One important concept in BDA is that of datatype. A datatype designation has been attributed to each kind of data. This designation is generally similar to acronyms currently used, like, for example: ubv, mk, uvby, jhk, and so on. The datatype designation is described in Appendix C.
The knowledge of the datatype is important because it is always used for querying the database. The datatype may be an argument to commands, like in list ubv, but more generally, many command names are identical to the datatype designation. For example, the command to get the UBV data for some stars, let's say star #1 2 3, will be simply: ubv 1 2 3.
This syntax and the fact that the data are collected in distinct files hide the name of the file that contains the desired data and the field names in each record.