diff --git a/script/sql/create/operation.sql b/script/sql/create/operation.sql
index 893cebd..2f105e6 100644
--- a/script/sql/create/operation.sql
+++ b/script/sql/create/operation.sql
@@ -25,4 +25,5 @@ CREATE TABLE SNAPSHOT_OPERATION
 CREATE TABLE TRANSACTION_OPERATION
 (
   ID INTEGER PRIMARY KEY REFERENCES OPERATION(ID)
+, STRICT BOOLEAN NOT NULL DEFAULT FALSE
 );
diff --git a/script/sql/drop/1.title.sql b/script/sql/drop/1.title.sql
index 215ecc6..7ee6d55 100644
--- a/script/sql/drop/1.title.sql
+++ b/script/sql/drop/1.title.sql
@@ -1,3 +1,3 @@
 -- [TITLE]
 
-DROP TABLE TITLE;
+DROP TABLE IF EXISTS TITLE;
diff --git a/script/sql/drop/10.status.sql b/script/sql/drop/10.status.sql
index 970330e..322a72f 100644
--- a/script/sql/drop/10.status.sql
+++ b/script/sql/drop/10.status.sql
@@ -1,13 +1,13 @@
 -- [STATUS]
 
-DROP TABLE STATUS_LINK;
+DROP TABLE IF EXISTS STATUS_LINK;
 
-DROP TABLE STATUS_VALVE;
+DROP TABLE IF EXISTS STATUS_VALVE;
 
-DROP TYPE STATUS_VALVE_STATUS;
+DROP TYPE IF EXISTS STATUS_VALVE_STATUS;
 
-DROP TABLE STATUS_PUMP;
+DROP TABLE IF EXISTS STATUS_PUMP;
 
-DROP TABLE STATUS_PIPE;
+DROP TABLE IF EXISTS STATUS_PIPE;
 
-DROP TYPE STATUS_PIPE_PUMP_STATUS;
+DROP TYPE IF EXISTS STATUS_PIPE_PUMP_STATUS;
diff --git a/script/sql/drop/11.patterns.sql b/script/sql/drop/11.patterns.sql
index 565c67e..fd08d97 100644
--- a/script/sql/drop/11.patterns.sql
+++ b/script/sql/drop/11.patterns.sql
@@ -1,3 +1,3 @@
 -- [PATTERNS]
 
-DROP TABLE PATTERNS;
+DROP TABLE IF EXISTS PATTERNS;
diff --git a/script/sql/drop/12.curves.sql b/script/sql/drop/12.curves.sql
index 9535588..577464e 100644
--- a/script/sql/drop/12.curves.sql
+++ b/script/sql/drop/12.curves.sql
@@ -1,3 +1,3 @@
 -- [CURVES]
 
-DROP TABLE CURVES;
+DROP TABLE IF EXISTS CURVES;
diff --git a/script/sql/drop/13.controls.sql b/script/sql/drop/13.controls.sql
index 5333175..476259d 100644
--- a/script/sql/drop/13.controls.sql
+++ b/script/sql/drop/13.controls.sql
@@ -1,9 +1,9 @@
 -- [CONTROLS]
 
-DROP TABLE CONTROLS_3;
+DROP TABLE IF EXISTS CONTROLS_3;
 
-DROP TABLE CONTROLS_2;
+DROP TABLE IF EXISTS CONTROLS_2;
 
-DROP TABLE CONTROLS_1;
+DROP TABLE IF EXISTS CONTROLS_1;
 
-DROP TYPE CONTROLS_1_PREP;
+DROP TYPE IF EXISTS CONTROLS_1_PREP;
diff --git a/script/sql/drop/14.rules.sql b/script/sql/drop/14.rules.sql
index 7cc4bac..84e4fd8 100644
--- a/script/sql/drop/14.rules.sql
+++ b/script/sql/drop/14.rules.sql
@@ -1,3 +1,3 @@
 -- [RULES]
 
-DROP TABLE RULES;
+DROP TABLE IF EXISTS RULES;
diff --git a/script/sql/drop/15.energy.sql b/script/sql/drop/15.energy.sql
index 1da9af8..5002d5c 100644
--- a/script/sql/drop/15.energy.sql
+++ b/script/sql/drop/15.energy.sql
@@ -1,9 +1,9 @@
 -- [ENERGY]
 
