INFO: Comparing RDS Technology to RDO and DAO

• Microsoft Internet Information Server version 3.0
• Microsoft Remote Data Service versions 1.0, 1.1, and 1.5

SUMMARY

NOTE: With version 1.5, the Remote Data Service (RDS) was renamed and merged with ActiveX Data Objects (ADO) to provide data remoting within the same programming model as ADO. Formerly, the Remote Data Service was known as the Advanced Data Connector (ADC). To clarify the relationship of ADC to ADO, ADC is now known as the Remote Data Service (RDS), a feature of ADO.

Q. Is the Advanced Data Connector superior to RDO and DAO in getting at SQL

   data in a client-server application?

   your database server. The Remote Data Service (RDS) works
   disconnected via HTTP over your intranet or the Internet through
   firewalls. RDS also works over DCOM but this discussion focuses on HTTP.

   RDS passes a disconnected recordset to the client. This is a completely
   stateless model, which means the server could actually be shut down and
   restarted between RDS client requests. This is done via a Mime64 encoded
   ADTG (Advanced Data Tablegram) passed to the client, which then
   opens it and loads it into a client-side VTM (Virtual Table
   Manager). At this time the client can walk the recordset, perform
   updates, and send the changes back to the server for base table updates.

   RDO and DAO work in-process on the local machine or possibly over a LAN
   via DCOM if you wrap their functionality in a Visual Basic ActiveX EXE.
   Currently DCOM does not support transport over HTTP so it is impossible
   to pass a recordset through a firewall. Attempting to marshal a
   recordset and its interfaces over DCOM to the client is also
   unacceptably slow and will ultimately fail. Your alternative is to pass
   the recordset from the server to the client as a variant array
   (GetRows), which works well, but is very primitive compared to RDS
   technology.

   RDS also provides the support necessary to bind to data-aware OCXs in
   Microsoft Internet Explorer 3.0 (IE3), support that is not built into
   IE3. This data binding functionality is very similar to the Visual Basic
   Data Control and Remote Data Control, which require very little or no
   code.

MORE INFORMATION

The following example code demonstrates how the RDS can retrieve disconnected recordsets over the Internet from a Visual Basic program.

Although late binding to the AdvancedDataSpace is used in this example to keep it simple, you may want to consider early binding because it provides two big wins: performance and type checking. The performance may not be noticeable, but the improvements in the type checking and the robustness of the run-time error checking make it worthwhile.

   Dim RS As Object    'Disconnected Recordset
   Dim ADS As Object   'AdvancedDataSpace
   Dim ADF As Object   'AdvancedDataFactory

   Private Sub Form_Load()
      Set ADS = CreateObject("AdvancedDataSpace")
      Set ADF = ADS.CreateObject("AdvancedDataFactory", _
         "http://www.myserver.com")

      'This query returns a recordset over HTTP
      Dim strCn As Variant, strSQL As Variant
      strCn = "dsn=pubs;uid=sa;pwd="
      strSQL = "Select * From Authors"
      Set RS = ADF.Query(strCn, strSQL)
      RS.MoveNext           'Walk Recordset
      Debug.Print RS(0)     'Print Row 1, Col 1 to Debug Window
   End Sub

REFERENCES

For a more detailed example of this code, please see the following article in the Microsoft Knowledge Base:

ARTICLE-ID: Q165297

TITLE     : RDS: How To Use From Inside a Visual Basic Program

RDS Help, Mrds10.hlp (contained in the self-extracting RDS installation file, Mrds10.exe).

(c) Microsoft Corporation 1997, All Rights Reserved. Contributions by Jon Fowler, Microsoft Corporation

Keywords          : VBKBADC VBKBDB VBKBInet
Version           : 3.0 1.0 1.1 1.5
Platform          : NT WINDOWS
Issue type        : kbhowto