diff --git a/src/nancy/schema.sql b/src/nancy/schema.sql
index 51390cb..5d28841 100644
--- a/src/nancy/schema.sql
+++ b/src/nancy/schema.sql
@@ -2,56 +2,130 @@
 PRAGMA user_version=0; -- version of this schema.
 -- ^^^^^ Increment the above whenever meaningful updates are made to this file.
 
+
 PRAGMA foreign_keys=ON;
+-- NOTE that ON UPDATE CASCADE is used for all foreign keys, in order to
+-- facilitate easy importing of one database into another
+
+
+-- We track host machines, so that we can give better information about file
+-- locations. This also allows us to see whether platform-dependent behavior may
+-- come into play. Note that these are not reliable identifiers for purposes of
+-- tracking down data, but may be helpful context.
+CREATE TABLE machine(id INTEGER PRIMARY KEY NOT NULL,
+    hostname TEXT, -- platform.node(): 'lucky'
+    processor TEXT, -- platform.processor(): 
+    system TEXT, -- platform.system(): 'Linux'
+    release TEXT, -- platform.release(): '5.15.64'
+    machine TEXT, -- platform.machine(): 'x86_64'
+    timezone TEXT, -- timezone, for interpreting event times
+    freedesktop_os_release TEXT, -- requires python 3.10
+    -- platform.freedesktop_os_release() as JSON
+        -- "{'NAME': 'NixOS', 'ID': 'nixos',
+        -- 'PRETTY_NAME': 'NixOS 22.05 (Quokka)', 'BUG_REPORT_URL':
+        -- 'https://github.com/NixOS/nixpkgs/issues', 'BUILD_ID':
+        -- '22.05.20220902.67e4507', 'DOCUMENTATION_URL':
+        -- 'https://nixos.org/learn.html', 'HOME_URL': 'https://nixos.org/', 'LOGO':
+        -- 'nix-snowflake', 'SUPPORT_URL': 'https://nixos.org/community.html',
+        -- 'VERSION': '22.05 (Quokka)', 'VERSION_CODENAME': 'quokka', 'VERSION_ID':
+        -- '22.05'}"
+    win32_ver TEXT, -- platform.win32_ver() as JSON
+    mac_ver TEXT -- platform.mac_ver() as JSON
+);
+-- Programs are run by users on machines
+CREATE TABLE user(id INTEGER PRIMARY KEY NOT NULL,
+    username TEXT NOT NULL,
+    userid INTEGER,
+    fullname TEXT,
+    machine INTEGER NOT NULL,
+
+    UNIQUE(userid, machine),
+    FOREIGN KEY (machine) REFERENCES machine (id) ON UPDATE CASCADE
+);
+
 
 -- Stores, directories, and files
 -- These are the primary objects tracked by nancy.
--- A store is a directory containing a file called nancy.db
+-- A store is a directory containing a file called nancy.db (e.g. the dir holding this database)
 CREATE TABLE store (id INTEGER PRIMARY KEY NOT NULL,
-    name TEXT,
-    dbpath TEXT NOT NULL
+    machine INTEGER,
+    dbpath TEXT NOT NULL,
+    imported BOOL, -- is this the store for the current directory? If not, then it was
+    -- imported in order to describe a dependency.
+
+    FOREIGN KEY (machine) REFERENCES machine (id) ON UPDATE CASCADE
 );
 -- Within the store are directories that contain files.
+-- Note that there should be one entry with relpath='.' for the non-imported store.
 CREATE TABLE store_directory (id INTEGER PRIMARY KEY NOT NULL,
+    name TEXT,
     store INTEGER NOT NULL,
-    relpath TEXT,
+    parent INTEGER, -- parent directory (should be) in same store
     frozen BOOL NOT NULL,
-    FOREIGN KEY (store) REFERENCES store (id)
+
+    UNIQUE(store, name, parent),
+    FOREIGN KEY (store) REFERENCES store (id) ON UPDATE CASCADE,
+    -- parent is a recursive key within this table.
+    FOREIGN KEY (parent) REFERENCES store_directory (id) ON UPDATE CASCADE
 );
+CREATE TRIGGER insert_store_directory BEFORE INSERT ON store_directory
+BEGIN
+  SELECT
+    CASE
+      WHEN NEW.parent IS NOT NULL AND NEW.store != (SELECT store FROM store_directory WHERE id = NEW.parent) 
+        THEN RAISE (ABORT, 'Parent directory resides in different store')
+    END;
+END;
+CREATE TRIGGER update_store_directory BEFORE UPDATE ON store_directory
+BEGIN
+  SELECT
+    CASE
+      WHEN NEW.parent IS NOT NULL AND NEW.store != (SELECT store FROM store_directory WHERE id = NEW.parent) 
+        THEN RAISE (ABORT, 'Parent directory resides in different store')
+    END;
+END;
+
 CREATE TABLE store_file (id INTEGER PRIMARY KEY NOT NULL,
-    directory INTEGER NOT NULL,
-    relpath TEXT,  -- path relative to top-level of _store_, not dir
+    directory INTEGER NOT NULL,  -- reference a directory inside a store
+    filename TEXT,  -- only a filename, not a path
     frozen BOOL NOT NULL,
+    unfrozen_perms TEXT, -- stat.filemode(os.stat(path).st_mode): '-rw-rw-r--'
 
