diff --git a/.github/workflows/main.yaml b/.github/workflows/main.yaml
index e409eecfa..22e855186 100644
--- a/.github/workflows/main.yaml
+++ b/.github/workflows/main.yaml
@@ -34,7 +34,7 @@ jobs:
             environment: py311, py312
     steps:
       - uses: actions/checkout@v4
-      - uses: prefix-dev/setup-pixi@v0.8.10
+      - uses: prefix-dev/setup-pixi@v0.8.13
         with:
           pixi-version: v0.49.0
           cache: true
@@ -62,6 +62,6 @@ jobs:
         shell: bash -el {0}
       - name: Upload coverage reports
         if: runner.os == 'Linux' && matrix.environment == 'py313'
-        uses: codecov/codecov-action@v4
+        uses: codecov/codecov-action@v5
         with:
           token: ${{ secrets.CODECOV_TOKEN }}
diff --git a/pixi.lock b/pixi.lock
index ae80671d3..413b4bde3 100644
--- a/pixi.lock
+++ b/pixi.lock
@@ -16467,8 +16467,8 @@ packages:
   timestamp: 1733367480074
 - pypi: ./
   name: ttsim
-  version: 0.7.1.dev188+g5d736342.d20250724
-  sha256: cefa7a79ac4a812de443db006820c39c6a5375f5f14df80edff5f39c58e7b87a
+  version: 0.7.1.dev202+g87c1768a.d20250724
+  sha256: 1897b27ec932ff5bea5e4d458fadb66c76918bebd5a5473d3420a21e138f0807
   requires_dist:
   - dags>=0.4.1
   - ipywidgets
diff --git a/pyproject.toml b/pyproject.toml
index b577341db..c8b0fe2cc 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -231,6 +231,8 @@ exclude = []
 
 [tool.ruff.lint.per-file-ignores]
 "conftest.py" = ["ANN"]
+# Re-export things for tab-completion explicitly.
+"src/ttsim/__init__.py" = ["PLW0127"]
 # Long lines.
 "src/ttsim/interface_dag_elements/specialized_environment.py" = ["E501"]
 "src/ttsim/interface_dag_elements/fail_if.py" = ["E501"]
diff --git a/src/ttsim/__init__.py b/src/ttsim/__init__.py
index 92e096995..4b9b69827 100644
--- a/src/ttsim/__init__.py
+++ b/src/ttsim/__init__.py
@@ -1,10 +1,20 @@
 from __future__ import annotations
 
-from ttsim._version import __version__, __version_tuple__, version, version_tuple
+try:
+    # Import the version from _version.py which is dynamically created by
+    # setuptools-scm upon installing the project with pip.
+    # Do not put it under version control!
+    from ttsim._version import __version__, __version_tuple__, version, version_tuple
+except ImportError:
+    __version__ = "unknown"
+    __version_tuple__ = ("unknown", "unknown", "unknown")
+    version = "unknown"
+    version_tuple = ("unknown", "unknown", "unknown")
+
+from ttsim import tt
 from ttsim.copy_environment import copy_environment
-from ttsim.interface_dag import main
-from ttsim.interface_dag_elements import MainTarget
-from ttsim.interface_dag_elements.shared import merge_trees
+from ttsim.interface_dag_elements.shared import merge_trees, upsert_tree
+from ttsim.main import main
 from ttsim.main_args import (
     InputData,
     Labels,
@@ -14,6 +24,24 @@
     SpecializedEnvironment,
     TTTargets,
 )
+from ttsim.main_target import MainTarget
+from ttsim.plot_dag import plot_interface_dag, plot_tt_dag
+
+copy_environment = copy_environment
+merge_trees = merge_trees
+upsert_tree = upsert_tree
+main = main
+plot_tt_dag = plot_tt_dag
+plot_interface_dag = plot_interface_dag
+MainTarget = MainTarget
+InputData = InputData
+Labels = Labels
+OrigPolicyObjects = OrigPolicyObjects
+RawResults = RawResults
+Results = Results
+SpecializedEnvironment = SpecializedEnvironment
+TTTargets = TTTargets
+tt = tt
 
 __all__ = [
     "InputData",
@@ -29,6 +57,10 @@
     "copy_environment",
     "main",
     "merge_trees",
+    "plot_interface_dag",
+    "plot_tt_dag",
+    "tt",
+    "upsert_tree",
     "version",
     "version_tuple",
 ]
diff --git a/src/ttsim/copy_environment.py b/src/ttsim/copy_environment.py
index c01740ea8..4117ad8bc 100644
--- a/src/ttsim/copy_environment.py
+++ b/src/ttsim/copy_environment.py
@@ -8,7 +8,7 @@
 import optree
 
