Apps Messaging - Semantics of a Message

[Alasdair Allan]

Doug Tody wrote:
> I was thinking more in terms of a type of service, e.g., an image  
> or table viewer service/tool, registering with the "hub", after  
> which clients could expect it to perform some standard operations  
> defined for that type of client, or at least deal with certain  
> classes of data.  Hence Aladin would register as an image tool,  
> Topcat and VOPlot as table tools, VOSpec, SPLAT, Specview, etc. as  
> spectral analysis tools, and so forth.

Nooooooo! Why would you want to make that sort of arbitrary  
restriction? For instance Aladin can do interesting things with both  
tables and images (so can Topcat) but they do different interesting  
things.

> You seem to be suggesting instead that an application registers  
> that it can perform certain types of operations on certain types of  
> data, indicated via the mtype.

Yes, that's exactly how I think it should work.

> That could also work; I guess in this case one would be registering  
> the individual capabilities, expressed as
> the operations (indicated as mtypes) which the tool supports.

Yup, and it's a lot more flexible than the "image tool", "table tool"  
approach.

> Are we trying to define a standard service model for each major  
> class of astronomical data?

I really, really hope not. I think that's a doomed exercise.

Al.