     source_datum INTEGER,
 
-    FOREIGN KEY (directory) REFERENCES store_directory (id)
-    FOREIGN KEY (source_datum) REFERENCES datum (id)
+    UNIQUE(filename, directory),
+    FOREIGN KEY (directory) REFERENCES store_directory (id) ON UPDATE CASCADE,
+    FOREIGN KEY (source_datum) REFERENCES datum (id) ON UPDATE CASCADE
 );
 
--- computational environment which can execute "runs"
+-- A computational environment which can execute "processes". Note that the
+-- python executable being used, and environment variables are recorded here.
+-- Other info is available in the parent "machine" table.
 CREATE TABLE environment (id INTEGER PRIMARY KEY NOT NULL,
-    hostname TEXT, -- platform.node(): computer's network name
     envvars_json TEXT, -- json.dumps(dict(os.environ))
     python_implementation TEXT, -- platform.python_implementation(): 'cpython'
     python_strversion TEXT, -- sys.version: '3.9.7 (default, Sep 16 2021, 13:09:58) \n[GCC 7.5.0]'
     python_hexversion INTEGER, -- sys.hexversion: 50923504
-    python_host_platform TEXT -- platform.platform(): Linux-5.15.0-46-generic-x86_64-with-glibc2.31
+    user INTEGER,
+
+    FOREIGN KEY (user) REFERENCES user (id) ON UPDATE CASCADE
 );
 
--- A "process" is an execution of a single graph, starting from a number of roots
--- It corresponds to a single host process. Note that if multiple calls to
--- nancy.run() are provided within a single python script, multiple "processes"
--- may be created.  Also note that historical processes are automatically
+-- A "program" is an execution of a single graph, starting from a number of roots
+-- It corresponds to a single host parent process. Note that if multiple calls to
+-- nancy.run() are provided within a single python script, multiple "programs"
+-- may be created.  Also note that historical programs are automatically
 -- imported and merged when possible when loading a "datum" from disk.
-CREATE TABLE process (id INTEGER PRIMARY KEY NOT NULL,
+CREATE TABLE program (id INTEGER PRIMARY KEY NOT NULL,
+    name TEXT,  -- name of the program, usually written in code e.g. cnn_crossval
     -- we use POSIX timestamps in UTC for time recording.
     -- e.g. datetime.datetime.now().timestamp()
     start_time REAL,
     end_time REAL,
     process_id INTEGER,  -- host PID of python process on host OS
     environment INTEGER NOT NULL,
-    FOREIGN KEY (environment) REFERENCES environment (id)
+    message TEXT, -- user-defined message to help distinguish similar runs
+    FOREIGN KEY (environment) REFERENCES environment (id) ON UPDATE CASCADE
 );
 -- We try to track all python packages that impact execution by traversing a
 -- copy of sys.modules. This is done once before a "process" and once after in
@@ -60,7 +134,7 @@ CREATE TABLE py_package (id INTEGER PRIMARY KEY NOT NULL,
     name TEXT NOT NULL,
     version TEXT,
     process INTEGER NOT NULL,
-    FOREIGN KEY (process) REFERENCES process (id)
+    FOREIGN KEY (process) REFERENCES process (id) ON UPDATE CASCADE
 );
 -- A py_module describes any python module file containing decorated Functions.
 -- Modules are tracked since they impact the global scope of function calls.
@@ -68,7 +142,7 @@ CREATE TABLE py_module(id INTEGER PRIMARY KEY NOT NULL,
     name TEXT NOT NULL,
     code TEXT,
     package INTEGER,
-    FOREIGN KEY (package) REFERENCES py_package (id)
+    FOREIGN KEY (package) REFERENCES py_package (id) ON UPDATE CASCADE
 );
 -- A "func" just describes a function, without reference to its arguments. It
 -- can have inputs and outputs, which are described in the func_inputs and
@@ -80,7 +154,7 @@ CREATE TABLE func(id INTEGER PRIMARY KEY NOT NULL,
     -- e.g. datetime.datetime.now().timestamp()
     start_time REAL,
     end_time REAL,
-    FOREIGN KEY (module) REFERENCES py_module (id)
+    FOREIGN KEY (module) REFERENCES py_module (id) ON UPDATE CASCADE
 );
 CREATE TABLE func_input(id INTEGER PRIMARY KEY NOT NULL,
     name TEXT NOT NULL,
@@ -93,7 +167,7 @@ CREATE TABLE func_input(id INTEGER PRIMARY KEY NOT NULL,
 