 if TYPE_CHECKING:
-    from ttsim.interface_dag_elements.typing import (
+    from ttsim.typing import (
         PolicyEnvironment,
         SpecEnvWithoutTreeLogicAndWithDerivedFunctions,
         SpecEnvWithPartialledParamsAndScalars,
diff --git a/src/ttsim/interface_dag_elements/__init__.py b/src/ttsim/interface_dag_elements/__init__.py
index 398ff7617..e69de29bb 100644
--- a/src/ttsim/interface_dag_elements/__init__.py
+++ b/src/ttsim/interface_dag_elements/__init__.py
@@ -1,172 +0,0 @@
-from __future__ import annotations
-
-from dataclasses import dataclass, field
-from typing import Any
-
-
-@dataclass(frozen=True)
-class MainTargetABC:
-    @classmethod
-    def to_dict(cls) -> dict[str, Any]:
-        return {
-            k: v.to_dict() if isinstance(v, type(MainTargetABC)) else v
-            for k, v in cls.__dict__.items()
-            if not k.startswith("_")
-        }
-
-    def __post_init__(self) -> None:
-        raise NotImplementedError("Do not instantiate this class directly.")
-
-
-@dataclass(frozen=True)
-class WarnIf(MainTargetABC):
-    functions_and_data_columns_overlap: str = (
-        "warn_if__functions_and_data_columns_overlap"
-    )
-    evaluation_date_set_in_multiple_places: str = (
-        "warn_if__evaluation_date_set_in_multiple_places"
-    )
-
-
-@dataclass(frozen=True)
-class FailIf(MainTargetABC):
-    active_periods_overlap: str = "fail_if__active_periods_overlap"
-    any_paths_are_invalid: str = "fail_if__any_paths_are_invalid"
-    backend_has_changed: str = "fail_if__backend_has_changed"
-    environment_is_invalid: str = "fail_if__environment_is_invalid"
-    foreign_keys_are_invalid_in_data: str = "fail_if__foreign_keys_are_invalid_in_data"
-    group_ids_are_outside_top_level_namespace: str = (
-        "fail_if__group_ids_are_outside_top_level_namespace"
-    )
-    group_variables_are_not_constant_within_groups: str = (
-        "fail_if__group_variables_are_not_constant_within_groups"
-    )
-    input_data_is_invalid: str = "fail_if__input_data_is_invalid"
-    input_data_tree_is_invalid: str = "fail_if__input_data_tree_is_invalid"
-    input_df_has_bool_or_numeric_column_names: str = (
-        "fail_if__input_df_has_bool_or_numeric_column_names"
-    )
-    input_df_mapper_columns_missing_in_df: str = (
-        "fail_if__input_df_mapper_columns_missing_in_df"
-    )
-    input_df_mapper_has_incorrect_format: str = (
-        "fail_if__input_df_mapper_has_incorrect_format"
-    )
-    non_convertible_objects_in_results_tree: str = (
-        "fail_if__non_convertible_objects_in_results_tree"
-    )
-    param_function_depends_on_column_objects: str = (
-        "fail_if__param_function_depends_on_column_objects"
-    )
-    paths_are_missing_in_targets_tree_mapper: str = (
-        "fail_if__paths_are_missing_in_targets_tree_mapper"
-    )
-    tt_root_nodes_are_missing: str = "fail_if__tt_root_nodes_are_missing"
-    targets_are_not_in_specialized_environment_or_data: str = (
-        "fail_if__targets_are_not_in_specialized_environment_or_data"
-    )
-    targets_tree_is_invalid: str = "fail_if__targets_tree_is_invalid"
-
-
-@dataclass(frozen=True)
-class Results(MainTargetABC):
-    df_with_mapper: str = "results__df_with_mapper"
-    df_with_nested_columns: str = "results__df_with_nested_columns"
-    tree: str = "results__tree"
-
-
-@dataclass(frozen=True)
-class RawResults(MainTargetABC):
-    columns: str = "raw_results__columns"
-    combined: str = "raw_results__combined"
-    from_input_data: str = "raw_results__from_input_data"
-    params: str = "raw_results__params"
-
-
-@dataclass(frozen=True)
-class SpecializedEnvironment(MainTargetABC):
-    without_tree_logic_and_with_derived_functions: str = (
-        "specialized_environment__without_tree_logic_and_with_derived_functions"
-    )
-    with_processed_params_and_scalars: str = (
-        "specialized_environment__with_processed_params_and_scalars"
-    )
-    with_partialled_params_and_scalars: str = (
-        "specialized_environment__with_partialled_params_and_scalars"
-    )
-    tax_transfer_dag: str = "specialized_environment__tax_transfer_dag"
-    tax_transfer_function: str = "specialized_environment__tax_transfer_function"
-
-
-@dataclass(frozen=True)
-class Targets(MainTargetABC):
-    qname: str = "tt_targets__qname"
-    tree: str = "tt_targets__tree"
-
-
-@dataclass(frozen=True)
-class Labels(MainTargetABC):
-    column_targets: str = "labels__column_targets"
-    grouping_levels: str = "labels__grouping_levels"
-    input_data_targets: str = "labels__input_data_targets"
-    param_targets: str = "labels__param_targets"
-    processed_data_columns: str = "labels__processed_data_columns"
-    input_columns: str = "labels__input_columns"
-    root_nodes: str = "labels__root_nodes"
-    top_level_namespace: str = "labels__top_level_namespace"
-
-
-@dataclass(frozen=True)
-class DfAndMapper(MainTargetABC):
-    df: str = "input_data__df_and_mapper__df"
-    mapper: str = "input_data__df_and_mapper__mapper"
-
-
-@dataclass(frozen=True)
-class InputData(MainTargetABC):
-    df_and_mapper: type[DfAndMapper] = field(default=DfAndMapper)
-    df_with_nested_columns: str = "input_data__df_with_nested_columns"
-    flat: str = "input_data__flat"
-    tree: str = "input_data__tree"
-
-
-@dataclass(frozen=True)
-class OrigPolicyObjects(MainTargetABC):
-    column_objects_and_param_functions: str = (
-        "orig_policy_objects__column_objects_and_param_functions"
-    )
-    param_specs: str = "orig_policy_objects__param_specs"
-    # Do not include root here, will be pre-defined in user-facing implementations.
-
-
-@dataclass(frozen=True)
-class Templates(MainTargetABC):
-    input_data_dtypes: str = "templates__input_data_dtypes"
-
-
-@dataclass(frozen=True)
-class MainTarget(MainTargetABC):
-    results: type[Results] = field(default=Results)
-    templates: type[Templates] = field(default=Templates)
-    policy_environment: str = "policy_environment"
-    specialized_environment: type[SpecializedEnvironment] = field(
-        default=SpecializedEnvironment
-    )
-    orig_policy_objects: type[OrigPolicyObjects] = field(default=OrigPolicyObjects)
-    processed_data: str = "processed_data"
-    raw_results: type[RawResults] = field(default=RawResults)
-    labels: type[Labels] = field(default=Labels)
-    input_data: type[InputData] = field(default=InputData)
-    tt_targets: type[Targets] = field(default=Targets)
-    num_segments: str = "num_segments"
-    backend: str = "backend"
-    evaluation_date_str: str = "evaluation_date_str"
-    evaluation_date: str = "evaluation_date"
-    policy_date_str: str = "policy_date_str"
-    policy_date: str = "policy_date"
-    xnp: str = "xnp"
-    dnp: str = "dnp"
-    rounding: str = "rounding"
-    tt_function_set_annotations: str = "tt_function_set_annotations"
-    warn_if: type[WarnIf] = field(default=WarnIf)
-    fail_if: type[FailIf] = field(default=FailIf)
diff --git a/src/ttsim/interface_dag_elements/automatically_added_functions.py b/src/ttsim/interface_dag_elements/automatically_added_functions.py
index 4b60bc6d6..8b9f12912 100644
--- a/src/ttsim/interface_dag_elements/automatically_added_functions.py
+++ b/src/ttsim/interface_dag_elements/automatically_added_functions.py
@@ -12,8 +12,8 @@
     get_re_pattern_for_specific_time_units_and_groupings,
     group_pattern,
 )
-from ttsim.tt_dag_elements.aggregation import grouped_sum
-from ttsim.tt_dag_elements.column_objects_param_function import (
+from ttsim.tt.aggregation import grouped_sum
+from ttsim.tt.column_objects_param_function import (
     DEFAULT_END_DATE,
     DEFAULT_START_DATE,
     AggByGroupFunction,
@@ -22,13 +22,13 @@
     ParamFunction,
     TimeConversionFunction,
 )
-from ttsim.tt_dag_elements.param_objects import ScalarParam
+from ttsim.tt.param_objects import ScalarParam
 