-DROP TABLE ENERGY_DEMAND_CHARGE;
+DROP TABLE IF EXISTS ENERGY_DEMAND_CHARGE;
 
-DROP TABLE ENERGY_PUMP;
+DROP TABLE IF EXISTS ENERGY_PUMP;
 
-DROP TABLE ENERGY_GLOBAL;
+DROP TABLE IF EXISTS ENERGY_GLOBAL;
 
-DROP TYPE ENERGY_PARAM;
+DROP TYPE IF EXISTS ENERGY_PARAM;
diff --git a/script/sql/drop/16.emitters.sql b/script/sql/drop/16.emitters.sql
index 7aa46f8..40a0af8 100644
--- a/script/sql/drop/16.emitters.sql
+++ b/script/sql/drop/16.emitters.sql
@@ -1,3 +1,3 @@
 -- [EMITTERS]
 
-DROP TABLE EMITTERS;
+DROP TABLE IF EXISTS EMITTERS;
diff --git a/script/sql/drop/17.quality.sql b/script/sql/drop/17.quality.sql
index c15ac7d..b72c290 100644
--- a/script/sql/drop/17.quality.sql
+++ b/script/sql/drop/17.quality.sql
@@ -1,3 +1,3 @@
 -- [QUALITY]
 
-DROP TABLE QUALITY;
+DROP TABLE IF EXISTS QUALITY;
diff --git a/script/sql/drop/18.sources.sql b/script/sql/drop/18.sources.sql
index e11b7ea..0402ffe 100644
--- a/script/sql/drop/18.sources.sql
+++ b/script/sql/drop/18.sources.sql
@@ -1,5 +1,5 @@
 -- [SOURCES]
 
-DROP TABLE SOURCES;
+DROP TABLE IF EXISTS SOURCES;
 
-DROP TYPE SOURCES_TYPE;
+DROP TYPE IF EXISTS SOURCES_TYPE;
diff --git a/script/sql/drop/19.reactions.sql b/script/sql/drop/19.reactions.sql
index bcc9dc5..2f6ba5b 100644
--- a/script/sql/drop/19.reactions.sql
+++ b/script/sql/drop/19.reactions.sql
@@ -1,19 +1,19 @@
 -- [REACTIONS]
 
-DROP TABLE REACTIONS_ROUGHNESS_CORRELATION;
+DROP TABLE IF EXISTS REACTIONS_ROUGHNESS_CORRELATION;
 
-DROP TABLE REACTIONS_LIMITING_POTENTIAL;
+DROP TABLE IF EXISTS REACTIONS_LIMITING_POTENTIAL;
 
-DROP TABLE REACTIONS_TANK;
+DROP TABLE IF EXISTS REACTIONS_TANK;
 
-DROP TABLE REACTIONS_PIPE;
+DROP TABLE IF EXISTS REACTIONS_PIPE;
 
-DROP TYPE REACTIONS_PIPE_PARAM;
+DROP TYPE IF EXISTS REACTIONS_PIPE_PARAM;
 
-DROP TABLE REACTIONS_GLOBAL;
+DROP TABLE IF EXISTS REACTIONS_GLOBAL;
 
-DROP TYPE REACTIONS_GLOBAL_PARAM;
+DROP TYPE IF EXISTS REACTIONS_GLOBAL_PARAM;
 
-DROP TABLE REACTIONS_ORDER;
+DROP TABLE IF EXISTS REACTIONS_ORDER;
 
-DROP TYPE REACTIONS_ORDER_PARAM;
+DROP TYPE IF EXISTS REACTIONS_ORDER_PARAM;
diff --git a/script/sql/drop/2.junctions.sql b/script/sql/drop/2.junctions.sql
index 8fc23c4..ef0a609 100644
--- a/script/sql/drop/2.junctions.sql
+++ b/script/sql/drop/2.junctions.sql
@@ -1,3 +1,3 @@
 -- [JUNCTIONS]
 
