diff --git a/api/__init__.py b/api/__init__.py
index 4cd493b..1d41200 100644
--- a/api/__init__.py
+++ b/api/__init__.py
@@ -5,10 +5,8 @@ from .project import copy_project
 from .change_set import ChangeSet
 
 from .operation import get_current_operation
-from .operation import execute_undo as undo
-from .operation import execute_redo as redo
-from .operation import have_snapshot, take_snapshot, pick_snapshot
-from .operation import have_transaction, start_transaction, commit_transaction, abort_transaction
+from .operation import execute_undo, execute_redo
+from .operation import have_snapshot, take_snapshot, pick_snapshot, sync_with_server
 
 from .s0_base import JUNCTION, RESERVOIR, TANK, PIPE, PUMP, VALVE
 from .s0_base import is_node, is_junction, is_reservoir, is_tank
@@ -20,9 +18,7 @@ from .s0_base import get_node_links
 
 from .s1_title import set_title, get_title
 
-from .s2_junctions import add_junction, delete_junction
-from .s2_junctions import set_junction_elevation, set_junction_demand, set_junction_pattern, set_junction_coord
-from .s2_junctions import get_junction_property_names, get_junction_properties
+from .s2_junctions import get_junction_schema, add_junction, delete_junction, get_junction, set_junction
 
 from .s3_reservoirs import add_reservoir, delete_reservoir
 from .s3_reservoirs import set_reservoir_head, set_reservoir_pattern, set_reservoir_coord
diff --git a/api/operation.py b/api/operation.py
index ef7e081..c746383 100644
--- a/api/operation.py
+++ b/api/operation.py
@@ -1,111 +1,130 @@
 from psycopg.rows import dict_row, Row
 from .connection import g_conn_dict as conn
+from .utility import *
+from .change_set import *
 
-def _get_current_transaction(name: str) -> Row | None:
-    with conn[name].cursor(row_factory=dict_row) as cur:
-        cur.execute(f"select * from transaction_operation")
-        return cur.fetchone()
 
-def _get_current_transaction_id(name: str) -> int:
-    row = _get_current_transaction(name)
-    return int(row['id'])
+API_ADD = 'add'
+API_DELETE = 'delete'
+API_UPDATE = 'update'
 
-def _remove_transaction(name: str) -> None:
-    with conn[name].cursor() as cur:
-        cur.execute(f"delete from transaction_operation")
 
 def _remove_operation(name: str, id: int) -> None:
-    with conn[name].cursor(row_factory=dict_row) as cur:
-        # can not be >= to cascade delete since there is a tree !
-        cur.execute(f"delete from transaction_operation where id = {id}") # this should not happen
-        cur.execute(f"delete from snapshot_operation where id = {id}") # this may happen
-        cur.execute(f"delete from operation where id = {id}")
+    row = read(name, f'select * from operation where parent = {id}')
+    if row != None:
+        raise Exception('Disallow to remove parent operation !')
+
+    sql += f'delete from snapshot_operation where id = {id};'
+    sql += f'delete from operation where id = {id}'
+    write(name, sql)
+
 
 def _get_parents(name: str, id: int) -> list[int]:
     ids = [id]
-    with conn[name].cursor(row_factory=dict_row) as cur:
-        while ids[-1] != 0:
-            cur.execute(f"select parent from operation where id = {ids[-1]}")
-            ids.append(int(cur.fetchone()['parent']))
+    while ids[-1] != 0:
+        row = read(name, f'select parent from operation where id = {ids[-1]}')
+        ids.append(int(row['parent']))
     return ids
 
+
 def get_current_operation(name: str) -> int:
-    with conn[name].cursor(row_factory=dict_row) as cur:
-        cur.execute(f"select id from current_operation")
-        return int(cur.fetchone()['id'])
+    row = read(name, f'select id from current_operation')
+    return int(row['id'])
+
 
 def _update_current_operation(name: str, old_id: int, id: int) -> None:
-    with conn[name].cursor() as cur:
-        cur.execute(f"update current_operation set id = {id} where id = {old_id}")
+    return write(name, f'update current_operation set id = {id} where id = {old_id}')
 
