Block-diagram libraries?

[Emanuele <sarbyn gmail com>]

I need to develop an application that dump a config file (an ASCII file) 
for a simulation framework.
The user drag & drop the component (cpu, memory, comunication channel, 
etc) from a library into a "work-area" and link the component (like a 
Dia diagram).

Are there any library that semplify the drawing of the diagram (link two 
entity of the diagram with a line, move the component and the links on 
the work-area, etc etc)?
Or must I implements all the grafical routines?

Thanks

--
Emanuele

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