We are concerned with the extraction of tables from exchange format representations of very diverse composite documents. We put forward a flexible representation scheme for complex tables, based on a clear distinction between the physical layout of a table and its logical structure. Relying on this scheme, we develop a new method for the detection and the extraction of tables by an analysis of the graphic lines.To deal with tables that lack all or most of the graphic marks, one must focus on the regularities of the text elements alone. We propose such a method, based on a multi-level analysis of the layout of text components on a page. A general graph representation of the relative positions of blocks of text is exploited.