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ADS Overview

Advantage Database Server RDD
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 Description

      RDDADS is an RDD for the Advantage Database Server, an xBase data
      server by Extended Systems <www.advantagedatabase.com>.  The RDD
      was written by Alexander Kresin <alex@belacy.belgorod.su>
      Additional code and documentation was added by  Brian Hays
      <bhays@abacuslaw.com>.

      Your Harbour application can access a remote database server for a
      true client/server architecture, or it can use the "local server"
      ADSLOC32.DLL for stand-alone or even small network installations.

      For using this RDD you need to have:   
      ACE32.DLL    ( Advantage Client Engine ),   
      AXCWS32.DLL  ( communication layer for remote server ) or   
      ADSLOC32.DLL ( local server )   

      You need also to create ace32.lib with the help of implib.exe:
      implib ace32.lib ace32.dll

      Then build rddads.lib using make_b32.bat or make_vc.bat.

      For building executables don't forget to include the ace32.lib and
      rddads.lib in the make file or link script.

      You also need to include in your PRG file following lines:

      REQUEST _ADS
      rddRegister( "ADS", 1 )
      rddsetdefault( "ADS" )

      By default RDDADS is tuned for remote server and cdx indexes. To
      change this you may use these commands defined in ads.ch:

      SET SERVER LOCAL  SET SERVER REMOTE

      SET FILETYPE TO NTX  SET FILETYPE TO ADT  SET FILETYPE TO CDX

      or functions AdsSetServerType(), AdsSetFileType().  See the header
      file ADS.CH for details.

      Note that the default local server (ADSLOC32.DLL) is useable for
      file sharing on a small network.  The default DLL is limited to  5
      users, but an unlimited version is available from Extended Systems.

      MAX OPEN TABLES: The server (even local) has its own setting for  Max
      Tables allowed open.  For the Local Server, it can be set in
      ADSLOCAL.CFG.  The default is only 50!  For the Windows Remote
      Servers, use the Configuration Utility, or  increase the setting for
      the TABLES configuration value in the Advantage  Database Server
      configuration registry key using the Registry Editor.  For NetWare,
      edit the configuration file ADS.CFG.

      See ACE.HLP under ADSLOCAL.CFG, or the Advantage Error Guide for
      error 7005.

      Every attempt has been made to make the rdd compliant with the
      standard dbfcdx rdd at the .PRG level.  One important difference is
      the handling of structural indexes.  ACE will  always
      automatically open an index with the same  name as the data file.
      There is no way to turn this feature off.

      Be sure to use the command SET DEFAULT TO (cDir) and not its
      equivalent Set() function call. The Set() function will not make
      the call to ADS to change its internal setting, but the command
      will. The same is true for DATEFORMAT, DELETE, and EPOCH.

      For programmers who are already familiar with the  ACE engine, this
      also means there are some differences  between the RDDADS in
      Harbour and the parallel ACE documentation.

      1) In ACE, skipping backwards to BOF goes to the phantom record and
      sets the record number to 0.  In RDDADS, the  record pointer stays
      at  the Top record and only the BOF flag is set to True.

      2) In RDDADS, a filter expression can be used that may not be  valid
      on the server (because of references to public variables or
      User-Defined Functions).  In these cases, all data will come back
      from the server  but will be filtered by the application running on
      the client.  These situations lose the benefits of having a data
      server and should  be avoided, but they will function as they would
      in a Clipper program.

      One problem with this scenario is that index key counting  functions
      that are supposed to give an accurate count respecting  the filter
      (e.g. dbOrderInfo(DBOI_KEYCOUNT) will return the values the  Server
      knows about, so the counts will be inaccurate.

      3) When setting a relation, the expression must be one that can be
      evaluated by the Advantage Expression Engine.  UDFs will fail.