Apps Messaging - Semantics of a Message

[Doug Tody]

On Tue, 10 Apr 2007, Mike Fitzpatrick wrote:

> On 4/10/07, Mike Fitzpatrick <mjfitzpatrick at gmail.com> wrote:
>
> Just to clarify:  The whole point of this is to reduce the chance that
> Aladin, Mirage, DS9, XImtool, etc would all see fit to create their own
> mtype specific to the app.  They can still do this of course, but if
> display.whatever works for each of them the sender is free to use
> any of them without change.

Right.  This is a standard service/object model, with certain
operations ("display", "load", etc.), which is defined for a certain
type of data object ("image" in this case).  Nothing wrong with that,
and it is what is required for interoperable tools (components, apps,
whatever).  Of course it can be extended with tool-specific commands.

One interesting thing is doing this at a higher level of abstraction,
with a more limited set of high level, whole-object operations defined
(as in one of my earlier mails).  This simplifies the interface and
allows tools to directly manipulate the actual data objects, rather
than merely be told what to do by the client application.  The lower
level (or sometimes dual) XImtool/DS9 type of interface, where we can
do such things as load arbitrary data into frame buffers, is also
very powerful, but requires a much larger interface, significant
device state, etc.  Both approaches are worthwhile, and both have
their applications.

Even with a high level, whole-object interface, the client will need
to know what tool it is talking to, to be able to sequence a series
of requests.

 	- Doug