'Right to exist'
At a special service in Turin's main synagogue, Somekh said the tribute marked not only the state of Israel's 60 years but also "4,000 years of our presence on the world stage as 'People of the Book'."
Napolitano arrived by helicopter along with Israeli novelist Abraham B Yehoshua on Wednesday morning to cut the inaugural ribbon.
"No dialogue is possible if there is a refusal to recognise Israel," the president said.
There can be no "rejection of the reasons for its birth or of its right to exist in peace and security".
Israel's stand at the fair was attended by hundreds of people, many draped in the Israeli flag, with one group holding a banner reading 'I feel Jewish today'.
Shortly after Napolitano's arrival, security forces prevented a small group of pro-Palestinian activists from displaying a banner outside the venue.
They moved to a side street to display the banner reading "No to Zionist Colonialism, Boycott Israel, Boycott the 2008 Book Fair".
Ahead of the five-day event, several Muslim writers, intellectuals and artists as well as the Free Palestine association staged a two-day protest seminar at the University of Turin entitled Western Democracies and Ethnic Cleansing in Palestine.
Aharon Shabtai, an Israeli poet, also refused to attend the event, saying it was "purely another occasion for Israel to make propaganda and gain more support for its military occupation" of the Palestinian territories.
A week ago, far-left activists in Turin burned Israeli and US flags after the traditional May Day march.
Free Palestine is planning a protest on Saturday.
Organisers of the book fair say they expect about 300 people to take part in the Saturday protest, while activist Sergio Cararo of the Palestine Forum predicted there would be at least 10,000.
Cararo said: "We asked the organisers and promoters for equal dignity for both Israelis and Palestinians, but no compromise was found, so we started the campaign to boycott."
Security has been tightened for this year's event, coming two months after the Paris book fair which was inaugurated by Shimon Peres, the Israeli president, and marred by boycotts and a bomb threat that forced an hour-long evacuation of the venue.
Critics say Israel should not be rewarded in this manner while it faces international condemnation over its actions in the Palestinian territories.
Every year, as Israel celebrates its anniversary, the Palestinians remember the 700,000 of their fellow citizens who fled or were forced from their homes as the Jewish state was created.
They and their descendants now form a UN-registered refugee population of more than 4.5 million people.
More than 300,000 people visited last year's book fair in Turin.
This year the event is expected to attract about 1,400 publishers, both Italian and foreign, which Rolando Picchioni, the fair's director, said was an "absolute record".