diff --git a/api/__init__.py b/api/__init__.py
index 47b16ae..a10ca2b 100644
--- a/api/__init__.py
+++ b/api/__init__.py
@@ -22,6 +22,8 @@ from .database import read, try_read, read_all, write
 
 from .batch_exe import execute_batch_commands, execute_batch_command
 
+from .extension_data import get_all_extension_data_keys, get_all_extension_data, get_extension_data, set_extension_data
+
 from .s0_base import JUNCTION, RESERVOIR, TANK, PIPE, PUMP, VALVE, PATTERN, CURVE
 from .s0_base import is_node, is_junction, is_reservoir, is_tank
 from .s0_base import is_link, is_pipe, is_pump, is_valve
diff --git a/api/batch_exe.py b/api/batch_exe.py
index 7f28c4e..4b82497 100644
--- a/api/batch_exe.py
+++ b/api/batch_exe.py
@@ -1,6 +1,7 @@
 from typing import Any
 from .sections import *
 from .database import API_ADD, API_UPDATE, API_DELETE, ChangeSet, write, read, read_all, get_current_operation
+from .extension_data import set_extension_data
 from .s1_title import set_title
 from .s2_junctions import set_junction, add_junction, delete_junction
 from .s3_reservoirs import set_reservoir, add_reservoir, delete_reservoir
@@ -112,6 +113,8 @@ def _execute_add_command(name: str, cs: ChangeSet) -> ChangeSet:
 def _execute_update_command(name: str, cs: ChangeSet) -> ChangeSet:
     type = cs.operations[0]['type']
 
+    if type == 'extension_data':
+        return set_extension_data(name, cs)
     if type == s1_title:
         return set_title(name, cs)
     if type == s2_junction:
diff --git a/api/extension_data.py b/api/extension_data.py
new file mode 100644
index 0000000..cfce4ea
--- /dev/null
+++ b/api/extension_data.py
@@ -0,0 +1,62 @@
+from .database import *
+
+
+def get_all_extension_data_keys(name: str) -> list[str]:
+    result: list[str] = []
+    for row in read_all(name, 'select key from extension_data'):
+        result.append(row['key'])
+    return result
+
+
+def get_all_extension_data(name: str) -> dict[str, Any]:
+    result: dict[str, Any] = {}
+    for row in read_all(name, 'select key, value from extension_data'):
+        result[row['key']] = row['value']
+    return result
+
+
+def get_extension_data(name: str, key: str) -> str | None:
+    if key == None or key == '':
+        return None
+    row = try_read(name, f"select value from extension_data where key = '{key}'")
+    if row == None:
+        return None
+    return row['value']
+
+
+def _set_extension_data(name: str, cs: ChangeSet) -> DbChangeSet:
+    op = cs.operations[0]
+    key, new_val = op['key'], op['value']
+
+    f_new_val = f"'{new_val}'" if new_val != None else 'null'
+
+    old_val = get_extension_data(name, key)
+    f_old_val = f"'{old_val}'" if old_val != None else 'null'
+
+    redo_sql = f"delete from extension_data where key = '{key}';"
+    if new_val != None:
+        redo_sql += f"insert into extension_data (key, value) values ('{key}', {f_new_val});"
+
+    undo_sql = f"delete from extension_data where key = '{key}';"
+    if old_val != None:
+        undo_sql += f"insert into extension_data (key, value) values ('{key}', {f_old_val});"
+
+    redo_cs = g_update_prefix | { 'type': 'extension_data', 'key': key, 'value': new_val }
+    undo_cs = g_update_prefix | { 'type': 'extension_data', 'key': key, 'value': old_val }
+
+    return DbChangeSet(redo_sql, undo_sql, [redo_cs], [undo_cs])
+
+
+def set_extension_data(name: str, cs: ChangeSet) -> ChangeSet:
+    if len(cs.operations) != 1:
+        return ChangeSet()
+
+    op = cs.operations[0]
+    if 'key' not in op or 'value' not in op:
+        return ChangeSet()
+
+    key = op['key']
+    if key == None or key == '':
+        return ChangeSet()
+
+    return execute_command(name, _set_extension_data(name, cs))
diff --git a/create_template.py b/create_template.py
index c0260c2..80f2126 100644
--- a/create_template.py
+++ b/create_template.py
@@ -34,11 +34,13 @@ sql_create = [
     "script/sql/create/30.scada_device_data.sql",
     "script/sql/create/31.scada_element.sql",
     "script/sql/create/32.region.sql",
+    "script/sql/create/extension_data.sql",
     "script/sql/create/operation.sql"
 ]
 
