How would I implement interprocess communication from Oracle (10g R1) trigger using DBMS_ALERT?
This could be done this way.  I don't like it much as it is not very elegant and looks fragile if unexpected things happen.

--1)Create a table in the user's schema or another new schema if you want separation.

CREATE TABLE DATA_AUDIT
( Primary_key RAW(16) default SYS_GUID() not null,
  Data_id  Number(10),
  Action   VARCHAR2(10),
  Date_created TIMESTAMP(6)DEFAULT CURRENT_TIMESTAMP);
--add foreign key constraint for Data_id to the parent Table
--add check constraint: Action in ('INSERT','UPDATE','DELETE');

--2) create a trigger on the parent table
CREATE OR REPLACE TRIGGER TGR_PARENT_TABLE
 BEFORE INSERT OR UPDATE OR DELETE
 ON PARENT_TABLE
 FOR EACH ROW
 v_action DATA_AUDIT.action%type;
BEGIN

    IF INSERTING THEN
       v_action := 'INSERT';
    ELSIF DELETING THEN
        v_action := 'DELETE';
    ELSIF UPDATING THEN
        v_action := 'UPDATE';
    ELSE
        --raise an error for an unexpected event and log it
        RAISE;
    END IF;
       Insert into DATA_AUDIT(Primary_key,Data_id, Action,Date_created) VALUES
       (SYS_GUID(), :old.Data_id, v_action,CURRENT_TIMESTAMP);
END;

--3) create a trigger on DATA_AUDIT
CREATE OR REPLACE TRIGGER TGR_DATA_AUDIT
 BEFORE INSERT
 ON DATA_AUDIT
 FOR EACH ROW

BEGIN

DBMS_ALERT.SIGNAL(:old.action, :old.data_id);
END;