Annex J UDF on 120 mm DVD-RAM Medium (Normative)

This Annex defines the use of the UDF 1.5 file system with DVD-RAM media.

Notes: 1. Capitalization in this annex may be inconsistent with other DICOM standards in order to be consistent with historical usage for terms in referenced documents.

2. DVD-ROM is a pre-mastered medium, that is it is manufactured rather than written on a one-off basis by a medical device. While it is likely that a device conforming to this Annex will be able to read a UDF file system from DVD-ROM, it is not a requirement.

Universal Disk Format (UDF) version 1.5 is a profile of the ECMA 167 3rd edition file system.

Notes: 1. The ECMA 167 3rd edition is more recent than ISO 13346:1995 which is equivalent to ECMA 167 2nd edition.

2. Though later revisions of UDF such as 2.0 are defined with additional features compared to 1.5, these features are not required to support recording of a DICOM file set.

3. A reader of a UDF 2.0 file system can also read a 1.5 or 1.02 file system.

4. A UDF 1.02 reader cannot read the Virtual Allocation Table (VAT) used to incrementally write a UDF 1.5 or later disk.

5. A UDF 1.5 file system reader can theoretically read those structures of a UDF 2.0 file system that are common to both versions. However, a UDF 1.5 reader cannot read the Named Streams or extended file entries that may be recorded on a UDF 2.0 file system.

Since a UDF 1.5 reader may completely reject a 2.0 disk based on the version number written on the media, without attempting to read compatible structures of the file system, it is not permitted to write DICOM media with a version greater than 1.5.

6. A writer (FSC or FSU) is not permitted to add structures from a later version of UDF to a file system that has been created with an earlier version of the file system.

J.1 DICOM mapping to media format

J.1.1 Media Character Set

The character set used in UDF fields shall be the CS0 OSTA Compressed Unicode character set, required by the UDF standard.

Notes: 1. The CS0 OSTA Unicode character set is defined in UDF and is a subset of Unicode 2.0.

2. UDF defines a specific form of compression of 8 and 16 bit Unicode characters that must be supported.

2. The character set defined elsewhere in this section for DICOM File-set fields is a subset of this character set. However other fields in the UDF file system, and other files in the UDF file system not in the DICOM File-set, may use characters beyond those defined by DICOM for File ID Components, including those encoded in 16 bits.

J.1.2 DICOM File-set

One and only one DICOM File-set shall be stored on each side of a single piece of media.

A DICOM File-set is defined to be completely contained within one UDF File-set.

Only a single UDF File-set shall be present in the UDF Volume.

Each side of the media will comprise a single self-contained UDF Volume. That is the UDF Volume Set shall not consist of more than one UDF Volume.

Only a single UDF Partition shall be present on each side the media.

Note: Other partitions containing other file systems, possibly sharing the same data, may be present, such as an ISO-9660 bridge disk, a Mac HFS or Unix UFS hybrid disk, etc.

J.1.3 DICOM File ID Mapping

The UDF Standard provides a hierarchical structure for directories and files within directories. Each volume has a root directory that may contain references to both files and subdirectories. Subdirectories may contain reference to both files and other subdirectories.

J.1.3.1 File ID

PS 3.10 defines a DICOM File ID Component as a string of 8 characters from a subset of the G0 repertoire of ISO 8859. Each of these File ID Components is mapped to a UDF File Identifier or Path Component in the OSTA CS0 character set.

Note: This mapping is a subset of the MS-DOS mapping specified in UDF.

Filename extensions are not used in DICOM File ID Components, hence a UDF File Identifier shall not contain a File Extension or the '.' that would precede such a File Extension.

The maximum number of levels of a Resolved Pathname in a UDF file-set shall be at most 8 levels, to comply with the definition of a DICOM File-set in PS 3.10.

The File Version Number is always equal to 1, as specified by UDF.

Note: This file ID mapping is also compatible with ISO 9660 Level 1.

J.1.3.2 DICOMDIR File

A DICOMDIR file in a DICOM File-set shall reside in the root directory of the directory hierarchy, as specified in PS 3.10.