-def _add_redo_undo(name: str, redo: str, undo: str) -> int:
-    with conn[name].cursor(row_factory=dict_row) as cur:
-        parent = get_current_operation(name)
-        cur.execute(f"insert into operation (id, redo, undo, parent) values (default, '{redo}', '{undo}', {parent})")
-        cur.execute("select max(id) from operation")
-        return int(cur.fetchone()['max'])
 
-# execute curr undo
-def _query_undo(name: str, id: str) -> dict[str, str]:
-    with conn[name].cursor(row_factory=dict_row) as cur:
-        cur.execute(f"select undo, parent from operation where id = {id}")
-        return cur.fetchone()
+def _add_redo_undo(name: str, redo: str, undo: str, api_id: str, api_op: str, api_object_type: str, api_object_id: str, api_object_properties: list[str]) -> int:
+    parent = get_current_operation(name)
+    ps = []
+    for p in api_object_properties:
+        ps.append(f'"{p}"')
+    if len(ps) > 0:
+        ps = ','.join(ps)
+        ps = '{' + ps + '}'
+        sql = f"insert into operation (id, redo, undo, parent, api_id, api_op, api_object_type, api_object_id, api_object_properties) values (default, '{redo}', '{undo}', {parent}, '{api_id}', '{api_op}', '{api_object_type}', '{api_object_id}', '{ps}')"
+    else:
+        sql = f"insert into operation (id, redo, undo, parent, api_id, api_op, api_object_type, api_object_id) values (default, '{redo}', '{undo}', {parent}, '{api_id}', '{api_op}', '{api_object_type}', '{api_object_id}')"
+    write(name, sql)
+
+    return int(read(name, 'select max(id) from operation')['max'])
+
+
+def _query_operation(name: str, id: str) -> dict[str, str]:
+    return read(name, f'select * from operation where id = {id}')
+
 
-# execute next redo
 def _query_redo_child(name: str, id: str) -> str:
-    with conn[name].cursor(row_factory=dict_row) as cur:
-        cur.execute(f"select redo_child from operation where id = {id}")
-        return cur.fetchone()['redo_child']
+    row = read(name, f'select redo_child from operation where id = {id}')
+    return row['redo_child']
 
-def _query_redo(name: str, id: str) -> dict[str, str]:
-    with conn[name].cursor(row_factory=dict_row) as cur:
-        cur.execute(f"select redo from operation where id = {id}")
-        return cur.fetchone()['redo']
 
 def _set_redo_child(name: str, id: int, child: int | str) -> None:
-    with conn[name].cursor() as cur:
-        cur.execute(f"update operation set redo_child = {child} where id = {id}")
+    return write(name, f'update operation set redo_child = {child} where id = {id}')
 
-def _execute(name: str, sql: str) -> None:
-    with conn[name].cursor() as cur:
-        sql = sql.replace("\"", "\'")
-        cur.execute(sql)
 
-def add_operation(name: str, redo: str, undo: str) -> None:
-    curr = _add_redo_undo(name, redo, undo)
+def add_operation(name: str, redo: str, undo: str, api_id: str, api_op: str, api_object_type: str, api_object_id: str, api_object_properties: list[str] = []) -> None:
+    curr = _add_redo_undo(name, redo, undo, api_id, api_op, api_object_type, api_object_id, api_object_properties)
     old = get_current_operation(name)
     _update_current_operation(name, old, curr)
 
