求高手解释一段asp代码

<%@ Language=VBScript %>
<%  Option Explicit %>
<% 
' ---------- Page Functions ----------
    Function ChkString(string)
      ChkString = Replace(string, "'", "''")
    End Function

' ---------- Page Variables ----------
    Dim dailyMsg      ' The messgae for that day
    Dim dtCurrentDate       ' The current date being updated
    Dim objConn, strConn, strSQL, objRS ' Database Variables

' ---------- Variable Definitions ----------
    dailyMsg = Request("calendarText")
    dtCurrentDate = Request("currentDate")

    Set objConn = Server.CreateObject("ADODB.Connection")
    strConn = "Provider=Microsoft.Jet.OLEDB.4.0;" & "Data Source=" & Server.MapPath(" b") & ";Persist Security Info=False;"
    objConn.Open(strConn)

    ' Check to see if a message exists, if there is update/add it to the db, if not, delete the message
    If Trim(dailyMsg) = "" then
      StrSql = "DELETE FROM calendar WHERE calendarDate = #" & dtCurrentDate & "#"
    Else
      strSQL = "SELECT * FROM calendar WHERE calendarDate = #" & dtCurrentDate & "#"
      Set objRS = objConn.Execute(strSQL)
      If NOT objRS.EOF Then 
        strSQL = "UPDATE calendar SET calendarText = '" & ChkString(dailyMsg) & "' WHERE calendarDate = #" & dtCurrentDate & "#"
      Else
        strSQL ="INSERT INTO calendar (calendarDate, calendarText) VALUES (#" & dtCurrentDate & "#, '" & ChkString(dailyMsg) & "')"
      End If
    End If

    objConn.Execute(strSQL)
    Set objRS = Nothing
    objConn.Close
    Set objConn = Nothing

    Response.Redirect (" p?currentDate=" & dtCurrentDate)
%>     

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