particle system

Personally, I would structure it like this:

Each particle as an individual object, hence with it''s own behaviour etc.
The system is then an object that controls a collection of particles.

So to answer your question, the behaviour of particles would be determined by each individual particle [its render method]. That way, you can have particles with different life spans and such to each other. I would say basic attributes for particles are:
- Lifespan
- Colour
- Weight (not always necessary)
- Direction (velocity can be stored here too)
- Position

The system should be responsible for:

Spawning the particles at a given point and giving the particle a direction and speed (which is stored in the particle itself) and ensuring there are always the right number of particles onscreen [hence the system would contain an array of particles or pointers to particles]. so when you want to relocate the place where the partciles spwan, you move the system...
so attributes:
- position
- direction (one direction, out in all directions - so could call it expulsion type)
- max number of particles
- explusion speed
- max number of particles

and also a method for rendering all relevant particles (or calling each particles render function)

hope that helps. I am sure there''s more to contribute though..

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