Use kgdiff with git

Compare two revisions

Pipe one side from git show. - reads it from standard input, and the format is detected from the content:

git show main:ontology/onto.ttl | kgdiff - ontology/onto.ttl

To compare two older revisions, or to open the report, write them to files. Keeping the extension keeps format detection simple:

git show v1.0:onto.owl > /tmp/onto-v1.0.owl
git show v2.0:onto.owl > /tmp/onto-v2.0.owl
kgdiff /tmp/onto-v1.0.owl /tmp/onto-v2.0.owl -o report.html --open

git difftool

Register kgdiff once:

git config --global difftool.kgdiff.cmd 'kgdiff --title "$MERGED" "$LOCAL" "$REMOTE"'

and use it for graph files:

git difftool --tool=kgdiff --no-prompt main -- ontology/onto.ttl

git writes the old version to a temporary file that keeps the original file name, so formats are detected as usual, and $MERGED puts the path in the title. To open the interactive report instead of printing the summary, register a second tool:

git config --global difftool.kgdiff-report.cmd \
  'kgdiff --title "$MERGED" "$LOCAL" "$REMOTE" --open -q'

--open without -o writes the report to a new temporary directory and opens it.

git diff, git show and git log -p

To have git diff itself use kgdiff for graph files, declare a diff driver. Mark the files in .gitattributes:

*.ttl diff=kgdiff
*.obo diff=kgdiff
*.owl diff=kgdiff

and define the driver, in .git/config for one repository or in ~/.gitconfig for all of them:

[diff "kgdiff"]
	command = sh -c 'kgdiff --allow-empty --title \"$0\" \"$1\" \"$4\"'

git calls the command with seven arguments (path, old file, old hash, old mode, new file, new hash, new mode), which sh -c sees as $0 to $6: kgdiff compares the old and the new file and uses the path as the title. --allow-empty compares an added or deleted file with an empty graph, since git passes /dev/null for the missing side.

Now git diff shows kgdiff's summary for those files:

$ git diff -- vocab.ttl
kgdiff  vocab.ttl                                        66 → 71 nodes · 105 → 112 edges

  +3 added   ~6 modified   ⇄5 restructured                        27 changes in 14 hunks
  …

• git log -p and git show use diff drivers only with --ext-diff; git diff --no-ext-diff shows the text diff again.
• Output going to git's pager is not a terminal, so kgdiff prints it without color. Add --color=always to the command if your pager shows ANSI colors, as git's default less -R does.

Merging

kgdiff compares two versions; it does not merge three. Keep git's default merge for graph files. Three-way merge with conflict visualization is on the roadmap.