In the industry, there are various special formats of bulk data, that are non-structural data. Lacking of normal method to describe the structure of non-structural data, it is difficult to query and manage non-structural data as same as structural data. A architecture is put forward to describe the logical structure of bulk data, that is composite of three levels: the bulk data format definition language, special format definition, physical data file. Analyzed the components of bulk data file, the formal definition and the corresponding XML description are presented to define the logical structure of bulk data file. Considering the logical structure is dependent on the detailed data in bulk data file, an format definition language is defined in XML schema, that can define difference kinds of bulk data format. To access data by logical structure for bulk data file, the approach of mapping from logical structure to physical file is presented. Above method has been applied to manage seismic data in petroleum domain.