     description TEXT,
 
-    FOREIGN KEY (func) REFERENCES func (id)
+    FOREIGN KEY (func) REFERENCES func (id) ON UPDATE CASCADE
 );
 CREATE TABLE func_output(id INTEGER PRIMARY KEY NOT NULL,
     name TEXT,
@@ -103,7 +177,7 @@ CREATE TABLE func_output(id INTEGER PRIMARY KEY NOT NULL,
     position INTEGER NOT NULL,
     description TEXT,
 
-    FOREIGN KEY (func) REFERENCES func (id)
+    FOREIGN KEY (func) REFERENCES func (id) ON UPDATE CASCADE
 );
 
 
@@ -114,8 +188,8 @@ CREATE TABLE func_output(id INTEGER PRIMARY KEY NOT NULL,
 CREATE TABLE task(id INTEGER PRIMARY KEY NOT NULL,
     func INTEGER NOT NULL,
     process INTEGER NOT NULL,
-    FOREIGN KEY (func) REFERENCES func (id),
-    FOREIGN KEY (process) REFERENCES process (id)
+    FOREIGN KEY (func) REFERENCES func (id) ON UPDATE CASCADE,
+    FOREIGN KEY (process) REFERENCES process (id) ON UPDATE CASCADE
 );
 -- A datum is an object that is computed as the output of a task, given as a
 -- literal value in a config file, or loaded from a file.
@@ -141,15 +215,15 @@ CREATE TABLE datum(id INTEGER PRIMARY KEY NOT NULL,
     -- hash of provenance summarizes all dependencies, independent of environment
     -- computed _before_ computation
     hash_provenance TEXT,
-    hash_content TEXT, -- hash of content
+    hash_content TEXT, -- hash of content is only computed when this datum is saved to disk
 
     -- Version starts at 0 when provided/first computed. When passed as
     -- a non-const input to a non-const function, this version recorded and
     -- incremented
     current_version INTEGER NOT NULL,
 
-    FOREIGN KEY (task) REFERENCES task (id),
-    FOREIGN KEY (task_output) REFERENCES func_output (id)
+    FOREIGN KEY (task) REFERENCES task (id) ON UPDATE CASCADE,
+    FOREIGN KEY (task_output) REFERENCES func_output (id) ON UPDATE CASCADE
 );
 -- A task input records the version of a Datum that is passed to the function
 CREATE TABLE task_input(id INTEGER PRIMARY KEY NOT NULL,
@@ -161,7 +235,7 @@ CREATE TABLE task_input(id INTEGER PRIMARY KEY NOT NULL,
     -- is passed to a non-const operation, a new datum is provided
     datum_version INTEGER NOT NULL,
 
