Wash eggplant. Do not peel, Cut into 3 cm cubes. Season with salt and pepper. Fry in heated oil until tender. Take out and set aside. Saute onion in the same oil until tender. Add garlic, celery, tomatoes, and olives. Cook slowly for 10 minutes. Add eggplant, pine nuts and capers. Heat vinegar and stir in sugar. Add to vegetable mixture. Season with salt and pepper. Cook for 5 minutes longer. Serve chilled as an appetizer or relish.