Implementing time constraints

I have a table to inventory trees, that looks something like this:

CREATE TABLE tree (
     tree_id             SERIAL PRIMARY KEY,
     tree_species_id     INT NOT NULL REFERENCES tree_species,
     tree_location       POINT NOT NULL,
     tree_install_date   DATE NOT NULL,
     tree_removal_date   DATE,
     CHECK (tree_removal_date > tree_install_date)
);

The natural key here is the combination of location and time, which needs 
to be enforced with a trigger function.

Now I have a table recording notes about the tree, something like this:

CREATE TABLE tree_note (
     tree_id     INT REFERENCES tree,
     note_date   DATE,
     note_text   TEXT NOT NULL CHECK(length(note_text) > 0),
     PRIMARY KEY (tree_id, note_date)
);

I need to check that the note_date falls within the tree_install_date 
and tree_removal_date of the tree it references -- another trigger.

And going back to my tree table, I need to update that trigger to ensure 
no note_dates fall outside the tree_install_date and tree_removal_date 
should they be updated.

Add a few more tables, and before long I have a bunch of triggers 
cross-referencing other tables when ever I insert or update a tree.

I've read several back-and-forth discussions arguing whether or 
not stored procedures and triggers in databases are "evil" or "a good 
thing". In this case, since I'm dealing purely with data integrity 
issues (as opposed to business logic), I'm not overly concerned with 
writing these triggers. But as my triggers get 
more complex, it does make me pause a minute to consider my design -- am I 
doing a lot of manual work for something that, if better modeled, _could_ 
be handled natively by the database?

In short, my noob questions are:

-- Are there any standard strategies for dealing with time-related 
integrity constraints like these? Am I basically on the right track here?

-- In general, should the fact that I need to write a bunch of triggers 
to enforce data integrity raise alarms about my schema design?

Any advice/reassurance is appreciated! Thanks.


Karl Nack

Futurity, Inc.
773-506-2007