 sql_drop = [
     "script/sql/drop/operation.sql",
+    "script/sql/create/extension_data.sql",
     "script/sql/drop/32.region.sql",
     "script/sql/drop/31.scada_element.sql",
     "script/sql/drop/30.scada_device_data.sql",
diff --git a/script/sql/create/extension_data.sql b/script/sql/create/extension_data.sql
new file mode 100644
index 0000000..491cbaf
--- /dev/null
+++ b/script/sql/create/extension_data.sql
@@ -0,0 +1,5 @@
+create table extension_data
+(
+  key   text primary key
+, value text not null
+);
diff --git a/script/sql/drop/extension_data.sql b/script/sql/drop/extension_data.sql
new file mode 100644
index 0000000..ba82d5f
--- /dev/null
+++ b/script/sql/drop/extension_data.sql
@@ -0,0 +1 @@
+drop table if exists extension_data;
diff --git a/test_tjnetwork.py b/test_tjnetwork.py
index bdbf5b4..7a239f9 100644
--- a/test_tjnetwork.py
+++ b/test_tjnetwork.py
@@ -203,6 +203,81 @@ class TestApi:
         self.leave(p)
 
 
+    # extension_data
+
+
+    def test_extension_data(self):
+        p = 'test_extension_data'
+        self.enter(p)
+
+        assert get_all_extension_data_keys(p) == []
+        assert get_all_extension_data(p) == {}
+        assert get_extension_data(p, '') == None
+
+        set_extension_data(p, ChangeSet({'key': 'key', 'value': None}))
+        assert get_extension_data(p, 'key') == None
+
+        set_extension_data(p, ChangeSet({'key': 'key', 'value': ''}))
+        assert get_extension_data(p, 'key') == ''
+
+        set_extension_data(p, ChangeSet({'key': 'key', 'value': 'value'}))
+        assert get_extension_data(p, 'key') == 'value'
+
+        set_extension_data(p, ChangeSet({'key': 'key', 'value': 'val'}))
+        assert get_extension_data(p, 'key') == 'val'
+
+        set_extension_data(p, ChangeSet({'key': 'key1', 'value': 'val1'}))
+        assert get_extension_data(p, 'key1') == 'val1'
+
+        assert get_all_extension_data_keys(p) == ['key', 'key1']
+        assert get_all_extension_data(p) == {'key': 'val', 'key1': 'val1'}
+
+        self.leave(p)
+
+
+    def test_extension_data_op(self):
+        p = 'test_extension_data_op'
+        self.enter(p)
+
+        cs = set_extension_data(p, ChangeSet({'key': 'key', 'value': ''})).operations[0]
+        assert cs['operation'] == API_UPDATE
+        assert cs['type'] == 'extension_data'
+        assert cs['key'] == 'key'
+        assert cs['value'] == ''
+
+        cs = execute_undo(p).operations[0]
+        assert cs['operation'] == API_UPDATE
+        assert cs['type'] == 'extension_data'
+        assert cs['key'] == 'key'
+        assert cs['value'] == None
+
+        cs = execute_redo(p).operations[0]
+        assert cs['operation'] == API_UPDATE
+        assert cs['type'] == 'extension_data'
+        assert cs['key'] == 'key'
+        assert cs['value'] == ''
+
+        cs = set_extension_data(p, ChangeSet({'key': 'key', 'value': 'value'})).operations[0]
+        assert cs['operation'] == API_UPDATE
+        assert cs['type'] == 'extension_data'
+        assert cs['key'] == 'key'
+        assert cs['value'] == 'value'
+
+        cs = execute_undo(p).operations[0]
+        assert cs['operation'] == API_UPDATE
+        assert cs['type'] == 'extension_data'
+        assert cs['key'] == 'key'
+        assert cs['value'] == ''
+
+        cs = execute_redo(p).operations[0]
+        assert cs['operation'] == API_UPDATE
+        assert cs['type'] == 'extension_data'
+        assert cs['key'] == 'key'
+        assert cs['value'] == 'value'
+
+        self.leave(p)
+
+
     # complex test
 
 
diff --git a/tjnetwork.py b/tjnetwork.py
index 2bdff0f..5181f72 100644
--- a/tjnetwork.py
+++ b/tjnetwork.py
@@ -321,6 +321,23 @@ def write(name: str, sql: str):
     return api.write(name, sql)
 
 
+############################################################
+# extension_data
+############################################################
+
+def get_all_extension_data_keys(name: str) -> list[str]:
+    return api.get_all_extension_data_keys(name)
+
+def get_all_extension_data(name: str) -> dict[str, Any]:
+    return api.get_all_extension_data(name)
+
+def get_extension_data(name: str, key: str) -> str | None:
+    return api.get_extension_data(name, key)
+
+def set_extension_data(name: str, cs: ChangeSet) -> ChangeSet:
+    return api.set_extension_data(name, cs)
+
+
 ############################################################
 # type
 ############################################################