 if TYPE_CHECKING:
     import re
     from collections.abc import Callable
 
-    from ttsim.interface_dag_elements.typing import (
+    from ttsim.typing import (
         BoolColumn,
         FloatColumn,
         IntColumn,
@@ -584,7 +584,7 @@ def func(x: BoolColumn) -> FloatColumn: ...
     def func(x: FloatColumn | IntColumn | BoolColumn) -> FloatColumn:
         return converter(x)
 
-    return func  # type: ignore[has-type]
+    return func
 
 
 def create_agg_by_group_functions(
diff --git a/src/ttsim/interface_dag_elements/data_converters.py b/src/ttsim/interface_dag_elements/data_converters.py
index a16a58726..3cdcbdef3 100644
--- a/src/ttsim/interface_dag_elements/data_converters.py
+++ b/src/ttsim/interface_dag_elements/data_converters.py
@@ -8,7 +8,7 @@
 if TYPE_CHECKING:
     from types import ModuleType
 
-    from ttsim.interface_dag_elements.typing import (
+    from ttsim.typing import (
         FlatData,
         NestedData,
         NestedInputsMapper,
diff --git a/src/ttsim/interface_dag_elements/dates.py b/src/ttsim/interface_dag_elements/dates.py
index 2e83d81b1..99166e2a9 100644
--- a/src/ttsim/interface_dag_elements/dates.py
+++ b/src/ttsim/interface_dag_elements/dates.py
@@ -12,7 +12,7 @@
 if TYPE_CHECKING:
     import datetime
 
-    from ttsim.interface_dag_elements.typing import DashedISOString
+    from ttsim.typing import DashedISOString
 
 
 @interface_input(in_top_level_namespace=True)
diff --git a/src/ttsim/interface_dag_elements/fail_if.py b/src/ttsim/interface_dag_elements/fail_if.py
index a74143260..7b3040940 100644
--- a/src/ttsim/interface_dag_elements/fail_if.py
+++ b/src/ttsim/interface_dag_elements/fail_if.py
@@ -23,7 +23,7 @@
 
 from ttsim.interface_dag_elements.interface_node_objects import fail_function
 from ttsim.interface_dag_elements.shared import get_name_of_group_by_id
-from ttsim.tt_dag_elements.column_objects_param_function import (
+from ttsim.tt.column_objects_param_function import (
     DEFAULT_END_DATE,
     ColumnFunction,
     ColumnObject,
@@ -31,7 +31,7 @@
     ParamFunction,
     PolicyInput,
 )
-from ttsim.tt_dag_elements.param_objects import (
+from ttsim.tt.param_objects import (
     PLACEHOLDER_FIELD,
     PLACEHOLDER_VALUE,
     ParamObject,
@@ -41,7 +41,7 @@
     from collections.abc import Callable
 
     from ttsim.interface_dag_elements.input_data import FlatData
-    from ttsim.interface_dag_elements.typing import (
+    from ttsim.typing import (
         FlatColumnObjectsParamFunctions,
         FlatOrigParamSpecs,
         NestedData,
diff --git a/src/ttsim/interface_dag_elements/input_data.py b/src/ttsim/interface_dag_elements/input_data.py
index adbcd44ef..2fdb6b680 100644
--- a/src/ttsim/interface_dag_elements/input_data.py
+++ b/src/ttsim/interface_dag_elements/input_data.py
@@ -18,7 +18,7 @@
 
     import pandas as pd
 
-    from ttsim.interface_dag_elements.typing import (
+    from ttsim.typing import (
         FlatData,
         NestedData,
         NestedInputsMapper,
diff --git a/src/ttsim/interface_dag_elements/interface_node_objects.py b/src/ttsim/interface_dag_elements/interface_node_objects.py
index af64c5862..00a3dd749 100644
--- a/src/ttsim/interface_dag_elements/interface_node_objects.py
+++ b/src/ttsim/interface_dag_elements/interface_node_objects.py
@@ -9,7 +9,7 @@
 if TYPE_CHECKING:
     from collections.abc import Callable, Iterable
 