J.1.4 DICOM File Management Information

No file management information beyond that specified in the UDF File Entry is required. In particular no Extended Attributes or Named Streams are required.

J.2 FILESYSTEM

J.2.1 UDF File system

The reader shall be able to read a logical format conforming to UDF 1.02 or 1.5, as required by the UDF 1.5 standard.

The creator shall be able to create a logical format conforming to UDF 1.5.

The updater shall be able to update a logical format conforming to UDF 1.02 or 1.5, without updating the UDF revision level of the file system already recorded on the media, as required by the UDF 1.5 standard.

Options or extensions defined in UDF are required or restricted as specified in the following sub-sections, and in the media specific sub-sections.

J.2.1.1 Interchange Levels

For the UDF Primary Volume Descriptor, both the Interchange Level and Maximum Interchange Level shall always be set to 2.

Notes: 1. This means that the volume is not and will never be, part of a multi-volume set.

2. The Interchange Level and Maximum Interchange Level in the File Set Descriptor are defined by UDF to always be 3. This is despite the fact that restrictions specified for the DICOM File-set may be very similar to lower Interchange Levels specified in ECMA 167.

J.2.1.2 Virtual Partition Map and Allocation Tables

Creators and updaters shall not write UDF Virtual Partition Maps and Virtual Allocation Tables on DVD-RAM media.

J.2.1.3 Sparable Partition Maps and Sparing Tables

Creators and updaters shall not write UDF Sparable Partition Maps and Sparing Tables on DVD-RAM media, since defect management is performed in the drive.

J.2.1.4 System Dependent Requirements

The reader shall not depend on any system dependent requirements as specified in UDF to be able to read the DICOM File-set, and shall not behave differently if they are present. Any unrecognized system dependent requirements shall be gracefully ignored.

Notes: 1. For example, a particular form of file permissions, particular extended attributes or particular named streams may not be required or affect application behavior.

2. This does not mean that Extended Attributes or Named Streams may not be present and associated with files within the DICOM File-set.

J.2.1.5 Permissions and File Characteristics

Creators and updaters shall always create permissions for files within the DICOM File Set such that all users may read, write and delete all files, and all users may access and delete all directories on all systems.

Notes: 1. These requirements are equivalent to setting a Unix permission of 644 for files and 755 for directories.

2. The intent of these requirements is that for DICOM interchange media, implementation specific access control is not used or required.

The UDF File Identifier Descriptor for files within the DICOM File Set shall not specify a File Characteristic of "hidden.”

J.2.1.6 File Types

The UDF File Types within the DICOM File Set shall only be files (that is a File Type of 0, meaning unspecified interpretation) or symbolic links to files (that is a File Type of 12).

J.3 MEDIA FORMATS

J.3.1 DVD-RAM

J.3.1.1 DVD- RAM Physical Format

The physical format of DVD-RAM media shall comply with the applicable definitions within “DVD Specifications for Rewritable Disc (DVD-RAM 4.7GB): Part 1 - Physical Specifications Version 2.0” with the additional modifications described in the following sub-sections.

Note: Two physical forms of DVD-RAM are available, a double-sided variety (Type 1), and a single-sided variety (Type 2). Only Type 2 media can be removed from its cartridge and inserted in a conventional DVD-ROM drive.

J.3.1.1.1 DVD- RAM Sector Format

The sector format of DVD-RAM media shall comply with the applicable definitions in “DVD Specifications for Rewritable Disc (DVD-RAM 4.7GB): Part 2 - File System Specifications Version 2.0”.

DVD-RAM is a truly random access media, providing random access to fixed length sectors, hence no multi-session or packet-written format is applicable.

J.3.1.2 DVD- RAM Logical Format

There are no requirements, restrictions, options or extensions to the logical format that are specific to this media type, beyond those specified in section J.2.

J.3.1.3 DVD- RAM Physical Media

The physical medium shall be the 120 mm DVD-RAM medium as defined in “DVD Specifications for Rewritable Disc (DVD-RAM 4.7GB): Part 1 - Physical Specifications Version 2.0”.