The descriptive information associated with Bulk Data Frames (this is equivalent to the header of an IHAP file) is stored in a data structure called Descriptors in MIDAS. The concept is similar to the FITS header data (see reference ). Like keywords, descriptors consist of a name (max. 15 characters, case insensitive) and associated data values of any length (max. 32767) and of type `Integer', `Real', `Character', or `Double Precision'. The descriptor name may contain alpha-numeric characters and underscore. Descriptors are not global parameters, but are connected to a specific data frame. A minimum set of descriptors must exist for every data frame. These `Standard Descriptors' are explained in Appendix for Bulk Data Frames and Tables.