1. A data processing network for which a plurality of product selling enterprises, a plurality of product planning and selling enterprises, a plurality of product processing and manufacturing enterprises and a plurality of material selling enterprises subscribe, comprising: a database for gathering and accumulating data retained separately by said plurality of product selling enterprises for independently selling products, by said plurality of product planning and selling enterprises for independently planning and selling said products, by said plurality of product processing and manufacturing enterprises for independently processing and manufacturing said products and by said plurality of material selling enterprises for independently planning, manufacturing and selling materials of said products; a plurality of first terminals, provided in each of said plurality of product selling enterprises, for: inputting business history data on products to be actually sold, inputting one of retrieval instructions as to the business history data, data on manufacturing and selling said products and data on products in stock, sending the input data and retrieval instructions, receiving retrieved business history data, data on manufacturing and selling said products and data on products in stock, and outputting the received data; a plurality of second terminals, provided in each of the plurality of product planning and selling enterprises, for: inputting said business history data on products to be actually sold, said data on manufacturing and selling said products and said data on products in stock, inputting one of retrieval instructions as to data for use in planning the products, data for use in planning the materials, data on manufacturing and selling the products to be actually sold, the data on products in stock, data on the materials in stock, business history data on the products and business history data on the materials, sending the input data and the retrieval instructions, receiving retrieved data for use in planning the products, data for use in planning the materials, data on manufacturing and selling products to be actually sold, data on products in stock, data on materials in stock, business history data on the products and business history data on the materials and outputting the received data; a plurality of third terminals, provided in each of said plurality of product processing and manufacturing enterprises, for: inputting retrieval instructions as to the data on manufacturing and selling the products to be actually sold, sending the input retrieval instructions, receiving retrieved data on manufacturing and selling the products to be actually sold and outputting the received data; a plurality of fourth terminals, provided in each of said plurality of material selling enterprises, for: inputting data on manufacturing materials to be used as goods, the data on materials in stock, the business history data on the materials, inputting one of retrieval instructions as to the data for use in planning the products, the data for use in planning the materials, the data on manufacturing materials to be used as goods, the data on materials in stock and the business history data on the materials, sending the input data and the retrieval instructions, receiving retrieved data for use in planning the products, data for use in planning the materials, data on manufacturing materials to be used as goods, data on materials in stock and business history data on the materials, and outputting the received data; and control means, connected to said database and connected to said plurality of first to fourth terminals through a communication line, for: storing data sent from said first to fourth terminals, and retrieving data instructed by said database in accordance with the retrieval instructions sent from one of said first to fourth terminals; and said database including: a plan data database for storing at least the data for use in planning the products and the data for use in planning the materials; a product database for storing at least data on producing and selling the products to be actually sold and data on products in stock; a material database for storing at least the data on manufacturing the materials to be used as goods, and the data on materials in stock; and a business history database for storing at least the business history data on the products and the business history data on the materials.