diff --git a/.gitmodules b/.gitmodules
index d81948d..61ac8c6 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -1,3 +1,6 @@
 [submodule ".md-ddl"]
 	path = .md-ddl
 	url = https://github.com/Semprini/md-ddl
+[submodule "semprini-data-domain"]
+	path = .semprini-data-domain
+	url = https://git.semprini.me/paul/semprini-data-domain.git
diff --git a/.semprini-data-domain b/.semprini-data-domain
new file mode 160000
index 0000000..2f417e6
--- /dev/null
+++ b/.semprini-data-domain
@@ -0,0 +1 @@
+Subproject commit 2f417e6d1d03613f04e1146d26b4d834ec39eb10