],
	"AuthorId" INTEGER -- example: ['1102257', '1456512'],
	"Name" TEXT -- example: ['Kazuo Iwama', 'ADAM G. JONES'],
	"Affiliation" TEXT -- example: ['The french National Institute for Research in Comp', 'Kyushu University 812 Fukuoka Japan 812 Fukuoka Ja'],
	CONSTRAINT fk_paperauthor_paper FOREIGN KEY("PaperId") REFERENCES "Paper" ("Id"),
	CONSTRAINT fk_paperauthor_author FOREIGN KEY("AuthorId") REFERENCES "Author" ("Id")
)

Question: How many of the papers are preprinted?
Evidence: year = 0 means this paper is preprint; papers refers to Paper.Id

SQL:
SELECT COUNT(Id) FROM Paper WHERE ConferenceId = 0 AND JournalId = 0