diff --git a/mariadb/hooks/sql_database-relation-joined b/mariadb/hooks/sql_database-relation-joined
new file mode 100755
index 0000000..c9d906a
--- /dev/null
+++ b/mariadb/hooks/sql_database-relation-joined
@@ -0,0 +1,15 @@
+#!/bin/bash
+
+## When writing relation script, remember:
+##  - they should be idempotents
+##  - they can be launched while the dockers is already up
+##  - they are launched from the host
+##  - the target of the link is launched first, and get a chance to ``relation-set``
+##  - both side of the scripts get to use ``relation-get``.
+
+relation-set type mysql || {
+    err "Could not set relation ${WHITE}type${NORMAL} to 'mysql'."
+    exit 1
+}
+
+. hooks/mysql_database-relation-joined
\ No newline at end of file
diff --git a/mariadb/metadata.yml b/mariadb/metadata.yml
index 676e493..4a8d9b4 100644
--- a/mariadb/metadata.yml
+++ b/mariadb/metadata.yml
@@ -2,6 +2,7 @@ name: MariaDB
 maintainer: "Valentin Lab <valentin.lab@kalysto.org>"
 provides:
   mysql-database:
+  sql-database:
 data-resources:
   - /var/lib/mysql
   - /var/backups/mysql
diff --git a/nextcloud/hooks/mysql_database-relation-joined b/nextcloud/hooks/mysql_database-relation-joined
deleted file mode 100755
index 792d8f4..0000000
--- a/nextcloud/hooks/mysql_database-relation-joined
+++ /dev/null
@@ -1,51 +0,0 @@
-#!/bin/bash
-
-. lib/common
-
-set -e
-
-PASSWORD="$(relation-get password)"
-USER="$(relation-get user)"
-DBNAME="$(relation-get dbname)"
-
-
-## This check adds purely arbitrary limits to what could be a password
-## if we need to open that more, just consider the next script where we'll
-## need to write in a PHP structure, or in YAML structure.
-
-## Note that here, "[]" chars are not accepted just because it doesn't seem evident
-## to test for those in bash.
-if ! [[ "$PASSWORD" =~ ^[a-zA-Z0-9~\`\&+=@\#^\*/\\_%\$:\;\!?.,\<\>{}()\"\'|-]*$ ]]; then
-     err "Invalid password chosen for mysql database."
-     exit 1
-fi
-
-## if config is not existent
-if [ -e "$CONFIGFILE" ] && grep "^  'dbuser' => '" "$CONFIGFILE" >/dev/null; then
-
-    ## 'occ' can't be used as it will try to connect to mysql before running and
-    ## will fail if user/password is not correct
-
-    ## We need to get through bash, and sed interpretation, then PHP single quoted strings.
-    quoted_user="${USER//\\/\\\\\\\\\\}"
-    quoted_user="${quoted_user//\'/\\\\\'}"
-    quoted_password="${PASSWORD//\\/\\\\\\\\\\}"
-    quoted_password="${quoted_password//\'/\\\\\'}"
-    sed -ri "s/^(  'dbuser' => ')(.*)(',)$/\1${quoted_user}\3/g;\
-             s/^(  'dbpassword' => ')(.*)(',)$/\1${quoted_password}\3/g;" "$CONFIGFILE"
-else
-
-    ## These variable are not used by current docker image after first install
-
-    config-add "\
-services:
-  $MASTER_BASE_SERVICE_NAME:
-    environment:
-      MYSQL_HOST: $MASTER_TARGET_SERVICE_NAME
-      MYSQL_DATABASE: $DBNAME
-      MYSQL_PASSWORD: $PASSWORD
-      MYSQL_USER: $USER
-"
-fi
-
-info "Configured $SERVICE_NAME code for $TARGET_SERVICE_NAME access."
