diff --git a/docs/01-basics/LG-01-07.adoc b/docs/01-basics/LG-01-07.adoc
index 22a2375..6d135f5 100644
--- a/docs/01-basics/LG-01-07.adoc
+++ b/docs/01-basics/LG-01-07.adoc
@@ -30,4 +30,4 @@ They
 // end::EN[]
 
 ===== {references}
-<<felleisenetal>>, <<sperberklaeren>>, <<kleppmann>>, <<fordhardparts>>
+<<felleisenetal>>, <<sperberklaeren>>, <<sperberwehr>>, <<kleppmann>>, <<fordhardparts>>
diff --git a/docs/09-references/00-references.adoc b/docs/09-references/00-references.adoc
index 3c5f6dd..78de5c7 100644
--- a/docs/09-references/00-references.adoc
+++ b/docs/09-references/00-references.adoc
@@ -105,6 +105,7 @@
 // S
 - [[[solid, SOLID]]] Samuel Oloruntoba and Anish Singh Walia: SOLID: The First 5 Principles of Object Oriented Design, <https://www.digitalocean.com/community/conceptual-articles/s-o-l-i-d-the-first-five-principles-of-object-oriented-design>.
 - [[[sperberklaeren, Sperber+2023]]] Michael Sperber, Herber  Klaeren: Schreibe Dein Programm!  Tübingen University Press, 2023.  <https://www.deinprogramm.de/sdp/>.
+- [[[sperberwehr, Sperber+2024]]] Michael Sperber, Stefan Wehr: Datenmodellierung mit Summen und Produkten, 2024.  <https://funktionale-programmierung.de/2024/11/25/sums-products.html>. (English translation: Data Modeling with Sums and Products, 2024. <https://funktionale-programmierung.de/2024/11/25/sums-products-english.html>)
 - [[[starke,Starke 2024]]] Gernot Starke: Effektive Softwarearchitekturen - Ein praktischer Leitfaden (in German). 10. Auflage, Carl Hanser Verlag 2024. Website: https://esabuch.de
 - [[[starkelorz, Starke+2023a]]] Gernot Starke, Alexander Lorz: Software Architecture Foundation, CPSA Foundation® Exam Preparation. Van Haaren Publishing, 2nd edition, 2023.
 - [[[starkeetalarc42, Starke+2023b]]] Gernot Starke, Michael Simons, Stefan Zörner, Ralf D. Müller, and Hendrik Lösch: arc42-by-Example - Software Architecture Documentation in Practice. Leanpub, 3rd edition 2023. https://leanpub.com/arc42byexample