我看一段留言板的代码时,看不懂下面的两个意思,那个朋友帮我看看是什么意思??先谢谢了

//留言前的情况
myConnection.ConnectionString="server=.;database=Aspnet;uid=sa;pwd=sa;";
string selCmd1 = "select * from GuestBook where PostID="+postID;
SqlDataAdapter da1 = new SqlDataAdapter(selCmd1,myConnection);

//留言的所有回复者情况
string selCmd2 = "select * from GuestBook where ParentID="+postID;
SqlDataAdapter da2 = new SqlDataAdapter(selCmd2,myConnection);
DataSet ds = new DataSet();
da1.Fill(ds,"host");
da2.Fill(ds,"guest");

请问
da1.Fill(ds,"host");
da2.Fill(ds,"guest");
中的host和guest是什么意思呀??