-    from ttsim.interface_dag_elements.typing import UnorderedQNames
+    from ttsim.typing import UnorderedQNames
 
 
 FunArgTypes = ParamSpec("FunArgTypes")
diff --git a/src/ttsim/interface_dag_elements/labels.py b/src/ttsim/interface_dag_elements/labels.py
index 3d0480b4c..023551c2d 100644
--- a/src/ttsim/interface_dag_elements/labels.py
+++ b/src/ttsim/interface_dag_elements/labels.py
@@ -14,10 +14,10 @@
     get_re_pattern_for_all_time_units_and_groupings,
     group_pattern,
 )
-from ttsim.tt_dag_elements.column_objects_param_function import PolicyInput
+from ttsim.tt.column_objects_param_function import PolicyInput
 
 if TYPE_CHECKING:
-    from ttsim.interface_dag_elements.typing import (
+    from ttsim.typing import (
         OrderedQNames,
         PolicyEnvironment,
         QNameData,
diff --git a/src/ttsim/interface_dag_elements/num_segments.py b/src/ttsim/interface_dag_elements/num_segments.py
index f96f0dade..52b57e1f5 100644
--- a/src/ttsim/interface_dag_elements/num_segments.py
+++ b/src/ttsim/interface_dag_elements/num_segments.py
@@ -5,7 +5,7 @@
 from ttsim.interface_dag_elements.interface_node_objects import interface_function
 
 if TYPE_CHECKING:
-    from ttsim.interface_dag_elements.typing import QNameData
+    from ttsim.typing import QNameData
 
 
 @interface_function(in_top_level_namespace=True)
diff --git a/src/ttsim/interface_dag_elements/orig_policy_objects.py b/src/ttsim/interface_dag_elements/orig_policy_objects.py
index 9e225e761..b17204802 100644
--- a/src/ttsim/interface_dag_elements/orig_policy_objects.py
+++ b/src/ttsim/interface_dag_elements/orig_policy_objects.py
@@ -11,7 +11,7 @@
     interface_function,
     interface_input,
 )
-from ttsim.tt_dag_elements.column_objects_param_function import (
+from ttsim.tt.column_objects_param_function import (
     ColumnObject,
     ParamFunction,
 )
@@ -20,7 +20,7 @@
     from pathlib import Path
     from types import ModuleType
 
-    from ttsim.interface_dag_elements.typing import (
+    from ttsim.typing import (
         FlatColumnObjectsParamFunctions,
         FlatOrigParamSpecs,
         OrigParamSpec,
diff --git a/src/ttsim/interface_dag_elements/policy_environment.py b/src/ttsim/interface_dag_elements/policy_environment.py
index 114faa77a..c91fe4e5b 100644
--- a/src/ttsim/interface_dag_elements/policy_environment.py
+++ b/src/ttsim/interface_dag_elements/policy_environment.py
@@ -12,7 +12,7 @@
     merge_trees,
     upsert_tree,
 )
-from ttsim.tt_dag_elements import (
+from ttsim.tt import (
     ConsecutiveIntLookupTableParam,
     DictParam,
     ParamObject,
@@ -24,15 +24,15 @@
     get_month_based_phase_inout_of_age_thresholds_param_value,
     get_year_based_phase_inout_of_age_thresholds_param_value,
 )
-from ttsim.tt_dag_elements.column_objects_param_function import (
+from ttsim.tt.column_objects_param_function import (
     DEFAULT_END_DATE,
 )
-from ttsim.tt_dag_elements.piecewise_polynomial import get_piecewise_parameters
+from ttsim.tt.piecewise_polynomial import get_piecewise_parameters
 
 if TYPE_CHECKING:
     from types import ModuleType
 
-    from ttsim.interface_dag_elements.typing import (
+    from ttsim.typing import (
         FlatColumnObjectsParamFunctions,
         FlatOrigParamSpecs,
         NestedColumnObjectsParamFunctions,
diff --git a/src/ttsim/interface_dag_elements/processed_data.py b/src/ttsim/interface_dag_elements/processed_data.py
index 9ec206063..5bdbb7185 100644
--- a/src/ttsim/interface_dag_elements/processed_data.py
+++ b/src/ttsim/interface_dag_elements/processed_data.py
@@ -5,12 +5,12 @@
 import dags.tree as dt
 
 from ttsim.interface_dag_elements.interface_node_objects import interface_function
-from ttsim.tt_dag_elements.column_objects_param_function import reorder_ids
+from ttsim.tt.column_objects_param_function import reorder_ids
 
 if TYPE_CHECKING:
     from types import ModuleType
 
-    from ttsim.interface_dag_elements.typing import FlatData, QNameData
+    from ttsim.typing import FlatData, QNameData
 
 
 @interface_function(in_top_level_namespace=True)
diff --git a/src/ttsim/interface_dag_elements/raw_results.py b/src/ttsim/interface_dag_elements/raw_results.py
index a841b84ab..882c1384d 100644
--- a/src/ttsim/interface_dag_elements/raw_results.py
+++ b/src/ttsim/interface_dag_elements/raw_results.py
@@ -7,7 +7,7 @@
 if TYPE_CHECKING:
     from collections.abc import Callable
 
-    from ttsim.interface_dag_elements.typing import (
+    from ttsim.typing import (
         OrderedQNames,
         QNameData,
         SpecEnvWithProcessedParamsAndScalars,
diff --git a/src/ttsim/interface_dag_elements/results.py b/src/ttsim/interface_dag_elements/results.py
index b4ebb7ee0..c98cc162a 100644
--- a/src/ttsim/interface_dag_elements/results.py
+++ b/src/ttsim/interface_dag_elements/results.py
@@ -13,7 +13,7 @@
 if TYPE_CHECKING:
     import pandas as pd
 
