The projected, numerical factual database BEILSTEIN-ONLINE represents a natural extension of the Beilstein Handbook of Organic Chemistry which has been published for more than 100 years in more than 300 volumes. The Handbook together with the structure file cards of the literature period 1960–1980 (E-V Period) contain factual and structural information on more than 4 million compounds. The computer representation of organic chemical structures therefore constitutes the centre part of the database design. The chemical structure is described in a post-topological format. Not only constitutional information is included but also a complete stereochemical representation. Bond orders are replaced by electronic information. This allows a much more global and unique representation of tautomers. This paper gives an overview not only of the data structure of chemical compounds but also of its associated physical numerical data and keywords.