Document database triggers

doc/WhatsNew

@@ -4,6 +4,8 @@
 
     * Feature CORE-645 and CORE-745
         Database triggers
+      See also:
+        /doc/sql.extensions/README.db_triggers.txt
       Contributor(s):
         Adriano dos Santos Fernandes <adrianosf at uol.com.br>
 

doc/sql.extensions/README.db_triggers.txt

@@ -0,0 +1,57 @@
+------------------
+Database triggers
+------------------
+
+Author:
+	Adriano dos Santos Fernandes <adrianosf@uol.com.br>
+
+Syntax:
+	<database-trigger> ::=
+		{CREATE | RECREATE | CREATE OR ALTER}
+			TRIGGER <name>
+			[ACTIVE | INACTIVE]
+			ON <event>
+			[POSITION <n>]
+		AS
+		BEGIN
+			...
+		END
+
+	<event> ::=
+		  CONNECT
+		| DISCONNECT
+		| TRANSACTION START
+		| TRANSACTION COMMIT
+		| TRANSACTION ROLLBACK
+
+Syntax rules:
+	1) Database triggers type can't be changed.
+
+Events descriptions:
+
+- CONNECT
+	Database connection established
+	A transaction is started
+	Triggers are fired - uncaught exceptions rollbacks the transaction,
+disconnect the attachment and are returned to the client
+	The transaction is committed
+
+- DISCONNECT
+	A transaction is started
+	Triggers are fired - uncaught exceptions rollbacks the transaction,
+disconnect the attachment and are swalloed
+	The transaction is committed
+	The attachment is disconnected
+
+- TRANSACTION START
+	Triggers are fired in the newly created transaction - uncaught
+exceptions are returned to the client and the transaction is not created
+
+- TRANSACTION COMMIT
+	Triggers are fired in the committing transaction - uncaught exceptions
+rollbacks the triggers savepoint, the commit command is aborted and the
+exception is returned to the client
+
+- TRANSACTION ROLLBACK
+	Triggers are fired in the rolling-back transaction - changes done will
+be rolled-back and exceptions are swallowed