diff --git a/schema/000_immutable.sql b/schema/000_immutable.sql
new file mode 100644
index 0000000..7238e8f
--- /dev/null
+++ b/schema/000_immutable.sql
@@ -0,0 +1,43 @@
+create function mark_columns_immutable(schema text, table_ text, columns text[])
+  returns void
+  language plpgsql
+  as $$
+declare
+  col text;
+  qualified_name text := concat(schema, '.', table_);
+  do_table_immutable_columns text := concat('do_', table_, '_immutable_columns');
+  trigger_table_immutable_columns text := concat('trigger_', table_, '_immutable_columns');
+  create_do_table_immutable_columns text;
+  create_trigger_table_immutable_columns text;
+begin
+  create_do_table_immutable_columns := concat( create_do_table_immutable_columns
+                                             , 'create function ', schema, '.', do_table_immutable_columns, E'() returns trigger language plpgsql as \$\$\n'
+                                             , E'begin\n'
+                                             , '  if OLD.', columns[1], ' <> NEW.', columns[1], E' then\n'
+                                             , E'    raise exception \'', qualified_name, '.', columns[1], E' is immutable\' using errcode = \'restrict_violation\';\n'
+                                             );
+  foreach col in array columns[2:] loop
+    create_do_table_immutable_columns := concat( create_do_table_immutable_columns
+                                               , E'  elsif OLD.', col, ' <> NEW.', col, E' then\n'
+                                               , E'    raise exception \'', qualified_name, '.', col, E' is immutable\' using errcode = \'restrict_violation\';\n'
+                                               );
+  end loop;
+
+  create_do_table_immutable_columns := concat( create_do_table_immutable_columns
+                                             , E'  end if;\n'
+                                             , E'\n'
+                                             , E'  return NEW;\n'
+                                             , E'end;\n'
+                                             , E'\$\$;\n'
+                                             );
+
+  create_trigger_table_immutable_columns := concat( create_trigger_table_immutable_columns
+                                                  , 'create trigger ', trigger_table_immutable_columns, E'\n'
+                                                  , 'before update on ', qualified_name, E'\n'
+                                                  , 'for each row execute function ', do_table_immutable_columns, '();'
+                                                  );
+
+  execute create_do_table_immutable_columns;
+  execute create_trigger_table_immutable_columns;
+end;
+$$;
diff --git a/schema/020_thread.sql b/schema/020_thread.sql
deleted file mode 100644
index 49f0a94..0000000
--- a/schema/020_thread.sql
+++ /dev/null
@@ -1,11 +0,0 @@
-create type public.thread_kind as enum
-  ( 'post'
-  , 'short'
-  , 'message'
-  );
-
-create table public.thread
-  ( id     int                not null primary key generated always as identity
-  , uid    uuid               not null default gen_random_uuid()
-  , kind   public.thread_kind not null
-  );
diff --git a/schema/020_user.sql b/schema/020_user.sql
index fd1b8df..1fe71fa 100644
--- a/schema/020_user.sql
+++ b/schema/020_user.sql
@@ -16,3 +16,10 @@ select setup_audit_and_soft_delete( 'public'
                                          , row('email', 'public.email')
                                          ] :: audited_column[]
                                   );
+
+select mark_columns_immutable( 'public'
+                             , 'usr'
+                             , array[ 'id'
+                                    , 'uid'
+                                    ]
+                             );
diff --git a/schema/021_thread.sql b/schema/021_thread.sql
new file mode 100644
index 0000000..26788c2
--- /dev/null
+++ b/schema/021_thread.sql
@@ -0,0 +1,70 @@
+create type public.thread_kind as enum
+  ( 'feed'
+  , 'message_feed'
+  , 'message'
+  , 'post_feed'
+  , 'post'
+  , 'comment'
+  , 'symbolic'
+  );
+
+create table public.thread
+  ( id        int                not null primary key generated always as identity
+  , uid       uuid               not null default gen_random_uuid()
+  , deleted   boolean            not null default false
+  , kind      public.thread_kind not null
+  );
+
+select setup_audit_and_soft_delete('public', 'thread', array[] :: audited_column[]);
+select mark_columns_immutable('public', 'thread', array['id', 'uid', 'kind']);
+
+create table public.thread_feed
+  ( id        int     not null primary key generated always as identity
+  , uid       uuid    not null default gen_random_uuid()
+  , deleted   boolean not null default false
+  , thread    int     not null references public.thread(id)
+  -- , community int     not null references public.community(id)
+  );
+
+select setup_audit_and_soft_delete('public', 'thread_feed', array[] :: audited_column[]);
+select mark_columns_immutable('public', 'thread_feed', array['id', 'uid', 'thread', 'community']);
+
+create type public.thread_attachment_kind as enum 
+  ( 'vote'
+  , 'emoji'
+  );
+
+create type public.thread_attachment_vote_direction as enum 
+  ( 'up'
+  , 'down'
+  );
+
+create table public.thread_attachment
+  ( id     int                           not null primary key generated always as identity
+  , uid    uuid                          not null default gen_random_uuid()
+  , thread int                           not null references public.thread(id)
+  , kind   public.thread_attachment_kind not null
+  );
+
+select setup_audit_and_soft_delete('public', 'thread_attachment', array[] :: audited_column[]);
+select mark_columns_immutable('public', 'thread_attachment', array['id', 'uid', 'thread', 'kind']);
+
+create table public.thread_attachment_emoji
+  ( id                int  not null primary key generated always as identity
+  , uid               uuid not null default gen_random_uuid()
+  , thread_attachment int  not null references public.thread_attachment(id)
+  , emoji             text not null
+  );
+
+select setup_audit_and_soft_delete('public', 'thread_attachment_emoji', array[] :: audited_column[]);
+select mark_columns_immutable('public', 'thread_attachment_emoji', array['id', 'uid', 'thread_attachment', 'emoji']);
+
+create table public.thread_attachment_vote
+  ( id                int                                     not null primary key generated always as identity
+  , uid               uuid                                    not null default gen_random_uuid()
+  , thread_attachment int                                     not null references public.thread_attachment(id)
+  , direction         public.thread_attachment_vote_direction not null
+  );
+
+select setup_audit_and_soft_delete('public', 'thread_attachment_vote', array[] :: audited_column[]);
+select mark_columns_immutable('public', 'thread_attachment_vote', array['id', 'uid', 'thread_attachment', 'direction']);