-DROP TABLE JUNCTIONS;
+DROP TABLE IF EXISTS JUNCTIONS;
diff --git a/script/sql/drop/20.mixing.sql b/script/sql/drop/20.mixing.sql
index 1434859..938d554 100644
--- a/script/sql/drop/20.mixing.sql
+++ b/script/sql/drop/20.mixing.sql
@@ -1,5 +1,5 @@
 -- [MIXING]
 
-DROP TABLE MIXING;
+DROP TABLE IF EXISTS MIXING;
 
-DROP TYPE MIXING_Model;
+DROP TYPE IF EXISTS MIXING_Model;
diff --git a/script/sql/drop/21.times.sql b/script/sql/drop/21.times.sql
index 0d45aed..f051bd7 100644
--- a/script/sql/drop/21.times.sql
+++ b/script/sql/drop/21.times.sql
@@ -1,3 +1,3 @@
 -- [TIMES]
 
-DROP TABLE TIMES;
+DROP TABLE IF EXISTS TIMES;
diff --git a/script/sql/drop/22.report.sql b/script/sql/drop/22.report.sql
index 58dcd51..790684d 100644
--- a/script/sql/drop/22.report.sql
+++ b/script/sql/drop/22.report.sql
@@ -1,3 +1,3 @@
 -- [REPORT]
 
-DROP TABLE REPORT;
+DROP TABLE IF EXISTS REPORT;
diff --git a/script/sql/drop/23.options.sql b/script/sql/drop/23.options.sql
index 69e9714..7cc629a 100644
--- a/script/sql/drop/23.options.sql
+++ b/script/sql/drop/23.options.sql
@@ -1,3 +1,3 @@
 -- [OPTIONS]
 
-DROP TABLE OPTIONS;
+DROP TABLE IF EXISTS OPTIONS;
diff --git a/script/sql/drop/24.coordinates.sql b/script/sql/drop/24.coordinates.sql
index 59f9f45..04d0465 100644
--- a/script/sql/drop/24.coordinates.sql
+++ b/script/sql/drop/24.coordinates.sql
@@ -1,7 +1,7 @@
 -- [COORDINATES]
 
-DROP INDEX COORDINATES_GIST;
+DROP INDEX IF EXISTS COORDINATES_GIST;
 
-DROP INDEX COORDINATES_SPGIST;
+DROP INDEX IF EXISTS COORDINATES_SPGIST;
 
-DROP TABLE COORDINATES;
+DROP TABLE IF EXISTS COORDINATES;
diff --git a/script/sql/drop/25.vertices.sql b/script/sql/drop/25.vertices.sql
index 1352d0d..f74dd3e 100644
--- a/script/sql/drop/25.vertices.sql
+++ b/script/sql/drop/25.vertices.sql
@@ -1,3 +1,3 @@
 -- [VERTICES]
 
-DROP TABLE VERTICES;
+DROP TABLE IF EXISTS VERTICES;
diff --git a/script/sql/drop/26.labels.sql b/script/sql/drop/26.labels.sql
index 70da104..aa1b2b2 100644
--- a/script/sql/drop/26.labels.sql
+++ b/script/sql/drop/26.labels.sql
@@ -1,3 +1,3 @@
 -- [LABELS]
 
-DROP TABLE LABELS;
+DROP TABLE IF EXISTS LABELS;
diff --git a/script/sql/drop/27.backdrop.sql b/script/sql/drop/27.backdrop.sql
index 85f3bf2..408bb85 100644
--- a/script/sql/drop/27.backdrop.sql
+++ b/script/sql/drop/27.backdrop.sql
@@ -1,3 +1,3 @@
 -- [BACKDROP]
 
-DROP TABLE BACKDROP;
+DROP TABLE IF EXISTS BACKDROP;
diff --git a/script/sql/drop/3.reservoirs.sql b/script/sql/drop/3.reservoirs.sql
index 4fd1e46..9864c18 100644
--- a/script/sql/drop/3.reservoirs.sql
+++ b/script/sql/drop/3.reservoirs.sql
@@ -1,3 +1,3 @@
 -- [RESERVOIRS]
 
-DROP TABLE RESERVOIRS;
+DROP TABLE IF EXISTS RESERVOIRS;
diff --git a/script/sql/drop/4.tanks.sql b/script/sql/drop/4.tanks.sql
index f9a4c27..da0487d 100644
--- a/script/sql/drop/4.tanks.sql
+++ b/script/sql/drop/4.tanks.sql
@@ -1,5 +1,5 @@
 -- [TANKS]
 