diff --git a/nextcloud/hooks/mysql_database-relation-joined b/nextcloud/hooks/mysql_database-relation-joined
new file mode 120000
index 0000000..c54b577
--- /dev/null
+++ b/nextcloud/hooks/mysql_database-relation-joined
@@ -0,0 +1 @@
+postgres_database-relation-joined
\ No newline at end of file
diff --git a/nextcloud/hooks/postgres_database-relation-joined b/nextcloud/hooks/postgres_database-relation-joined
index ff60bb5..d75bda6 100755
--- a/nextcloud/hooks/postgres_database-relation-joined
+++ b/nextcloud/hooks/postgres_database-relation-joined
@@ -1,51 +1,11 @@
 #!/bin/bash
 
-. lib/common
+type="${0##*/}"
+type="${type%_database-relation-joined}"
 
-set -e
+set-relation type "$type" || {
+    err "Could not set relation ${WHITE}type${NORMAL} to '$type'."
+    exit 1
+}
 
-PASSWORD="$(relation-get password)"
-USER="$(relation-get user)"
-DBNAME="$(relation-get dbname)"
-
-
-## This check adds purely arbitrary limits to what could be a password
-## if we need to open that more, just consider the next script where we'll
-## need to write in a PHP structure, or in YAML structure.
-
-## Note that here, "[]" chars are not accepted just because it doesn't seem evident
-## to test for those in bash.
-if ! [[ "$PASSWORD" =~ ^[a-zA-Z0-9~\`\&+=@\#^\*/\\_%\$:\;\!?.,\<\>{}()\"\'|-]*$ ]]; then
-     err "Invalid password chosen for postgres database."
-     exit 1
-fi
-
-## if config is not existent
-if [ -e "$CONFIGFILE" ] && grep "^  'dbuser' => '" "$CONFIGFILE" >/dev/null; then
-
-    ## 'occ' can't be used as it will try to connect to postgres before running and
-    ## will fail if user/password is not correct
-
-    ## We need to get through bash, and sed interpretation, then PHP single quoted strings.
-    quoted_user="${USER//\\/\\\\\\\\\\}"
-    quoted_user="${quoted_user//\'/\\\\\'}"
-    quoted_password="${PASSWORD//\\/\\\\\\\\\\}"
-    quoted_password="${quoted_password//\'/\\\\\'}"
-    sed -ri "s/^(  'dbuser' => ')(.*)(',)$/\1${quoted_user}\3/g;\
-             s/^(  'dbpassword' => ')(.*)(',)$/\1${quoted_password}\3/g;" "$CONFIGFILE"
-else
-
-    ## These variable are not used by current docker image after first install
-
-    config-add "\
-services:
-  $MASTER_BASE_SERVICE_NAME:
-    environment:
-      POSTGRES_HOST: $MASTER_TARGET_SERVICE_NAME
-      POSTGRES_DB: $DBNAME
-      POSTGRES_PASSWORD: $PASSWORD
-      POSTGRES_USER: $USER
-"
-fi
-
-info "Configured $SERVICE_NAME code for $TARGET_SERVICE_NAME access."
+. ./hooks/sql_database-relation-joined
diff --git a/nextcloud/hooks/sql_database-relation-joined b/nextcloud/hooks/sql_database-relation-joined
new file mode 100755
index 0000000..7ae6ea7
--- /dev/null
+++ b/nextcloud/hooks/sql_database-relation-joined
@@ -0,0 +1,60 @@
+#!/bin/bash
+
+. lib/common
+
+set -e
+TYPE="$(relation-get type)" || {
+    err "No ${WHITE}type${NORMAL} set in relation."
+    exit 1
+}
+PASSWORD="$(relation-get password)"
+USER="$(relation-get user)"
+DBNAME="$(relation-get dbname)"
+
+
+## This check adds purely arbitrary limits to what could be a password
+## if we need to open that more, just consider the next script where we'll
+## need to write in a PHP structure, or in YAML structure.
+
+## Note that here, "[]" chars are not accepted just because it doesn't seem evident
+## to test for those in bash.