-    from ttsim.interface_dag_elements.typing import (
+    from ttsim.typing import (
         FlatData,
         NestedData,
         NestedStrings,
diff --git a/src/ttsim/interface_dag_elements/shared.py b/src/ttsim/interface_dag_elements/shared.py
index 1f319ae13..39b59ebff 100644
--- a/src/ttsim/interface_dag_elements/shared.py
+++ b/src/ttsim/interface_dag_elements/shared.py
@@ -8,7 +8,7 @@
 import optree
 
 if TYPE_CHECKING:
-    from ttsim.interface_dag_elements.typing import (
+    from ttsim.typing import (
         DashedISOString,
         NestedColumnObjectsParamFunctions,
         NestedData,
diff --git a/src/ttsim/interface_dag_elements/specialized_environment.py b/src/ttsim/interface_dag_elements/specialized_environment.py
index dc60787ca..8953bf825 100644
--- a/src/ttsim/interface_dag_elements/specialized_environment.py
+++ b/src/ttsim/interface_dag_elements/specialized_environment.py
@@ -15,13 +15,13 @@
     interface_input,
 )
 from ttsim.interface_dag_elements.shared import merge_trees
-from ttsim.tt_dag_elements.column_objects_param_function import (
+from ttsim.tt.column_objects_param_function import (
     ColumnFunction,
     ColumnObject,
     ParamFunction,
     PolicyInput,
 )
-from ttsim.tt_dag_elements.param_objects import ParamObject, RawParam
+from ttsim.tt.param_objects import ParamObject, RawParam
 
 if TYPE_CHECKING:
     import datetime
@@ -30,7 +30,7 @@
 
     import networkx as nx
 
-    from ttsim.interface_dag_elements.typing import (
+    from ttsim.typing import (
         OrderedQNames,
         PolicyEnvironment,
         QNameData,
diff --git a/src/ttsim/interface_dag_elements/templates.py b/src/ttsim/interface_dag_elements/templates.py
index 1afad2303..afc2a15d6 100644
--- a/src/ttsim/interface_dag_elements/templates.py
+++ b/src/ttsim/interface_dag_elements/templates.py
@@ -9,11 +9,11 @@
 from ttsim.interface_dag_elements.shared import (
     get_re_pattern_for_all_time_units_and_groupings,
 )
-from ttsim.tt_dag_elements.column_objects_param_function import PolicyInput
-from ttsim.tt_dag_elements.vectorization import scalar_type_to_array_type
+from ttsim.tt.column_objects_param_function import PolicyInput
+from ttsim.tt.vectorization import scalar_type_to_array_type
 
 if TYPE_CHECKING:
-    from ttsim.interface_dag_elements.typing import (
+    from ttsim.typing import (
         NestedInputStructureDict,
         OrderedQNames,
         PolicyEnvironment,
diff --git a/src/ttsim/interface_dag_elements/tt_targets.py b/src/ttsim/interface_dag_elements/tt_targets.py
index 667ed883f..9621d491b 100644
--- a/src/ttsim/interface_dag_elements/tt_targets.py
+++ b/src/ttsim/interface_dag_elements/tt_targets.py
@@ -7,10 +7,10 @@
 from ttsim.interface_dag_elements.interface_node_objects import (
     interface_function,
 )
-from ttsim.tt_dag_elements.column_objects_param_function import ColumnFunction
+from ttsim.tt.column_objects_param_function import ColumnFunction
 
 if TYPE_CHECKING:
-    from ttsim.interface_dag_elements.typing import (
+    from ttsim.typing import (
         NestedStrings,
         NestedTargetDict,
         OrderedQNames,
diff --git a/src/ttsim/interface_dag_elements/warn_if.py b/src/ttsim/interface_dag_elements/warn_if.py
index 1c07cfca7..28f94b267 100644
--- a/src/ttsim/interface_dag_elements/warn_if.py
+++ b/src/ttsim/interface_dag_elements/warn_if.py
@@ -10,12 +10,12 @@
     format_list_linewise,
 )
 from ttsim.interface_dag_elements.interface_node_objects import warn_function
-from ttsim.tt_dag_elements.column_objects_param_function import PolicyInput
+from ttsim.tt.column_objects_param_function import PolicyInput
 
 if TYPE_CHECKING:
     import datetime
 
-    from ttsim.interface_dag_elements.typing import (
+    from ttsim.typing import (
         PolicyEnvironment,
         QNameData,
         UnorderedQNames,
diff --git a/src/ttsim/interface_dag.py b/src/ttsim/main.py
similarity index 99%
rename from src/ttsim/interface_dag.py
rename to src/ttsim/main.py
index 3653526d9..a118b5b5a 100644
--- a/src/ttsim/interface_dag.py
+++ b/src/ttsim/main.py
@@ -11,7 +11,6 @@
 import networkx as nx
 import optree
 
-from ttsim.interface_dag_elements import MainTarget, MainTargetABC
 from ttsim.interface_dag_elements.fail_if import (
     format_errors_and_warnings,
     format_list_linewise,
@@ -25,19 +24,12 @@
 )
 from ttsim.interface_dag_elements.orig_policy_objects import load_module
 from ttsim.main_args import MainArg
+from ttsim.main_target import MainTarget, MainTargetABC
 
 if TYPE_CHECKING:
     import datetime
     from collections.abc import Iterable
 
-    from ttsim.interface_dag_elements.typing import (
-        DashedISOString,
-        FlatInterfaceObjects,
-        NestedTargetDict,
-        PolicyEnvironment,
-        QNameData,
-        UnorderedQNames,
-    )
     from ttsim.main_args import (
         InputData,
         Labels,
@@ -47,6 +39,14 @@
         SpecializedEnvironment,
         TTTargets,
     )
+    from ttsim.typing import (
+        DashedISOString,
+        FlatInterfaceObjects,
+        NestedTargetDict,
+        PolicyEnvironment,
+        QNameData,
+        UnorderedQNames,
+    )
 
 
 def main(
diff --git a/src/ttsim/main_args.py b/src/ttsim/main_args.py
index f07063d76..ab273fae7 100644
--- a/src/ttsim/main_args.py
+++ b/src/ttsim/main_args.py
@@ -10,7 +10,7 @@
     import networkx as nx
     import pandas as pd
 