-def execute_undo(name: str, discard: bool = False) -> None:
+
+def _reverser_op(op: str) -> str:
+    if op == API_ADD:
+        return API_DELETE
+    elif op == API_DELETE:
+        return API_ADD
+    else:
+        return op
+
+
+def _get_change_set(row: dict[str, str], undo: bool) -> ChangeSet:
+    op = row['api_op']
+    if undo:
+        op = _reverser_op(op)
+
+    type = row['api_object_type']
+    id = row['api_object_id']
+
+    change = ChangeSet()
+
+    if op == API_ADD:
+        change.add(type, id)
+    elif op == API_DELETE:
+        change.delete(type, id)
+    elif op == API_UPDATE:
+        ps = row['api_object_properties'].removeprefix('{').removesuffix('}').split(',')
+        change.update(type, id, ps)
+
+    return change
+
+
+def execute_undo(name: str, discard: bool) -> ChangeSet:
     curr = get_current_operation(name)
 
-    # transaction control
-    if have_transaction(name):
-        tran = _get_current_transaction(name)
-        if tran != None and int(tran['id']) >= 0:
-            if bool(tran['strict']): # strict mode disallow undo
-                print("Do not allow to undo in strict transaction mode!")
-                return
-            elif int(tran['id']) >= curr: # normal mode disallow undo start point, and there is foreign key constraint
-                print("Do not allow to undo transaction start point!")
-                return
-
-    row = _query_undo(name, curr)
+    row = _query_operation(name, curr)
     undo = row['undo']
     if undo == '':
         print("nothing to undo!")
         return
 
-    parent = int(row['parent'])
-    _set_redo_child(name, parent, 'NULL' if discard else curr)
+    change = _get_change_set(row, True)
 
-    _execute(name, undo)
+    parent = int(row['parent'])
+    _set_redo_child(name, parent, 'null' if discard else curr)
+
+    write(name, undo)
     _update_current_operation(name, curr, parent)
 
     if discard:
         _remove_operation(name, curr)
 
-def execute_redo(name: str) -> None:
+    return change
+
+
+def execute_redo(name: str) -> ChangeSet:
     curr = get_current_operation(name)
     redoChild = _query_redo_child(name, curr)
     if redoChild == None:
@@ -113,108 +132,127 @@ def execute_redo(name: str) -> None:
         return
     
     child = int(redoChild)
-    redo = _query_redo(name, child)
+    row = _query_operation(name, child)
+    redo = row['redo']
 
-    _execute(name, redo)
+    change = _get_change_set(row, False)
+
+    write(name, redo)
     _update_current_operation(name, curr, child)
 
-# snapshot support to checkout between different version of database
-# snapshot is persistent
-# since redo always remember the recently undo path
+    return change
+
+
+def _get_operation_by_tag(name: str, tag: str) -> int | None:
+    row = read(name, f"select id from snapshot_operation where tag = '{tag}'")
+    return int(row['id']) if row != None else None
+
 
 def have_snapshot(name: str, tag: str) -> bool:
-    with conn[name].cursor(row_factory=dict_row) as cur:
-        cur.execute(f"select id from snapshot_operation where tag = '{tag}'")
-        return cur.rowcount > 0
+    return _get_operation_by_tag(name, tag) != None
 
-def take_snapshot(name: str, tag: str) -> None:
+
+def take_snapshot(name: str, tag: str) -> int | None:
     if tag == None or tag == '':
         print('Non empty tag is expected!')
-        return
+        return None
 
     curr = get_current_operation(name)
+    write(name, f"insert into snapshot_operation (id, tag) values ({curr}, '{tag}')")
+    return curr
 
-    with conn[name].cursor() as cur:
-        cur.execute(f"insert into snapshot_operation (id, tag) values ({curr}, '{tag}')")
 
-def pick_snapshot(name: str, tag: str) -> None:
+def pick_snapshot(name: str, tag: str, discard: bool) -> ChangeSet:
     if tag == None or tag == '':
         print('Non empty tag is expected!')
-        return
+        return ChangeSet()
 
-    if not have_snapshot(name, tag):
+    target = _get_operation_by_tag(name, tag)
+    if target == None:
         print('No such snapshot!')
-        return
+        return ChangeSet()
 
     curr = get_current_operation(name)
+
     curr_parents = _get_parents(name, curr)
+    target_parents = _get_parents(name, target)
 
