1. Experiences gained from enabling Interoperability in Aladin
Pierre Fernique [CDS]

2. Two interaction levels
Lower coupled level: a classical approach => command line parameters & files => http parameters & urls, => script commands (stdin or http) => widely open => heavily used
Highly coupled level: a java approach => java object interface => some implementations (VOPlot/AVO proto/CADC tools…)

3. The ExtApp context Connect VOPlot and Aladin:
Aladin asks VOPlot to create 2D diagrams
VOPlot asks Aladin to visualize astronomical data on the sky
Requires a management of the object selection callbacks (to select/highlight them in both applications)

4. 1. launch the other application 2. send objects 2. each application
can call the other one
to highlight or select
a list of objects

5. ExtApp.java
A symmetrical java interface implemented in both applications :
void loadVOTable(ExtApp app, InputStream in);
void showVOTableObject(String oid[]);
void selectVOTableObject(String oid[]);
String execCommand(String cmd);

6. Need for ExtApp2
To complete VOTable exchange: InputStream getVOTable(String dataSetID)
To exchange images : double [] getPixels(ra,dec,w,h) / (x,y,w,h) setPixels(x,y,pix[]) / (ra,dec,pix[])?
To allow observer registering : boolean add(this,MOUSE|PIXEL)
to transmit current mouse ra,dec position: void pos(ra, dec)
to transmit pixel under mouse position: void pix(double pix)

7. Lessons learnt Several solutions (depend on the interaction level)
Close interactions easy to implement inside java world…
But how to cross the java border? => PLASTIC