def insertDomain(self, domain, indegree=0, outdegree=0):
		'''增加一个域名'''
		cur = self.conn.cursor()
		cur.execute("INSERT INTO Domains VALUES (NULL,?,?,?)", (domain, indegree, outdegree))
		# 写入到文件中
		self.conn.commit()
def gaussian(data, mean, covariance):
    """!
    @brief Calculates gaussian for dataset using specified mean (mathematical expectation) and variance or covariance in case
            multi-dimensional data.