Learning a new data format - read the specification or read the DFDL schema?

[Roger L Costello <co...@mitre.org>]

Hi Folks,

I am learning the NITF (image) data format. I downloaded both the NITF specification and the DFDL schema. To learn NITF, should I read the specification or read the DFDL schema?

I chose to read the DFDL schema first. I'm glad I did because it has given me a nice high level view of the data format.

Here's what I learned: NITF starts with a header section containing metadata about the entire file. Following that are a series of segments. Each segment contains a header followed by data. The first segment is the image segment. In it you can plug in a JFIF image or a JPEG2000 image or other types of images. There can be 0-999 image segments. Following those segments is 0-999 graphic segments. The DFDL schema treats its data simply as a bunch of hex digits. Following them is 0-999 text segments. The DFDL schema treats its data simply as a long string. Next is 0-999 data extension segments followed by 0-999 reserved extension segments. The DFDL schema treats their data as a bunch of hex digits. Here's a graphic showing the structure of NITF files:

[cid:image001.png@01D7DA1A.20FA5300]

Of course, to get a fuller understanding of the meaning of these segments, I will need to read the specification.

/Roger