STANDARDS CHANGE REQUEST - Upper/Lower Case Standards ===================================================== Purpose: Establish rules on the use of upper/lower case characters in file and directory names -- first in a media independent manner, then as used when writing DVD archive volumes. CD (CD-ROM or CD-R) archive volumes will continue to be written according to the current standards. Date: February 11, 2005: revision 4.0 Note: Name changed from DVD Case Standards to Upper/Lower Case Standards Working Group: J. Wilf (lead), C. Isbell, C. Atkins, M. McAuley, T. King, E. Means and L. Huber Background ========== When Chapter 19 of the PDS Standards, "Volume Organization and Naming," was written, it was intended specifically for archive volumes written to compact optical disc (CD) media. It therefore followed the ISO-9660 standard, which specifies the file and volume structure for CD media and requires UPPER CASE directory and file names. As PDS data volume grew, it became necessary to archive on higher-capacity DVD media. The Data Distribution Laboratory (DDL), which had helped develop the PDS standards for CD media volumes, made the following recommendations for DVD. These were based on extensive media testing, with the purpose of ensuring the most uniform ability to read and write DVD media across all computer platforms: 1) Write DVD media using the UDF-ISO9660 bridge format, where UDF (Universal Disk Format) is a filesystem standard chosen for DVD and higher-capacity media, and where the UDF-ISO bridge format creates both an ISO-9660 and UDF partition on the DVD. 2) Convert all directory and file names to lower case before writing the DVD. This leads to a lower case UDF partition and an upper case ISO-9660 partition, since the DVD-writing software automatically does lower-to-UPPER case conversion for the ISO-9660 partition. Case is preserved within the UDF partition. Although the UDF partition can accept either upper or lower case names, there were several reasons for choosing lower case. DDL testing showed that the lower case UDF partition was read correctly across Windows, Solaris, Linux, and Mac platforms, whereas an upper case UDF partition was read incorrectly on Windows as having an upper case first character, followed by lower case subsequent characters. Also, user interface studies have shown that lower case directory and file names are far more readable. The problem is that the recommendation described above conflicts with the PDS Standards Reference, which always specifies upper case names for files and directories. Data providers are understandably confused when they see upper case names in the Standards but are told to create lower case names on DVD. More importantly, it is recognized that the archive should be as independent as possible from the media on which it is currently stored. CD media are already giving way to DVD. Plans are in place to move responsibility for long-term archiving to the NSSDC, where "archive packages" will be stored on the media of NSSDC choice -- and refreshed and migrated to new media as needed. In this environment, it is important to have a file/directory standard that is media independent. And therefore, this SCR establishes a media independent file/directory standard on the use of upper/lower case filenames first, then describes the standards that apply when writing these files to DVD media. NOTE: Recommendations for specific hardware, software, software settings, and media for writing to DVD media will be given in a separate document, rather than the Standards Reference. Current Urgency =============== The MGS-Extended and NEAR missions have already delivered archive data on DVD media, and the Cassini mission is planning to do so in the near future. Upper/lower case issues must be resolved for these deliveries. Recommendations =============== Given the urgency described above, the PDS Project Engineer recommends the following actions: 1. To Management Council: Approve the UPPER/LOWER CASE SCR as soon as possible. 2. To the PDS Standards Lead: Upon Management Council approval, publish the changes in the next version of the PDS Standards Reference, as described in the paragraphs below. Changes to the Standards Reference - Overview ============================================= Upper/lower case requirements for all file and directory names -------------------------------------------------------------- All file and directory names within the same data set archive must have the same case. The data provider may choose either upper case or lower case, but once the choice is made, that case must be used consistently for every file and directory in the data set archive. Software files that require mixed-case names must be distributed within a correctly named ZIP archive. For example, HelloWorld.class, a Java class file for the class HelloWorld, might be contained in helloworld.zip. Upper/lower case requirements for file names used in PDS labels --------------------------------------------------------------- File and directory names used in PDS labels, e.g., as a pointer to a file on disk, may be either upper or lower case. (It is recommended that the file name in the label match the case of the actual file name, but this is a guideline, not part of the standards.) NOTE: Values for ODL identifiers that may use file name information, e.g., VOLUME_ID, will remain upper case. Upper/lower case requirements for file names in PDS index tables ---------------------------------------------------------------- File and directory names used in PDS index tables may be either upper or lower case. (It is recommended that the file name in the index table match the case of the actual file name, but this is a guideline, not part of the standards.) Upper/lower case requirements for archive and transfer media ------------------------------------------------------------ Media used to archive or transfer PDS data set archives must support the upper/lower case choice made for that data set archive. For example, if a data provider chooses to archive in lower case, then CD media cannot be used, since PDS requires CD volumes to comply with the ISO9660 standard, which accepts only upper case names. Data providers choosing to archive in lower case may currently write DVD volumes using the UDF-ISO9660 bridge format. Changes to the Standards Reference - Specifics ============================================== Section 1.6: Add reference to UDF-ISO9660 bridge format. Section 5.1.2: Change "All values in a PDS label should be in upper case, except values for descriptive elements (DESCRIPTION, NOTE, etc.)" to include pointers and file specification names. Section 5.3.3: Add a lower case example, i.e., ^TABLE = "data.dat" Section 5.3.3.2: Item (b) in the list, "file names must be in upper case" should be changed to "file names may be in either upper or lower case." The examples should also be changed. Section 8: In the introduction, alert the user that although upper case examples are given, the case may be upper or lower, as long as it is consistent within a data set archive. Section 8.2: Item (1) in the list, "A directory name must consist of only uppercase aphanumeric characters and the underscore character" should be changed to reflect that upper or lower case characters may be used, but no mixed case, and case should be consistent across the data set archive. Section 8.3: Add the option of lower case path names to the description of path specification. Section 10.2: Indicate that both upper and lower case versions of the reserved directory and file names are reserved. Chapter 11: Indicate that the media chosen by the data provider must support their choice of upper or lower filenames. CD media cannot be chosen for lower case filenames. Chapter 14: Add text and examples explaining recomendataion for case consistency between pointer value and file name. Chapter 19: Add that directory and filename examples are given in upper case, but may be in lower case, depending on the case chosen for the data set archive. Also note again that the media chosen by the data provider must support their choice of upper or lower filenames. CD media cannot be chosen for lower case filenames. Appendix A.21.4.1: Add that it is recommended that FILE_SPEC_NAME or PATH_NAME plus FILE_NAME should match the case chosen for the dataset archive but not required. Changes to the Data Dictionary - None ============================== Changes to the PDS Tool Suite ============================= All Common PDS Tools will be modified, if needed, in order to access PDS files in a case insensitive manner. Changes to the PDS Online System ================================ All Online System software that accesses PDS data repositories will be modified, if needed, in order to access PDS files in a case insensitive manner. Impact Statement - TBD ================ [Changes to the tools and system remain to be analyzed] Open Issues =========== * Analysis for impact statement [END OF SCR]