-DROP TABLE TANKS;
+DROP TABLE IF EXISTS TANKS;
 
-DROP TYPE TANKS_OVERFLOW;
+DROP TYPE IF EXISTS TANKS_OVERFLOW;
diff --git a/script/sql/drop/5.pipes.sql b/script/sql/drop/5.pipes.sql
index e01acd3..1e23612 100644
--- a/script/sql/drop/5.pipes.sql
+++ b/script/sql/drop/5.pipes.sql
@@ -1,5 +1,5 @@
 -- [PIPES]
 
-DROP TABLE PIPES;
+DROP TABLE IF EXISTS PIPES;
 
-DROP TYPE PIPES_STATUS;
+DROP TYPE IF EXISTS PIPES_STATUS;
diff --git a/script/sql/drop/6.pumps.sql b/script/sql/drop/6.pumps.sql
index 2526df6..5ac9656 100644
--- a/script/sql/drop/6.pumps.sql
+++ b/script/sql/drop/6.pumps.sql
@@ -1,11 +1,11 @@
 -- [PUMPS]
 
-DROP TABLE PUMPS_PROPERTY_PATTERN;
+DROP TABLE IF EXISTS PUMPS_PROPERTY_PATTERN;
 
-DROP TABLE PUMPS_PROPERTY_HEAD;
+DROP TABLE IF EXISTS PUMPS_PROPERTY_HEAD;
 
-DROP TABLE PUMPS_PROPERTY_SPEED;
+DROP TABLE IF EXISTS PUMPS_PROPERTY_SPEED;
 
-DROP TABLE PUMPS_PROPERTY_POWER;
+DROP TABLE IF EXISTS PUMPS_PROPERTY_POWER;
 
-DROP TABLE PUMPS;
+DROP TABLE IF EXISTS PUMPS;
diff --git a/script/sql/drop/7.valves.sql b/script/sql/drop/7.valves.sql
index ca001fe..c95b423 100644
--- a/script/sql/drop/7.valves.sql
+++ b/script/sql/drop/7.valves.sql
@@ -1,5 +1,5 @@
 -- [VALVES]
 
-DROP TABLE VALVES;
+DROP TABLE IF EXISTS VALVES;
 
-DROP TYPE VALVES_TYPE;
+DROP TYPE IF EXISTS VALVES_TYPE;
diff --git a/script/sql/drop/8.tags.sql b/script/sql/drop/8.tags.sql
index 78ec688..df8e3d1 100644
--- a/script/sql/drop/8.tags.sql
+++ b/script/sql/drop/8.tags.sql
@@ -1,5 +1,5 @@
 -- [TAGS]
 
-DROP TABLE TAGS_LINK;
+DROP TABLE IF EXISTS TAGS_LINK;
 
-DROP TABLE TAGS_NODE;
+DROP TABLE IF EXISTS TAGS_NODE;
diff --git a/script/sql/drop/9.demands.sql b/script/sql/drop/9.demands.sql
index 7276cca..ebe0209 100644
--- a/script/sql/drop/9.demands.sql
+++ b/script/sql/drop/9.demands.sql
@@ -1,3 +1,3 @@
 -- [DEMANDS]
 
-DROP TABLE DEMANDS;
+DROP TABLE IF EXISTS DEMANDS;
diff --git a/script/sql/drop/operation.sql b/script/sql/drop/operation.sql
index d69ce33..998ee2f 100644
--- a/script/sql/drop/operation.sql
+++ b/script/sql/drop/operation.sql
@@ -1,7 +1,7 @@
-DROP TABLE TRANSACTION_OPERATION;
+DROP TABLE IF EXISTS TRANSACTION_OPERATION;
 
-DROP TABLE SNAPSHOT_OPERATION;
+DROP TABLE IF EXISTS SNAPSHOT_OPERATION;
 
-DROP TABLE CURRENT_OPERATION;
+DROP TABLE IF EXISTS CURRENT_OPERATION;
 
-DROP TABLE OPERATION;
+DROP TABLE IF EXISTS OPERATION;