-    with conn[name].cursor(row_factory=dict_row) as cur:
-        cur.execute(f"select id from snapshot_operation where tag = '{tag}'")
-        target = int(cur.fetchone()['id'])
-        if target in curr_parents: # target -> curr
-            for i in range(curr_parents.index(target)):
-                execute_undo(name)
-        else:
-            target_parents = _get_parents(name, target)
-            if curr in target_parents: # curr -> target
-                for i in range(target_parents.index(curr)):
-                    execute_redo(name)
-            else:
-                ancestor_index = -1
-                while curr_parents[ancestor_index] == target_parents[ancestor_index]:
-                    ancestor_index -= 1
+    change = ChangeSet()
 
-                # ancestor -> curr
-                ancestor = curr_parents[ancestor_index + 1] # ancestor_index + 1 is common parent
-                for i in range(curr_parents.index(ancestor)):
-                    execute_undo(name)
-                # ancestor -> redo, need assign redo_child
-                while target_parents[ancestor_index] != target:
-                    cur.execute(f"update operation set redo_child = '{target_parents[ancestor_index]}' where id = '{target_parents[ancestor_index + 1]}'")
-                    execute_redo(name)
-                    ancestor_index -= 1
-                cur.execute(f"update operation set redo_child = '{target}' where id = '{target_parents[1]}'")
-                execute_redo(name)
+    if target in curr_parents:
+        for _ in range(curr_parents.index(target)):
+            change.append(execute_undo(name, discard))
 
-# transaction is volatile, commit/abort will destroy transaction.
-# can not redo an aborted transaction.
-# but can undo a committed transaction... inconsistent...
-# it may remove snapshot if it is in aborted transaction
+    elif curr in target_parents:
+        target_parents.reverse()
+        curr_index = target_parents.index(curr)
+        for i in range(curr_index, len(target_parents) - 1):
+            write(name, f"update operation set redo_child = '{target_parents[i + 1]}' where id = '{target_parents[i]}'")
+            change.append(execute_redo(name))
 
-def have_transaction(name: str) -> bool:
-    with conn[name].cursor(row_factory=dict_row) as cur:
-        cur.execute(f"select * from transaction_operation")
-        return cur.rowcount > 0
+    else:
+        ancestor_index = -1
+        while curr_parents[ancestor_index] == target_parents[ancestor_index]:
+            ancestor_index -= 1
+        ancestor = curr_parents[ancestor_index + 1]
 
-def start_transaction(name: str, strict: bool = False) -> None:
-    if have_transaction(name):
-        print("Only support single transaction now, please commit/abort current transaction!")
-        return
+        for _ in range(curr_parents.index(ancestor)):
+            change.append(execute_undo(name, discard))
 
-    curr = get_current_operation(name)
+        target_parents.reverse()
+        curr_index = target_parents.index(ancestor)
+        for i in range(curr_index, len(target_parents) - 1):
+            write(name, f"update operation set redo_child = '{target_parents[i + 1]}' where id = '{target_parents[i]}'")
+            change.append(execute_redo(name))
 
-    with conn[name].cursor() as cur:
-        cur.execute(f"insert into transaction_operation (id, strict) values ({curr}, {strict});")
+    return change.compress()
 
-def commit_transaction(name: str) -> None:
-    if not have_transaction(name):
-        print("No active transaction!")
-        return
 
-    _remove_transaction(name)
+def get_change_set(name: str, operation: int, undo: bool) -> ChangeSet:
+    row = read(name, f'select api_id, api_op, api_object_type, api_object_id, api_object_properties from operation where id = {operation}')
+    return _get_change_set(row, undo)
 
-def abort_transaction(name: str) -> None:
-    if not have_transaction(name):
-        print("No active transaction!")
-        return
 
-    tran = _get_current_transaction_id(name)
+def get_current_change_set(name: str) -> ChangeSet:
+    return get_change_set(name, get_current_operation(name), False)
 
