C.I.E – Carta di Identità Elettronica Functional Specification Version 2.0

10. Data StructuresThe CIE holds data either in files, or in objects. The difference between them lies in the logicalorganization and in the access mode.Files are organized in a file system, organized in a hierarchical tree structure.To access a file, it has to be selected (either implicitly or explicitly), and has then to become thecurrent file.Objects are referenced implicitly or explicitly by dedicated commands, do not need to be selected(actually they cannot be selected with a Select command).Some implementation may actually map objects onto internal files, that will be allocated in the filesystem, but nevertheless the access rules for those objects remain the same.File system organization, coding and access are regulated by [2], as described in the followingchapters.10.1 File CategoriesThe CIE file system is based on three categories of basic file components:The root of the file system, the Master File (MF),Directory files, denoted as dedicated files (DF),Generic data files, denoted as Elementary files (EF).The Master File (MF) is the root of the file system and is always the initial entry point to the filesystem. After a reset of the card, the MF is selected.The Dedicated Files (DFs) are similar to Directories in traditional file systems.DFs can contain Elementary Files (EFs), and/or other DFs. The MF can be considered to be aspecial DF that contains all the files.The Elementary File (EF) is used for data storage. For this reason EFs are also referred to as datafiles. File access is similar to traditional file systems. To access a file (for reading, writing, or anyother operation), it has to be selected.10.2 Data File TypesThe following structures of EF are defined:Transparent structure:The EF is seen at the interface as a sequence of bytes.CIE - Functional Specification v 2.0 -Page 22/76