Time‐travel with PRONOM: The 4th dimension of DROID Michelle Lindlar, Yvonne Tunnat TIB German National Library of Science and Technology, ZBW Leibniz Information Centre for Economics Research Question: How stable has file format identification for PDF, JPEG (JFIF), GIF and TIFF been across the past 18 years of PRONOM / DROID signature patterns? Scope: Limited to signature patterns (excluding impact of DROID engine changes) and limited to subset of file formats for each family. All signature patterns used for time machine analysis. PRONOM release notes analysis was restricted to the available release notes (v31‐v93). Approach: Experiment with “Time Machine” which runs through all signature patterns; release note analysis. Background and Motivation TIB and ZBW are both actively involved in digital preservation, working collaboratively in a digital archive with > 1.7 million files. Knowledge of a digital object’s file format is the basis of our functional preservation planning and action. But how can we verify this knowledge? And how reliable is the outcome of standard processes using DROID and PRONOM? Does automatically identified file format knowledge have persistence in itself – both from a PUID as well as from a ground truth point of view? Research Question and Approach PRONOM release signature timeline Google Test Suite TIFF, GIF and JPEG. Available at: https://code.google.com/archive/p/imagetestsuite/downloads Govdocs Testsuite. Digital Corpora Website. Available at: http://digitalcorpora.org/ ISO 32000‐1:2008. Document management – Portable document format – Part 1: PDF1.7. https://www.iso.org/standard/51502.html ISO 19005‐1:2005. (PDF/A‐1). https://www.iso.org/standard/38920.html : PRONOM/DROID Release Noes. The National Archives. Available at: http://www.nationalarchives.gov.uk/aboutapps/pronom/release‐notes.xml TIFF Revision 5.0. Aldus/Microsoft Technical Memorandum. Available at: http://cool.conservation‐us.org/bytopic/imaging/std/tiff5.html Sherlock Carriage – PRONOM’s blind spot on (some) PDFs from 2010 to 2014. Yvonne Tunnat. Available at: http://openpreservation.org/blog/2018/07/25/sherlock‐carriage‐pronoms‐blind‐ spot‐on‐some‐pdfs‐from‐2010‐to‐2014/ References What has happened to PDF‐identification between 2010 and 2014? How persistent were the first TIFF‐PUIDs? Was a JPEG always a JPEG and a GIF always a GIF? How did we find all of this out? Discussion and Conclusion Want to know more? Click arrows for answers How stable has file format identification for PDF, JPEG (JFIF), GIF and TIFF been? All files had identification problems in the early stages of PRONOM and could not be identified with patterns V1‐4. From there on, results differed by file format family. JPEG (JFIF) and GIF identification remained stable throughout all other versions. However, a closer analysis of the release notes showed that both patterns changed over the course of time. While JPEG raised the offset of the End of File marker three times, allowing for up to 65536 bytes after the EOF marker, the gif pattern was only changed once, allowing up to 4 bytes of data after the EOF pattern match. While the test corpus identification outcome was not affected by this, files within an archive might very well be impacted by these changes to JPEG and GIF patterns. PDF pattern changes were more frequent, leading to drastic results, such as the „dark age of (some) PDFs“ between 2010 and 2014. For „plain PDF“, i.e. PDF 1.0‐1.7, identification has been fairly stable since V77 (Oct 2014), while changes still occur regularly to PDF profile formats such as the PDF/A or PDF/X formats. A PUID and pattern for PDF2.0 (fmt/1129) was released in V93. The pattern will have to be observed closely, as first writers for PDF2.0 are currently being developed. Impact on identification workflows In functional digital preservation many processes – such as risk assessment and preservation planning but also rendering paths ‐ are based on knowledge about a digital object’s fil