-    curr = get_current_operation(name)
-    curr_parents = _get_parents(name, curr)
 
-    for i in range(curr_parents.index(tran)):
-        execute_undo(name, True)
-    
-    _remove_transaction(name)
+def sync_with_server(name: str, operation: int) -> ChangeSet:
+    fr = operation
+    to = get_current_operation(name)
+
+    fr_parents = _get_parents(name, fr)
+    to_parents = _get_parents(name, to)
+
+    change = ChangeSet()
+
+    if fr in to_parents:
+        index = to_parents.index(fr) - 1
+        while index >= 0:
+            change.append(get_change_set(name, to_parents[index], False))
+            index -= 1
+
+    elif to in fr_parents:
+        index = 0
+        while index <= fr_parents.index(to) - 1:
+            change.append(get_change_set(name, fr_parents[index], True))
+            index += 1
+
+    else:
+        ancestor_index = -1
+        while fr_parents[ancestor_index] == to_parents[ancestor_index]:
+            ancestor_index -= 1
+
+        ancestor = fr_parents[ancestor_index + 1]
+
+        index = 0
+        while index <= fr_parents.index(ancestor) - 1:
+            change.append(get_change_set(name, fr_parents[index], True))
+            index += 1
+
+        index = to_parents.index(ancestor) - 1
+        while index >= 0:
+            change.append(get_change_set(name, to_parents[index], False))
+            index -= 1
+
+    return change.compress()
diff --git a/api/s0_base.py b/api/s0_base.py
index c966e66..6a01d9b 100644
--- a/api/s0_base.py
+++ b/api/s0_base.py
@@ -99,15 +99,15 @@ def add_node(name: str, node_type: str, id: str, x: float, y: float, table_sql:
         return ChangeSet()
 
     with conn[name].cursor() as cur:
-        sql = f"insert into _node (id, type) values ('{id}', '{node_type}'); "
+        sql = f"insert into _node (id, type) values ('{id}', '{node_type}');"
         sql += table_sql
-        sql += f" insert into coordinates (node, coord) values ('{id}', '({x}, {y})');"
+        sql += f"insert into coordinates (node, coord) values ('{id}', '({x}, {y})');"
         cur.execute(sql)
 
         redo = sql.replace("'", '"')
-        undo = f'delete from coordinates where node = "{id}"; '
+        undo = f'delete from coordinates where node = "{id}";'
         undo += table_undo_sql
-        undo += f' delete from _node where id = "{id}";'
+        undo += f'delete from _node where id = "{id}";'
         add_operation(name, redo, undo)
 
     change = ChangeSet()
@@ -133,9 +133,9 @@ def delete_node(name: str, node_type: str, id: str, table_sql: str, table_undo_s
         cur.execute(sql)
 
         redo = sql.replace("'", '"')
-        undo = f'insert into _node (id, type) values ("{id}", "{node_type}"); '
+        undo = f'insert into _node (id, type) values ("{id}", "{node_type}");'
         undo += table_undo_sql
-        undo += f' insert into coordinates (node, coord) values ("{id}", "{coord}");'
+        undo += f'insert into coordinates (node, coord) values ("{id}", "{coord}");'
         add_operation(name, redo, undo)
 
     change = ChangeSet()
@@ -148,13 +148,13 @@ def add_link(name: str, link_type: str, id: str, table_sql: str, table_undo_sql:
         return ChangeSet()
 
     with conn[name].cursor() as cur:
-        sql = f"insert into _link (id, type) values ('{id}', '{link_type}'); "
+        sql = f"insert into _link (id, type) values ('{id}', '{link_type}');"
         sql += table_sql
         cur.execute(sql)
 
         redo = sql.replace("'", '"')
         undo = table_undo_sql
-        undo += f' delete from _link where id = "{id}";'
+        undo += f'delete from _link where id = "{id}";'
         add_operation(name, redo, undo)
 
     change = ChangeSet()
diff --git a/api/s24_coordinates.py b/api/s24_coordinates.py
index ddb8df1..0f5ed48 100644
--- a/api/s24_coordinates.py
+++ b/api/s24_coordinates.py
@@ -5,10 +5,8 @@ from .operation import *
 from .change_set import ChangeSet
 
