4.2.5.2 IDL

   //File: DAISDAIO.idl#ifndef _DAIS_DAIO_IDL#define _DAIS_DAIO_IDL#pragma prefix "omg.org"#include <DAISCommon.idl>

   module DAIS {

   module DataAccess {module IO {

   enum DataSource { DS_CACHE, DS_DEVICE

   };

   struct ItemState

   { SimpleValue value; DateTime time_stamp; Quality dais_quality; ClientItemHandle client_handle;

   };typedef sequence<ItemState> ItemStates;

   struct ItemUpdate

   { ServerItemHandle server_handle; SimpleValue value;

   };typedef sequence<ItemUpdate> ItemUpdates;

   interface SyncIO{

   ItemStates sync_read ( in DataSource data_source, in ServerItemHandles server_handles, out ItemErrors errors

   );

   ItemErrors sync_write (

   exception NotConnected{string reason;}; exception InvalidCancelID{string reason;}; exception NotActive{string reason;};

   CancelID async_read ( in ServerItemHandles server_handles, in DataSource data_source, in unsigned long transaction_id

   ) raises (NotConnected, NotActive);

   CancelID async_write ( in ItemUpdates updates,

   in unsigned long transaction_id ) raises (NotConnected);

   CancelID refresh (

   in DataSource data_source, ) raises (NotConnected,NotActive);

   void cancel ( in CancelID cancel_id in unsigned long transaction_id

   ) raises (InvalidCancelID);

   attribute boolean enabled; };

   interface Callback {

   void on_data_change ( in unsigned long transaction_id, in boolean all_quality_good, in ItemStates states

   );

   void on_read_complete ( in unsigned long transaction_id, in boolean all_quality_good, in ItemStates states, in ItemErrors errors

   );

   void on_write_complete ( in unsigned long transaction_id, in ItemErrors errors

   );

   void on_cancel_complete (

   interface ConnectionPoint {

   attribute Callback cllbck; };};};}; #endif // _DAIS_DAIO_IDL DataSource

   ItemState

   The struct is the major carrier of data conveyed over the interface. It is the “message? holding the payload.

   ItemUpdate

   The struct carry an update for an item.

   SyncIO

   An interface for the synchronous operations.

   sync_read()

   Synchronous read of items. Inactive items will be reported with OPCQuality set to OPC_QUALITY_OUT_OF_SERVICE.

   sync_write()

   Synchronous write of item values to devices (not the internal server cache). The active state of the group or the items is ignored.

   AsyncIO

   An interface for asynchronous read or write operations.

   NotConnected

   An exception telling that there is no callback object connected by the client.

   InvalidCancelID

   An exception telling that the supplied cancel id number is not recognized.

   NotActive

   An exception telling that the group or all items in the group is inactive. Only issued when read from cache.

   async_read()

   Asynchronous read of items from devices. OPC may report read errors both at return from async_read() and at on_read_complete(). DAIS will report all errors at on_read_complete()..

   async_write()

   Asynchronous write of item values to devices (not the internal server cache). OPC may report write errors both at return from async_write() and at on_write_complete(). DAIS will report all errors at on_write_complete().

   refresh()

   Initiate a complete asynchronous read transfer for all item entries defined via the DAIS::DataAccess::GroupEntry::Manager interface. Inactive items will be reported with OPCQuality set to OPC_QUALITY_OUT_OF_SERVICE.

   The cyclic on_data_change reporting continues unaffected by a refresh call. However, items still unchanged after a refresh will not be reported in a succeeding on_data_change call.

   cancel()

   Cancel on ongoing refresh, async read, or async write operations. The server is expected to acknowledge a successfully initiated cancel operation with an on_cancel_complete() callback.

   enable

   An attribute used to enable or disable the spontaneous on_data_change() callbacks. The enable state does not affect on data change response to refresh calls. When a group is created it is enabled by default.

   Callback

   An interface implemented by the client and used by the server to send data to the client.

   on_data_change()

   The method is called by the server when spontaneous changes occur or when the client has requested an explicit refresh. Only active items are reported in spontaneous calls.

   on_read_complete()

   The method is used by the server to report data in response to an asynchronous read.

   on_write_complete()

   The method is used to report the success of an asynchronous write operation.

   on_cancel_complete()

   The method is used to acknowledge the completion of a successfully initiated cancel call.

   ConnectionPoint

   An interface used by the client to connect or disconnect a client callback object at the server.

   callback

   An attribute referencing the callback object.

   In an implementation one get and one set method will implement the callback attribute. Due to limitation in the UML tool used to draw the diagrams, the attribute is represented by the two methods connect and disconnect.