On 11/17/2017 08:05 AM, Mike Beckerle wrote: > This is lower priority than many things, but a while back we tried to create > a DFDL schema for TIFF and failed. > > > DFDL features for base+offset location of elements never were designed. They > were dropped in the haste to get DFDL v1.0 finished. > > > But I happened to ask Dave Sugar of the Tresys CADRE team whether the CADRE > engine (a binary data format description - for wire-speed applications) could > do TIFF? Turns out some work was done on this, and I was able to look at the > format specification for TIFF (a prototype thereof for CADRE). > > > So the features for DFDL to suppport base + offset locations don't seem too > daunting. > > > I created a wiki page to capture the design ideas here. There's more work to > do on this. We really should write the DFDL schema for TIFF using these > features to be sure we're happy with it. Thus far I've not taken the time to > do that. I've just recorded the basic ideas. > > > https://cwiki.apache.org/confluence/pages/viewpage.action?pageId=74687382 > >
You specify a requirement that dfdl:offset be non-negative--could that be too restrictive? For example, I could imagine a (really dumb) file format where it essentially chains blobs together, with the position of the next blob relative to this one, e.g.: 0: Blob-1, Next: +5 1: 2: Blob-4, Next: +2 3: Blob-3, Next: -1 4: Blob-5, End 5: Blob-2, Next: -2 I'm not sure supporting a format like this would be possible without negative offsets. If no format has something like this I'm not sure it matters and restricting to non-negative is completely reasonable, but I thought you could do something like this with TIFF? Maybe not? - Steve