 
-def _to_point(coord: str) -> dict[str, float]:
-    coord = coord.removeprefix('(')
-    coord = coord.removesuffix(')')
-    coord = coord.split(',')
+def _to_client_point(coord: str) -> dict[str, float]:
+    coord = coord.removeprefix('(').removesuffix(')').split(',')
     return { 'x': float(coord[0]), 'y': float(coord[1]) }
 
 
@@ -20,7 +18,7 @@ def get_node_coord(name: str, id: str) -> dict[str, float] | None:
             return None
         
         coord = str(row['coord'])
-        return _to_point(coord)
+        return _to_client_point(coord)
 
 
 def set_node_coord(name: str, node_type: str, id: str, x: float, y: float) -> ChangeSet:
diff --git a/api/s2_junctions.py b/api/s2_junctions.py
index fdfee6d..ac775c3 100644
--- a/api/s2_junctions.py
+++ b/api/s2_junctions.py
@@ -4,82 +4,98 @@ from .s0_base import *
 from .change_set import ChangeSet
 from .s24_coordinates import *
 from .utility import *
+from .schema import *
+
+
+schema: dict[str, dict[str, Any]] = { \
+    'id'        : define_property(str_type, False, True), \
+    'elevation' : define_property(float_type), \
+    'demand'    : define_property(float_type, True), \
+    'pattern'   : define_property(str_type, True), \
+    'coord'     : define_property(client_point_type), \
+    'links'     : define_property(str_list_type, False, True)}
+
+
+def get_junction_schema(name: str) -> dict[str, str]:
+    return schema
+
+
+def _query_junction(name: str, id: str) -> Row | None:
+    return read(name, f"select id, elevation, demand, pattern from junctions where id = '{id}'")
 
 
 def add_junction(name: str, id: str, x: float, y: float, elevation: float) -> ChangeSet:
-    sql = f"insert into junctions (id, elevation) values ('{id}', {elevation});"
-    undo_sql = f'delete from junctions where id = "{id}";'
-    return add_node(name, JUNCTION, id, x, y, sql, undo_sql)
-
-
-def _get_junction(name: str, id: str) -> Row | None:
-    return query(name, f"select elevation, demand, pattern from junctions where id = '{id}'")
-
-
-def delete_junction(name: str, id: str) -> ChangeSet:
-    if not is_junction(name, id):
+    if is_junction(name, id):
         return ChangeSet()
 
-    row = _get_junction(name, id)
-    if row == None:
-        return ChangeSet()
+    sql = f"insert into _node (id, type) values ('{id}', '{JUNCTION}');"
+    sql += f"\ninsert into junctions (id, elevation) values ('{id}', {elevation});"
+    sql += f"\ninsert into coordinates (node, coord) values ('{id}', '({x}, {y})');"
 
-    elevation = row['elevation']
-    demand = decorate(row['demand'], 'float', True)
-    pattern = decorate(row['pattern'], 'str', True)
+    undo = f"delete from coordinates where node = ''{id}'';"
+    undo += f"\ndelete from junctions where id = ''{id}'';"
+    undo += f"\ndelete from _node where id = ''{id}'';"
 
-    sql = f"delete from junctions where id = '{id}';"
-    undo_sql = f'insert into junctions (id, elevation, demand, pattern) values ("{id}", {elevation}, {demand}, {pattern});'
-
-    return delete_node(name, JUNCTION, id, sql, undo_sql)
+    write(name, sql)
+    add_operation(name, sql.replace("'", "''"), undo, 'add_junction', API_ADD, JUNCTION, id)
+    return get_current_change_set(name)
 
