natanael.arndt.xyz

@white_gecko at 2025-11-17 15.50

Mon, 17 Nov 2025 15:50:00 +0100

At the 17th Semantic Web in Libraries Conference (SWIB2025) Tracy gave a talk about our joint work on describing the web archives collection as linekd data How to describe the past Web? A data model for web archiving by Tracy Arndt and Natanael Arndt (Slides).

Convert a Presentation to a Video

Fri, 20 Jun 2025 15:46:00 +0200

At some event we had a screen to show some slides, as well as a pre-produced video, to summarize our project outcomes. Since my presentation tool-chain mostly involves LaTeX beamer slides, I came up with the following script to convert the PDF pages into video frames and concatenate another video file.

#!/bin/sh

convert -density 609 -resize 1920x1080 main.pdf video/picture.png
cd video
ffmpeg -r 1/6 -i picture-%01d.png -c:v libx264 -r 30 video.mp4
ffmpeg -i video.mp4 -i second_video.mp4 -f lavfi -t 1 -i anullsrc -filter_complex "[0:v][2:a] [1:v] [1:a] concat=n=2:v=1:a=1 [v] [a]" -map "[v]" -map "[a]" out.mkv

The inputs are:

main.pdf with your slides
video/second_video.mp4 with the video you want to attach

The output will be at video/out.mkv.

The slides should be in 16:9 format, so that it nicely scales to 1920x1080 (Full-HD). All other options should be documented at https://ffmpeg.org/.

@white_gecko at 2025-04-09 11.55

Wed, 09 Apr 2025 11:55:00 +0200

Talk: IIPC WAC - Under Construction: Web Archive of the German National Library by Natanael Arndt (Video)

@white_gecko at 2024-11-19 19.30

Tue, 19 Nov 2024 19:30:00 +0100

Talk: ISKO UK Meetup - Introducing Jekyll RDF by Natanael Arndt

@white_gecko at 2024-04-18 15.00

Thu, 18 Apr 2024 15:00:00 +0200

Talk at the 12th Leipzig Semantic Web Day (LSWT2024) co located with the Data Week Leipzig 2024 - The Web Archive of the Future at the German National Library (Das Webarchiv der Zukunft an der Deutschen Nationalbibliothek) (Slides; Video)

Cherry pick files from a commit in a repository

Fri, 01 Mar 2024 14:13:00 +0100

In git there is the command git cherry-pick that allows to “apply the changes introduced by some existing commits”. This is nice if you want to reorder entire commits or things like that.

I often have the use case that I want to see individual files side-by-side to compare them or overwrite files with a previous version, your might have more precise use cases in mind. At the beginning I thought git cherry-pick is the command I was looking for but I sound found out, it is not. So I went back, often to the GitHub web interface and just browsed the history and then the file tree to view the file at a certain state.

But since git has a very nice object storage I found out, that I can get any object with git show ${object_id} resp. git show --format=raw ${object_id}. An object can be a commit, a tree (directory), or a blob (file). So I needed to get the object id of the blob that I want to see. This can be done with git ls-tree command resp. to just get the specific id of the file I’m looking for: git ls-tree --object-only -r ${commit} ${file}.

All to gather I have put this into these lines, which you can find at https://github.com/white-gecko/git-cherry-file:

#!/bin/sh
## Done by Natanael 2023-01-31
# see also: https://stackoverflow.com/a/42623347/414075
commit=$1
file=$2
target_file=${3:-${file}.cherry}
echo "Pick ${file} from commit ${commit}"
file_id=$( git ls-tree --object-only -r ${commit} ${file} )
echo "It has the object id ${file_id}"
git show --format=raw ${file_id} > ${target_file}
echo "Written to ${target_file}"

Just make it executable and put it into your path, e.g. ~/.local/bin/git-cherry-file and call it with:

$ git-cherry-file HEAD~2 README.md

It will create a new file README.md.cherry. If you want to specify the target path you can add it as an additional argument, e.g. to overwrite the current file:

$ git-cherry-file HEAD~2 README.md README.md

I hope you like it.