-    FOREIGN KEY (task) REFERENCES task (id),
-    FOREIGN KEY (func_input) REFERENCES func_input (id),
-    FOREIGN KEY (datum) REFERENCES datum (id)
+    FOREIGN KEY (task) REFERENCES task (id) ON UPDATE CASCADE,
+    FOREIGN KEY (func_input) REFERENCES func_input (id) ON UPDATE CASCADE,
+    FOREIGN KEY (datum) REFERENCES datum (id) ON UPDATE CASCADE
 );
diff --git a/tests/test_db.py b/tests/test_db.py
index a470c91..4911e0d 100644
--- a/tests/test_db.py
+++ b/tests/test_db.py
@@ -1,8 +1,203 @@
-def test_schema_version_match():
-    import nancy
-    from nancy.version import schema_version
+"""
+Pure SQL tests that don't depend on nancy's Python code
+"""
+import pytest
 
-    cur = nancy._conn.cursor()
-    (db_schema_ver,) = cur.execute("PRAGMA user_version;").fetchone()
+import os
+import sqlite3
+
+
+@pytest.fixture
+def db():
+    """Create an in-memory database that follow's the nancy schema"""
+    conn = sqlite3.connect(':memory:')
+    cur = conn.cursor()
+    #import importlib
+    #schema = importlib.resources.open_text("nancy", "schema.sql").read()
+    schema = open(os.path.join(
+            os.path.dirname(__file__),
+            '../src/nancy/schema.sql',
+        ), 'r').read()
+    cur.executescript(schema)
+    yield cur
+    conn.close()
+
+
+@pytest.fixture(autouse=True)
+def insert_machine(db):
+    db.executemany(
+        'INSERT INTO machine VALUES '
+        '(?, ?, ?, ?, ?, ?, ?, ?, ?, ?)',
+        [(
+            None,
+            'lucky', #hostname TEXT, -- platform.node(): 'lucky'
+            '', #processor TEXT, -- platform.processor():
+            'Linux', #system TEXT, -- platform.system(): 'Linux'
+            '5.15.64', #release TEXT, -- platform.release(): '5.15.64'
+            'aarch64', #machine TEXT, -- platform.machine(): 'x86_64'
+            'EDT', #timezone TEXT, -- timezone, for interpreting event times
+            '', #freedesktop_os_release TEXT, -- requires python 3.10
+            '', #win32_ver TEXT, -- platform.win32_ver() as JSON
+            '', #mac_ver TEXT -- platform.mac_ver() as JSON
+        ), (
+            None,
+            'a100', #hostname TEXT, -- platform.node(): 'lucky'
+            '', #processor TEXT, -- platform.processor():
+            'Linux', #system TEXT, -- platform.system(): 'Linux'
+            '5.15.63', #release TEXT, -- platform.release(): '5.15.64'
+            'x86_64', #machine TEXT, -- platform.machine(): 'x86_64'
+            'EST', #timezone TEXT, -- timezone, for interpreting event times
+            '', #freedesktop_os_release TEXT, -- requires python 3.10
+            '', #win32_ver TEXT, -- platform.win32_ver() as JSON
+            '', #mac_ver TEXT -- platform.mac_ver() as JSON
+        )],
+    )
+def test_insert_machine(db):
+    db.execute('SELECT * FROM machine')
+    machines = db.fetchall()
+    assert len(machines) == 2
+
+@pytest.fixture(autouse=True)
+def insert_user(db):
+    db.executemany(
+        'INSERT INTO user VALUES '
+        '(?, ?, ?, ?, ?)',
+        [(
+            None,
+            'jacob', #username TEXT NOT NULL,
+            101, #userid INTEGER,
+            'Jacob Hinkle', #fullname TEXT,
+            1, #machine INTEGER NOT NULL,
+        ), (
+            None,
+            'jacob', #username TEXT NOT NULL,
+            10301, #userid INTEGER,
+            'Jacob Hinkle', #fullname TEXT,
+            2, #machine INTEGER NOT NULL,
+        ), (
+            None,
+            'bob', #username TEXT NOT NULL,
+            2035, #userid INTEGER,
+            'Just Bob', #fullname TEXT,
+            2, #machine INTEGER NOT NULL,
+        )],
+    )
+def test_insert_user(db):
+    db.execute('SELECT * FROM user')
+    users = db.fetchall()
+    assert len(users) == 3
+def test_invalid_user_machine(db):
+    with pytest.raises(sqlite3.IntegrityError):
+        # should fail foreign key constraint
+        db.execute(
+            'INSERT INTO user VALUES '
+            '(?, ?, ?, ?, ?)',
+            (