 
-def _set_junction(name: str, id: str, key: str, key_type: str, value: str, optional: bool = False) -> ChangeSet:
-    if not is_junction(name, id):
-        return ChangeSet()
-
-    row = _get_junction(name, id)
-    if row == None:
-        return ChangeSet()
-
-    return update(name, JUNCTION, 'junctions', 'id', id, key, key_type, row[key], value, optional)
-
-
-def set_junction_elevation(name: str, id: str, elevation: float) -> ChangeSet:
-    return _set_junction(name, id, 'elevation', 'float', str(elevation))
-
-
-def set_junction_demand(name: str, id: str, demand: float) -> ChangeSet:
-    return _set_junction(name, id, 'demand', 'float', str(demand), True)
-
-
-def set_junction_pattern(name: str, id: str, pattern: str) -> ChangeSet:
-    if not is_pattern(name, pattern):
-        return ChangeSet()
-
-    return _set_junction(name, id, 'pattern', 'str', pattern, True)
-
-
-def set_junction_coord(name: str, id: str, x: float, y: float) -> ChangeSet:
-    if not is_junction(name, id):
-        return ChangeSet()
-
-    return set_node_coord(name, JUNCTION, id, x, y)
-
-
-def get_junction_property_names(name: str) -> list[str]:
-    return ['elevation', 'demand', 'pattern', 'coord', 'links']
-
-
-def get_junction_properties(name: str, id: str) -> dict[str, Any] | None:
-    row = _get_junction(name, id)
+def get_junction(name: str, id: str) -> dict[str, Any] | None:
+    row = _query_junction(name, id)
     if row == None:
         return None
 
     ps: dict[str, str] = {}
     ps['elevation'] = float(row['elevation'])
-    ps['demand'] = float(row['demand']) if row != None and row['demand'] != None else None 
-    ps['pattern'] = row['pattern'] if row != None and row['pattern'] != None else None
+    ps['demand'] = float(row['demand']) if row['demand'] != None else None
+    ps['pattern'] = row['pattern']
     ps['coord'] = get_node_coord(name, id)
     ps['links'] = get_node_links(name, id)
     return ps
+
+
+def delete_junction(name: str, id: str) -> ChangeSet:
+    row = get_junction(name, id)
+    if row == None:
+        return ChangeSet()
+
+    old = Serialize(get_junction(name, id), schema).to_storage()
+
+    sql = f"delete from coordinates where node = '{id}';"
+    sql += f"\ndelete from junctions where id = '{id}';"
+    sql += f"\ndelete from _node where id = '{id}';"
+
+    undo = f"insert into _node (id, type) values (''{id}'', ''{JUNCTION}'');"
+    undo += f"\ninsert into junctions (id, elevation, demand, pattern) values (''{id}'', {old['elevation']}, {old['demand']}, {old['pattern']});"
+    undo += f"\ninsert into coordinates (node, coord) values (''{id}'', {old['coord']});"
+
+    write(name, sql)
+    add_operation(name, sql.replace("'", "''"), undo, 'delete_junction', API_DELETE, JUNCTION, id)
+    return get_current_change_set(name)
+
+
+def set_junction(name: str, id: str, properties: dict[str, Any]) -> ChangeSet:
+    if not is_junction(name, id):
+        return ChangeSet()
+
+    old = Serialize(get_junction(name, id), schema).to_storage()
+
+    new = get_junction(name, id)
+    ps: list[str] = []
+    for key in properties:
+        if key in schema and schema[key]['readonly'] == False:
+            new[key] = properties[key]
+            ps.append(key)
+    new = Serialize(new, schema).to_execution()
+
+    sql = f"update junctions set elevation = {new['elevation']}, demand = {new['demand']}, pattern = {new['pattern']} where id = '{id}';"
+    undo = ""
+    if 'coord' in ps:
+        sql += f"\nupdate coordinates set coord = {new['coord']} where node = '{id}';"
+        undo = f"update coordinates set coord = {old['coord']} where node = ''{id}'';"
+    undo += f"\nupdate junctions set elevation = {old['elevation']}, demand = {old['demand']}, pattern = {old['pattern']} where id = ''{id}'';"
+
+    write(name, sql)
+    add_operation(name, sql.replace("'", "''"), undo, 'set_junction', API_UPDATE, JUNCTION, id, ps)
+    return get_current_change_set(name)
diff --git a/tjnetwork.py b/tjnetwork.py
index 2ca8ed2..1939b63 100644
--- a/tjnetwork.py
+++ b/tjnetwork.py
@@ -71,32 +71,23 @@ def copy_project(source: str, new: str) -> None:
 def get_current_operation(name: str) -> int:
     return api.get_current_operation(name)
 