Animate the History of your Git Repository

Sat, 13 Nov 2021 17:54:00 +0100

I was looking for a way to get an impression of the temporal development of my git repository. So I chose to check for ways to animate the history of a git repository.

I found some DIY approach that should provide very nice results, but it requires some more effort. Basically you iterate through all of your commits, execute a command to visualize this commit, what ever that means to you, and then merge all of these visualizations as frames together as a movie file. The exect steps are here: http://eptcomic.com/ept1movie.htm.

Another tool is Gource (https://gource.io/). It renders your repository in a 3D animation, that looks quite fancy. A good startingpoint is:

$ apt install gource
$ gource -c 4.0 -s 1 -a 1 .

The major difference between the two tools and their results is, that with the first on you can visualize the content of the repository as it evolves, while the Gource mainly visualizes the file structure and the collaboration process on it.

(This post was originally started on 2020-10-18)

Backup done right … and what about config?

Wed, 23 Dec 2020 20:01:00 +0100

From time to time it is important to create a backup of your data. There are some tools that help one to copy files in some sophisticated ways onto a different medium. I chose restic for this job.

But this only works well for the data you are working on, we call it user data, but not for your configuration. Some backup articles suggest to just backup the complete users home directory which stores the user configuration, but this will not include the system configuration. On top of this for me a backup is not a raw copy of the current system I’m working on, but just the actually relevant data and configuration. This can also come along with an additional use case for a backup, that I want to use it to setup a clean new system where I only want to take over the data that I actually need.

So far I have not found any system, that covers the aspects mentioned, which leads me to the point that I’ve started to write down a concept for a configuration backup system. You are welcome to send any hints and suggestions.

Dissertation: “Distributed Collaboration on Versioned Decentralized RDF Knowledge Bases”

Tue, 15 Dec 2020 13:07:00 +0100

If you are looking for a good read for the holiday season or even a geeky present check this out. My dissertation “Distributed Collaboration on Versioned Decentralized RDF Knowledge Bases” is now published at the Open Access University Press Leipzig (Open-Access-Hochschulverlag Leipzig) which is situated at the Leipzig University of Applied Sciences (HTWK Leipzig). It is available online as Open Access (DOI 10.33968/9783966270205-00) and at your favorite book shop (isbn: 978-3-96627-019-9).

The book comes along with a preface by by supervisor Prof. Dr. Thomas Riechert and my reviewer Prof. Dr. Cesare Pautasso. The book cover is a design from Annett Riechert a local designer from Leipzig (her blog post). The epub version is still in production. The book is the first volume in the new series “Publikationen in der Informatik” (Publications in Computer Science), expect more to come …

You can find the abstract as well as the full text in the according entry in my publication list.

@white_gecko at 2020-10-14 18.05

Wed, 14 Oct 2020 18:05:00 +0200

If you are doing #SoftwareDevelopment resp. #SoftwareEngineering an looking for a #LaTeX/#TikZ version of a simple agile development #cycle check out my page ;-) https://natanael.arndt.xyz/notes/agile #SCRUM #agile

@white_gecko at 2019-11-19 12.52

Tue, 19 Nov 2019 12:52:00 +0100

If you want to read my papers but you are to lazy to download them and open them with your favorite PDF reader you now get the service to read them all directly on my web page. Some as #HTML some as embedded #PDF. https://natanael.arndt.xyz/publications #OpenResearch #OpenAccess

@white_gecko at 2019-08-06 17.03

Tue, 06 Aug 2019 17:03:00 +0200

If you are working on #SemanticWeb an looking for a #LaTeX/#TikZ version of the #LayerCake and the #LODCycle check out my page ;-) https://natanael.arndt.xyz/notes/semantic-web-layer-cake and https://natanael.arndt.xyz/notes/lod-cycle #LOD