+                None,
+                'bozo', #username TEXT NOT NULL,
+                100, #userid INTEGER,
+                'Bozo the Clown', #fullname TEXT,
+                3, #machine INTEGER NOT NULL,
+            ),
+        )
+    with pytest.raises(sqlite3.IntegrityError):
+        # should fail uniqueness constraint
+        db.execute(
+            'INSERT INTO user VALUES '
+            '(?, ?, ?, ?, ?)',
+            (
+                None,
+                'jacob', #username TEXT NOT NULL,
+                101, #userid INTEGER,
+                'Bozo the Clown', #fullname TEXT,
+                1, #machine INTEGER NOT NULL,
+            ),
+        )
+
+
+@pytest.fixture(autouse=True)
+def insert_store(db):
+    db.executemany(
+        'INSERT INTO store VALUES '
+        '(?, ?, ?, ?)',
+        [(
+            None,
+            1, #machine INTEGER,
+            '/path/to/first/store', #dbpath TEXT NOT NULL,
+            False, #imported BOOL,
+        ), (
+            None,
+            1, #machine INTEGER,
+            '/path/to/dependencys/store', #dbpath TEXT NOT NULL,
+            True, #imported BOOL,
+        ), (
+            None,
+            2, #machine INTEGER,
+            # same path but on a separate machine
+            '/path/to/first/store', #dbpath TEXT NOT NULL,
+            True, #imported BOOL,
+        )],
+    )
+@pytest.fixture(autouse=True)
+def insert_store_directory(db):
+    db.executemany(
+        'INSERT INTO store_directory VALUES '
+        '(?, ?, ?, ?, ?)',
+        [(
+            None,
+            '.', #name TEXT,
+            1, #store INTEGER NOT NULL,
+            None, #parent INTEGER, -- parent directory (should be) in same store
+            False, #frozen BOOL NOT NULL,
+        ), (
+            None,
+            'foo', #name TEXT,
+            1, #store INTEGER NOT NULL,
+            1, #parent INTEGER, -- parent directory (should be) in same store
+            False, #frozen BOOL NOT NULL,
+        ), (
+            None,
+            '.', #name TEXT,
+            2, #store INTEGER NOT NULL,
+            None, #parent INTEGER, -- parent directory (should be) in same store
+            False, #frozen BOOL NOT NULL,
+        )],
+    )
+
+def test_crossstore_directory_insert(db):
+    with pytest.raises(sqlite3.IntegrityError):
+        # declaring directory as belonging to store 2, but parent's store is 1
+        db.execute(
+            'INSERT INTO store_directory VALUES '
+            '(?, ?, ?, ?, ?)',
+            (
+                None,
+                '.', #name TEXT,
+                2, #store INTEGER NOT NULL,
+                1, #parent INTEGER, -- parent directory (should be) in same store
+                False, #frozen BOOL NOT NULL,
+            ))
+
+
+@pytest.fixture(autouse=True)
+def insert_store_file(db):
+    db.executemany(
+        'INSERT INTO store_file VALUES '
+        '(?, ?, ?, ?, ?, ?)',
+        [(
+            None,
+            1, #directory INTEGER NOT NULL
+            'example.csv', #filename TEXT
+            1, #frozen BOOL NOT NULL
+            '-rw-rw-r--', #unfrozen_perms TEXT
+            None, #source_datum INTEGER,
+        ), (
+            None,
+            2, #directory INTEGER NOT NULL
+            'plots.png', #filename TEXT
+            1, #frozen BOOL NOT NULL
+            '-rw-r--r--', #unfrozen_perms TEXT
+            None, #source_datum INTEGER,
+        )]
+    )
 
-    assert schema_version == db_schema_ver
diff --git a/tests/test_store.py b/tests/test_store.py
new file mode 100644
index 0000000..e25c1ee
--- /dev/null
+++ b/tests/test_store.py
@@ -0,0 +1,19 @@
+import pytest
+
+@pytest.fixture
+def store():
+    from nancy import store
+
+    s = store.Store.init()
+    yield s
+
+
+
+def test_schema_version_match(store):
+    from nancy.version import schema_version
+
+    cur = store.conn.cursor()
+    (db_schema_ver,) = cur.execute("PRAGMA user_version;").fetchone()
+
+    assert schema_version == db_schema_ver
+