-def undo(name: str) -> None:
-    return api.undo(name)
+def execute_undo(name: str, discard: bool = False) -> ChangeSet:
+    return api.execute_undo(name, discard)
 
-def redo(name: str) -> None:
-    return api.redo(name)
+def execute_redo(name: str) -> ChangeSet:
+    return api.execute_redo(name)
 
 def have_snapshot(name: str, tag: str) -> bool:
     return api.have_snapshot(name, tag)
 
-def take_snapshot(name: str, tag: str) -> None:
+def take_snapshot(name: str, tag: str) -> int:
     return api.take_snapshot(name, tag)
 
-def pick_snapshot(name: str, tag: str) -> None:
-    return api.pick_snapshot(name, tag)
+def pick_snapshot(name: str, tag: str, discard: bool = False) -> ChangeSet:
+    return api.pick_snapshot(name, tag, discard)
 
-def have_transaction(name: str) -> bool:
-    return api.have_transaction(name)
-
-def start_transaction(name: str, strict: bool = False) -> None:
-    return api.start_transaction(name, strict)
-
-def commit_transaction(name: str) -> None:
-    return api.commit_transaction(name)
-
-def abort_transaction(name: str) -> None:
-    return api.abort_transaction(name)
+def sync_with_server(name: str, operation: int) -> ChangeSet:
+    return api.sync_with_server(name, operation)
 
 
 ############################################################
@@ -161,8 +152,8 @@ def get_title(name: str) -> str:
 # junction 2.[JUNCTIONS]
 ############################################################
 
-def get_junction_property_names(name: str) -> list[str]:
-    return api.get_junction_property_names(name)
+def get_junction_schema(name: str) -> dict[str, str]:
+    return api.get_junction_schema(name)
 
 def add_junction(name: str, junction_id: str, x: float, y: float, elevation: float) -> ChangeSet:
     return api.add_junction(name, junction_id, x, y, elevation)
@@ -170,20 +161,11 @@ def add_junction(name: str, junction_id: str, x: float, y: float, elevation: flo
 def delete_junction(name: str, junction_id: str) -> ChangeSet:
     return api.delete_junction(name, junction_id)
 
-def set_junction_elevation(name: str, junction_id: str, elevation: float) -> ChangeSet:
-    return api.set_junction_elevation(name, junction_id, elevation)
+def get_junction(name: str, junction_id: str) -> dict[str, Any] | None:
+    return api.get_junction(name, junction_id)
 
-def set_junction_demand(name: str, junction_id: str, demand: float) -> ChangeSet:
-    return api.set_junction_demand(name, junction_id, demand)
-
-def set_junction_pattern(name: str, junction_id: str, pattern: str) -> ChangeSet:
-    return api.set_junction_pattern(name, junction_id, pattern)
-
-def set_junction_coord(name: str, junction_id: str, x: float, y: float) -> ChangeSet:
-    return api.set_junction_coord(name, junction_id, x, y)
-
-def get_junction_properties(name: str, junction_id: str) -> dict[str, Any] | None:
-    return api.get_junction_properties(name, junction_id)
+def set_junction(name: str, junction_id: str, properties: dict[str, Any]) -> ChangeSet:
+    return api.set_junction(name, junction_id, properties)
 
 
 ############################################################