@white_gecko at 2018-11-27 18.26

Tue, 27 Nov 2018 18:26:00 +0100

Just released #JekyllRDF 3.1.0! The cool new feature is that you can now build pages from a #SPARQL endpoint. Checkout the CHANGELOG and README for details. We hope you like it. https://rubygems.org/gems/jekyll-rdf https://github.com/white-gecko/jekyll-rdf @akswgroup (https://mobile.twitter.com/white_gecko/status/1067452594954661889)

@white_gecko at 2018-10-20 19.26

Sat, 20 Oct 2018 19:26:00 +0200

Now you can find my paper “A Method for Distributed and Collaborative Curation of RDF Datasets Utilizing the Quit Stack” 10.18420/in2017_187 with the full text published as HTML and #OpenAccess #OpenResearch on my #JekyllRDF blog https://natanael.arndt.xyz/bib/arndt-n-2017–quitstack

My Bibliography with Jekyll RDF

Wed, 10 Oct 2018 15:10:00 +0200

From now on the list of my publications is rendered using Jekyll-RDF. I’ve used the bibtex2rdf script together with a customized mapping to convert my bibtex file to RDF. This file is consumed by JekyllRDF and rendered together with the rest of my blog using the publications template for the lost of all publications and an additional template to render a page for each individual publication resource.

Jekyll RDF Tutorial Screencast

Tue, 07 Aug 2018 10:13:00 +0200

Today I’ve released my #jekyllrdf Tutorial Screencast on Vimeo. It teaches you all the basics necessary to create a simple Jekyll page from an RDF knowledgebase. I hope that you enjoy it and that it is helpful for you!

Generate a QR Code to Recover Your OTP Secret

Tue, 27 Feb 2018 13:18:00 +0100

Bitcoin.de as some other pages is using a One-Time-Pad (OTP) as two-factor authentication method, actually it is a Time-based One-Time Password algorithm (TOTP). The Passwords are generated based on a shared secret as specified in RFC6238. When activating the two-factor authentication on bitcoin.de the page shows a QR code which is used by OTP apps, such as andOTP (github), Google Authenticator, or OTP Authenticator (github), to transfer the shared secret to the phone. Additionally the page shows the shared secret as a string of letters and numbers, which one should write down and deposit in a safe place.

But what happens, if due to some circumstances you have to bring this shared secret back into the app? The google app provides the possibility to manually enter the string of letters and numbers, but the other two apps don’t. Thus it is necessary to generate a QR code which encodes the shared secret. Unfortunately I didn’t find a comprehensive guide how to do this but I found some pieces, which I had to put together. The first pieces was in the LinOTP documentation which told me that the QR code actually just encodes a URI, but the example was not TOTP. After some more web search I found a python script, which generates all sorts of OATH URIs. Now I know, that the syntax of the URI actually is:

otpauth://totp/<name>?secret=<secret>

As we know already we can use qrencode to generate QR codes (see also this post about WiFi access QR-codes):

qrencode -o code.png -t png "otpauth://totp/<name>?secret=<secret>"

Now just open code.png with an image viewer on your PC and scan the code with your phone.

Some more stuff which I found during my web search:

https://blogs.forgerock.org/petermajor/2014/02/one-time-passwords-hotp-and-totp/
http://www.nongnu.org/oath-toolkit/

@white_gecko at 2018-01-02 14.03

Tue, 02 Jan 2018 14:03:00 +0100

Ein neues Rezept ist online: Kartoffelsalat mit Räuchertofu.

@white_gecko at 2017-11-04 18.44

Sat, 04 Nov 2017 18:44:00 +0100

Now I’m able to write status posts from my mobile using #FastHub-Libre :nerd:

@white_gecko at 2017-10-23 15.51

Mon, 23 Oct 2017 15:51:00 +0200

Today we’ve released #jekyllrdf 2.3.0 at #rubygems https://rubygems.org/gems/jekyll-rdf, read more: https://natanael.arndt.xyz/2017/10/23/jekyll-rdf-2.3.0 #ruby #jekyllrb

https://twitter.com/white_gecko/status/922460422095196166