-    from ttsim.interface_dag_elements.typing import (
+    from ttsim.typing import (
         FlatColumnObjectsParamFunctions,
         FlatData,
         FlatOrigParamSpecs,
diff --git a/src/ttsim/main_target.py b/src/ttsim/main_target.py
new file mode 100644
index 000000000..398ff7617
--- /dev/null
+++ b/src/ttsim/main_target.py
@@ -0,0 +1,172 @@
+from __future__ import annotations
+
+from dataclasses import dataclass, field
+from typing import Any
+
+
+@dataclass(frozen=True)
+class MainTargetABC:
+    @classmethod
+    def to_dict(cls) -> dict[str, Any]:
+        return {
+            k: v.to_dict() if isinstance(v, type(MainTargetABC)) else v
+            for k, v in cls.__dict__.items()
+            if not k.startswith("_")
+        }
+
+    def __post_init__(self) -> None:
+        raise NotImplementedError("Do not instantiate this class directly.")
+
+
+@dataclass(frozen=True)
+class WarnIf(MainTargetABC):
+    functions_and_data_columns_overlap: str = (
+        "warn_if__functions_and_data_columns_overlap"
+    )
+    evaluation_date_set_in_multiple_places: str = (
+        "warn_if__evaluation_date_set_in_multiple_places"
+    )
+
+
+@dataclass(frozen=True)
+class FailIf(MainTargetABC):
+    active_periods_overlap: str = "fail_if__active_periods_overlap"
+    any_paths_are_invalid: str = "fail_if__any_paths_are_invalid"
+    backend_has_changed: str = "fail_if__backend_has_changed"
+    environment_is_invalid: str = "fail_if__environment_is_invalid"
+    foreign_keys_are_invalid_in_data: str = "fail_if__foreign_keys_are_invalid_in_data"
+    group_ids_are_outside_top_level_namespace: str = (
+        "fail_if__group_ids_are_outside_top_level_namespace"
+    )
+    group_variables_are_not_constant_within_groups: str = (
+        "fail_if__group_variables_are_not_constant_within_groups"
+    )
+    input_data_is_invalid: str = "fail_if__input_data_is_invalid"
+    input_data_tree_is_invalid: str = "fail_if__input_data_tree_is_invalid"
+    input_df_has_bool_or_numeric_column_names: str = (
+        "fail_if__input_df_has_bool_or_numeric_column_names"
+    )
+    input_df_mapper_columns_missing_in_df: str = (
+        "fail_if__input_df_mapper_columns_missing_in_df"
+    )
+    input_df_mapper_has_incorrect_format: str = (
+        "fail_if__input_df_mapper_has_incorrect_format"
+    )
+    non_convertible_objects_in_results_tree: str = (
+        "fail_if__non_convertible_objects_in_results_tree"
+    )
+    param_function_depends_on_column_objects: str = (
+        "fail_if__param_function_depends_on_column_objects"
+    )
+    paths_are_missing_in_targets_tree_mapper: str = (
+        "fail_if__paths_are_missing_in_targets_tree_mapper"
+    )
+    tt_root_nodes_are_missing: str = "fail_if__tt_root_nodes_are_missing"
+    targets_are_not_in_specialized_environment_or_data: str = (
+        "fail_if__targets_are_not_in_specialized_environment_or_data"
+    )
+    targets_tree_is_invalid: str = "fail_if__targets_tree_is_invalid"
+
+
+@dataclass(frozen=True)
+class Results(MainTargetABC):
+    df_with_mapper: str = "results__df_with_mapper"
+    df_with_nested_columns: str = "results__df_with_nested_columns"
+    tree: str = "results__tree"
+
+
+@dataclass(frozen=True)
+class RawResults(MainTargetABC):
+    columns: str = "raw_results__columns"
+    combined: str = "raw_results__combined"
+    from_input_data: str = "raw_results__from_input_data"
+    params: str = "raw_results__params"
+
+
+@dataclass(frozen=True)
+class SpecializedEnvironment(MainTargetABC):
+    without_tree_logic_and_with_derived_functions: str = (
+        "specialized_environment__without_tree_logic_and_with_derived_functions"
+    )
+    with_processed_params_and_scalars: str = (
+        "specialized_environment__with_processed_params_and_scalars"
+    )
+    with_partialled_params_and_scalars: str = (
+        "specialized_environment__with_partialled_params_and_scalars"
+    )
+    tax_transfer_dag: str = "specialized_environment__tax_transfer_dag"
+    tax_transfer_function: str = "specialized_environment__tax_transfer_function"
+
+
+@dataclass(frozen=True)
+class Targets(MainTargetABC):
+    qname: str = "tt_targets__qname"
+    tree: str = "tt_targets__tree"
+
+
+@dataclass(frozen=True)
+class Labels(MainTargetABC):
+    column_targets: str = "labels__column_targets"
+    grouping_levels: str = "labels__grouping_levels"
+    input_data_targets: str = "labels__input_data_targets"
+    param_targets: str = "labels__param_targets"
+    processed_data_columns: str = "labels__processed_data_columns"
+    input_columns: str = "labels__input_columns"
+    root_nodes: str = "labels__root_nodes"
+    top_level_namespace: str = "labels__top_level_namespace"
+
+
+@dataclass(frozen=True)
+class DfAndMapper(MainTargetABC):
+    df: str = "input_data__df_and_mapper__df"
+    mapper: str = "input_data__df_and_mapper__mapper"
+
+
+@dataclass(frozen=True)
+class InputData(MainTargetABC):
+    df_and_mapper: type[DfAndMapper] = field(default=DfAndMapper)
+    df_with_nested_columns: str = "input_data__df_with_nested_columns"
+    flat: str = "input_data__flat"
+    tree: str = "input_data__tree"
+
+
+@dataclass(frozen=True)
+class OrigPolicyObjects(MainTargetABC):
+    column_objects_and_param_functions: str = (
+        "orig_policy_objects__column_objects_and_param_functions"
+    )
+    param_specs: str = "orig_policy_objects__param_specs"
+    # Do not include root here, will be pre-defined in user-facing implementations.
+
+
+@dataclass(frozen=True)
+class Templates(MainTargetABC):
+    input_data_dtypes: str = "templates__input_data_dtypes"
+
+
+@dataclass(frozen=True)
+class MainTarget(MainTargetABC):
+    results: type[Results] = field(default=Results)
+    templates: type[Templates] = field(default=Templates)
+    policy_environment: str = "policy_environment"
+    specialized_environment: type[SpecializedEnvironment] = field(
+        default=SpecializedEnvironment
+    )
+    orig_policy_objects: type[OrigPolicyObjects] = field(default=OrigPolicyObjects)
+    processed_data: str = "processed_data"
+    raw_results: type[RawResults] = field(default=RawResults)
+    labels: type[Labels] = field(default=Labels)
+    input_data: type[InputData] = field(default=InputData)
+    tt_targets: type[Targets] = field(default=Targets)
+    num_segments: str = "num_segments"
+    backend: str = "backend"
+    evaluation_date_str: str = "evaluation_date_str"
+    evaluation_date: str = "evaluation_date"
+    policy_date_str: str = "policy_date_str"
+    policy_date: str = "policy_date"
+    xnp: str = "xnp"
+    dnp: str = "dnp"
+    rounding: str = "rounding"
+    tt_function_set_annotations: str = "tt_function_set_annotations"
+    warn_if: type[WarnIf] = field(default=WarnIf)
+    fail_if: type[FailIf] = field(default=FailIf)
diff --git a/src/ttsim/plot_dag.py b/src/ttsim/plot_dag.py
index af4f2a0e8..e755385d5 100644
--- a/src/ttsim/plot_dag.py
+++ b/src/ttsim/plot_dag.py
@@ -14,7 +14,6 @@
 import plotly.graph_objects as go
 
 from ttsim import main
-from ttsim.interface_dag import load_flat_interface_functions_and_inputs
 from ttsim.interface_dag_elements.interface_node_objects import (
     FailFunction,
     InputDependentInterfaceFunction,
@@ -23,7 +22,8 @@
     WarnFunction,
     interface_function,
 )
-from ttsim.tt_dag_elements import (
+from ttsim.main import load_flat_interface_functions_and_inputs
+from ttsim.tt import (
     ColumnFunction,
     ParamFunction,
     ParamObject,
@@ -38,7 +38,7 @@
     from pathlib import Path
     from types import ModuleType
 
-    from ttsim.interface_dag_elements.typing import (
+    from ttsim.typing import (
         PolicyEnvironment,
         SpecEnvWithoutTreeLogicAndWithDerivedFunctions,
     )
@@ -150,6 +150,7 @@ def plot_interface_dag(
     include_fail_and_warn_nodes: bool = True,
     show_node_description: bool = False,
     output_path: Path | None = None,
+    remove_orig_policy_objects__root: bool = True,
 ) -> go.Figure:
     """Plot the full interface DAG."""
     interface_functions_and_inputs = load_flat_interface_functions_and_inputs()
@@ -194,6 +195,8 @@ def plot_interface_dag(
             description=description or "No description available.",
             namespace=namespace,
         )
+    if remove_orig_policy_objects__root:
+        dag.remove_nodes_from(["orig_policy_objects__root"])
 
     fig = _plot_dag(
         dag=dag,
diff --git a/src/ttsim/testing_utils.py b/src/ttsim/testing_utils.py
index a71971220..788a2b006 100644
--- a/src/ttsim/testing_utils.py
+++ b/src/ttsim/testing_utils.py
@@ -17,7 +17,7 @@
 from ttsim.interface_dag_elements.fail_if import format_list_linewise
 from ttsim.interface_dag_elements.shared import to_datetime
 from ttsim.plot_dag import dummy_callable
-from ttsim.tt_dag_elements.column_objects_param_function import PolicyInput
+from ttsim.tt.column_objects_param_function import PolicyInput
 
 # Set display options to show all columns without truncation
 pd.set_option("display.max_columns", None)
@@ -28,7 +28,7 @@
     from pathlib import Path
     from types import ModuleType
 
-    from ttsim.interface_dag_elements.typing import (
+    from ttsim.typing import (
         FlatColumnObjectsParamFunctions,
         FlatOrigParamSpecs,
         NestedData,
diff --git a/src/ttsim/tt_dag_elements/__init__.py b/src/ttsim/tt/__init__.py
similarity index 83%
rename from src/ttsim/tt_dag_elements/__init__.py
rename to src/ttsim/tt/__init__.py
index e8a1a3b53..07daf9636 100644
--- a/src/ttsim/tt_dag_elements/__init__.py
+++ b/src/ttsim/tt/__init__.py
@@ -1,5 +1,5 @@
-from ttsim.tt_dag_elements.aggregation import AggType
-from ttsim.tt_dag_elements.column_objects_param_function import (
+from ttsim.tt.aggregation import AggType
+from ttsim.tt.column_objects_param_function import (
     AggByGroupFunction,
     AggByPIDFunction,
     ColumnFunction,
@@ -17,7 +17,7 @@
     policy_function,
     policy_input,
 )
-from ttsim.tt_dag_elements.param_objects import (
+from ttsim.tt.param_objects import (
     ConsecutiveIntLookupTableParam,
     ConsecutiveIntLookupTableParamValue,
     DictParam,
@@ -30,12 +30,13 @@
     get_month_based_phase_inout_of_age_thresholds_param_value,
     get_year_based_phase_inout_of_age_thresholds_param_value,
 )
-from ttsim.tt_dag_elements.piecewise_polynomial import (
+from ttsim.tt.piecewise_polynomial import (
     get_piecewise_parameters,
+    get_piecewise_thresholds,
     piecewise_polynomial,
 )
-from ttsim.tt_dag_elements.rounding import RoundingSpec
-from ttsim.tt_dag_elements.shared import join
+from ttsim.tt.rounding import RoundingSpec
+from ttsim.tt.shared import join
 