+if ! [[ "$PASSWORD" =~ ^[a-zA-Z0-9~\`\&+=@\#^\*/\\_%\$:\;\!?.,\<\>{}()\"\'|-]*$ ]]; then
+     err "Invalid password chosen for $type database."
+     exit 1
+fi
+
+## if config is not existent
+if [ -e "$CONFIGFILE" ] && grep "^  'dbuser' => '" "$CONFIGFILE" >/dev/null; then
+
+    ## 'occ' can't be used as it will try to connect to db before running and
+    ## will fail if user/password is not correct
+
+    ## We need to get through bash, and sed interpretation, then PHP single quoted strings.
+    quoted_user="${USER//\\/\\\\\\\\\\}"
+    quoted_user="${quoted_user//\'/\\\\\'}"
+    quoted_password="${PASSWORD//\\/\\\\\\\\\\}"
+    quoted_password="${quoted_password//\'/\\\\\'}"
+    sed -ri "s/^(  'dbuser' => ')(.*)(',)$/\1${quoted_user}\3/g;\
+             s/^(  'dbpassword' => ')(.*)(',)$/\1${quoted_password}\3/g;" "$CONFIGFILE"
+else
+
+    ## These variable are not used by current docker image after first install
+
+    if [ "$TYPE" == "mysql" ]; then
+        database_env_label="DATABASE"
+    else
+        database_env_label="DB"
+    fi
+
+    config-add "\
+services:
+  $MASTER_BASE_SERVICE_NAME:
+    environment:
+      ${TYPE^^}_HOST: $MASTER_TARGET_SERVICE_NAME
+      ${TYPE^^}_${database_env_label}: $DBNAME
+      ${TYPE^^}_PASSWORD: $PASSWORD
+      ${TYPE^^}_USER: $USER
+"
+fi
+
+info "Configured $SERVICE_NAME code for $TARGET_SERVICE_NAME access."
diff --git a/nextcloud/metadata.yml b/nextcloud/metadata.yml
index 196eb08..215cddf 100644
--- a/nextcloud/metadata.yml
+++ b/nextcloud/metadata.yml
@@ -7,20 +7,13 @@ config-resources:
 provides:
   nextcloud-app:
 uses:
-  postgres-database:
+  sql-database:
     #constraint: required | recommended | optional
     #auto: pair | summon | none ## default: pair
     constraint: required
     auto: summon
     solves:
       database: "main storage"
-  mysql-database:
-    #constraint: required | recommended | optional
-    #auto: pair | summon | none ## default: pair
-    constraint: optional
-    auto: pair
-    solves:
-      database: "main storage"
   web-proxy:
     #constraint: required | recommended | optional
     #auto: pair | summon | none ## default: pair
diff --git a/postgres/hooks/sql_database-relation-joined b/postgres/hooks/sql_database-relation-joined
new file mode 100755
index 0000000..75fac30
--- /dev/null
+++ b/postgres/hooks/sql_database-relation-joined
@@ -0,0 +1,16 @@
+#!/bin/bash
+
+## When writing relation script, remember:
+##  - they should be idempotents
+##  - they can be launched while the dockers is already up
+##  - they are launched from the host
+##  - the target of the link is launched first, and get a chance to ``relation-set``
+##  - both side of the scripts get to use ``relation-get``.
+
+relation-set type postgres || {
+    err "Could not set relation ${WHITE}type${NORMAL} to 'postgres'."
+    exit 1
+}
+
+. hooks/postgres_database-relation-joined
+
diff --git a/postgres/metadata.yml b/postgres/metadata.yml
index 4191144..bda14c6 100644
--- a/postgres/metadata.yml
+++ b/postgres/metadata.yml
@@ -4,6 +4,7 @@ data-resources:
   - /var/lib/postgresql/data
 provides:
   postgres-database:
+  sql-database:
 
 uses:
   schedule-command: