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 __update_covariance(self, means, rc, mc):
        covariance = 0.0
        for index_point in range(len(self.__data)):
            deviation = numpy.array([self.__data[index_point] - means])
            covariance += rc[index_point] * deviation.T.dot(deviation)