In the current implementation of the `FileListDatabase`, there are functions generating and returning `Client`'s. The `Client` itself just stores the `client_id` and nothing else. Furthermore, the `Client` is used nowhere inside the biometric toolchain, only the `client_id` is used. I think, the `Client` class and according functions of the `FileListDatabase` were introduced for legacy purposes, i.e., to be comparable to other low-level databases. As we have decided to distinguish between low-level and high-level databases (and the `FileListDatabase` is a high-level database only, I don't think that we need the `Client` class here. Any opposition for removing those? They mess up the documentation here: https://www.idiap.ch/software/bob/docs/bob/bob.bio.base/master/implemented.html#bob.bio.base.database.Client by documenting a `Client` class in the middle of `BioFile`, `BioFileSet` and `FileListBioDatabase`...