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View Ref-File13.8  OLGA protocol                                                TOS

The OLGA protocol (Object Linking for GEM Applications) was developed 
by Thomas Much, and permits object linking under GEM too.

As this concept may not be familiar to all readers, first a possible 
example of its application: Imagine you are using your text processor 
and would like to enhance your document with a graphic. After placing 
your graphic in the text, you decide to alter it slightly. Normally 
you would have to switch over to your graphics program, perform the 
desired changes there, switch back to the text processor, discard the 
old graphic, then import and position the new one. But if both of the 
applications (i.e. graphics program and text processor) support the 
OLGA protocol, the solution of this task could look as follows: You 
switch to the graphics program, modify the graphic there, and after 
saving it you are finished! Because the text processor automatically 
recognizes that the graphic has been altered, and itself replaces it 
in the document!

The above example presupposes a multitasking operating system such as 
MagiC or MultiTOS. And in fact: Single-TOS systems are not supported 
by OLGA (since Rev. 1.0 - earlier versions could also be run as desk 
accessories.) Those wanting to involve themselves closer with the OLGA 
protocol should take note of the following points:

   . Initialization and termination
   . Functions of a Server
   . Functions of a Client
   . The Info file format

OLGA works in a document centred manner, i.e. the protocol is prepared 
for one application handling multiple documents (possibly even of 
different data-types). For controlling the object linking, use is made 
of a so-called OLGA-Manager (in short: Manager). Communication between 
the applications is transacted wholly via this Manager (which, by the 
way, can be present only once in the system).

The illustration below shows a simple model of OLGA communication.




The actual object linking is realized in OLGA with so-called links: 
these are references from the Client to data objects, or more exactly 
filenames with absolute path, which are saved by the Client in a 
document. If now the Server makes changes to an object for which a 
link exists, then the Client is informed of this (by the Manager), and 
can then update itself to display the updated object.

From Rev 1.2 (1996-11-20) onwards, extra functions were added and the 
OLGA architecture model now looks like this:




The above illustration shows the distribution of services between the 
OLGA-Manager and the applications using it (i.e. Client or Server). 
During linking, InplaceDrawing and Notification, the correct balance 
of communication between Manager and application for the embedding is 
the sole responsibility of the Client application.

Finally, the Info files are co-ordinated by the Manager but then 
operate directly between Server and Client applications. Schematically 
communcations are handled something like this:




See Also: AV protocol   Drag&Drop protocol