 __all__ = [
     "AggByGroupFunction",
@@ -63,6 +64,7 @@
     "get_consecutive_int_lookup_table_param_value",
     "get_month_based_phase_inout_of_age_thresholds_param_value",
     "get_piecewise_parameters",
+    "get_piecewise_thresholds",
     "get_year_based_phase_inout_of_age_thresholds_param_value",
     "group_creation_function",
     "join",
diff --git a/src/ttsim/tt_dag_elements/aggregation.py b/src/ttsim/tt/aggregation.py
similarity index 98%
rename from src/ttsim/tt_dag_elements/aggregation.py
rename to src/ttsim/tt/aggregation.py
index 20fb25f84..86f7798fb 100644
--- a/src/ttsim/tt_dag_elements/aggregation.py
+++ b/src/ttsim/tt/aggregation.py
@@ -3,10 +3,10 @@
 from enum import StrEnum
 from typing import TYPE_CHECKING, Literal, overload
 
-from ttsim.tt_dag_elements import aggregation_jax, aggregation_numpy
+from ttsim.tt import aggregation_jax, aggregation_numpy
 
 if TYPE_CHECKING:
-    from ttsim.tt_dag_elements.typing import BoolColumn, FloatColumn, IntColumn
+    from ttsim.tt import BoolColumn, FloatColumn, IntColumn
 
 
 class AggType(StrEnum):
diff --git a/src/ttsim/tt_dag_elements/aggregation_jax.py b/src/ttsim/tt/aggregation_jax.py
similarity index 98%
rename from src/ttsim/tt_dag_elements/aggregation_jax.py
rename to src/ttsim/tt/aggregation_jax.py
index ff0566fea..696434650 100644
--- a/src/ttsim/tt_dag_elements/aggregation_jax.py
+++ b/src/ttsim/tt/aggregation_jax.py
@@ -9,7 +9,7 @@
     pass
 
 if TYPE_CHECKING:
-    from ttsim.tt_dag_elements.typing import BoolColumn, FloatColumn, IntColumn
+    from ttsim.tt import BoolColumn, FloatColumn, IntColumn
 
 
 def grouped_count(group_id: IntColumn, num_segments: int) -> jnp.ndarray:
diff --git a/src/ttsim/tt_dag_elements/aggregation_numpy.py b/src/ttsim/tt/aggregation_numpy.py
similarity index 99%
rename from src/ttsim/tt_dag_elements/aggregation_numpy.py
rename to src/ttsim/tt/aggregation_numpy.py
index 31afc2ba1..c1cdce1a2 100644
--- a/src/ttsim/tt_dag_elements/aggregation_numpy.py
+++ b/src/ttsim/tt/aggregation_numpy.py
@@ -6,7 +6,7 @@
 import numpy_groupies as npg
 
 if TYPE_CHECKING:
-    from ttsim.tt_dag_elements.typing import BoolColumn, FloatColumn, IntColumn
+    from ttsim.tt import BoolColumn, FloatColumn, IntColumn
 
 
 def grouped_count(group_id: IntColumn) -> IntColumn:
diff --git a/src/ttsim/tt_dag_elements/column_objects_param_function.py b/src/ttsim/tt/column_objects_param_function.py
similarity index 99%
rename from src/ttsim/tt_dag_elements/column_objects_param_function.py
rename to src/ttsim/tt/column_objects_param_function.py
index c5321aa8c..95991d28f 100644
--- a/src/ttsim/tt_dag_elements/column_objects_param_function.py
+++ b/src/ttsim/tt/column_objects_param_function.py
@@ -11,7 +11,7 @@
 from dags import rename_arguments
 
 from ttsim.interface_dag_elements.shared import to_datetime
-from ttsim.tt_dag_elements.aggregation import (
+from ttsim.tt.aggregation import (
     AggType,
     all_by_p_id,
     any_by_p_id,
@@ -28,14 +28,14 @@
     min_by_p_id,
     sum_by_p_id,
 )
-from ttsim.tt_dag_elements.rounding import RoundingSpec
-from ttsim.tt_dag_elements.vectorization import vectorize_function
+from ttsim.tt.rounding import RoundingSpec
+from ttsim.tt.vectorization import vectorize_function
 
 if TYPE_CHECKING:
     from collections.abc import Callable
     from types import ModuleType
 
-    from ttsim.interface_dag_elements.typing import (
+    from ttsim.typing import (
         DashedISOString,
         IntColumn,
         UnorderedQNames,
diff --git a/src/ttsim/tt_dag_elements/param_objects.py b/src/ttsim/tt/param_objects.py
similarity index 99%
rename from src/ttsim/tt_dag_elements/param_objects.py
rename to src/ttsim/tt/param_objects.py
index 00f0e306e..b0ef9bbd8 100644
--- a/src/ttsim/tt_dag_elements/param_objects.py
+++ b/src/ttsim/tt/param_objects.py
@@ -12,7 +12,7 @@
 
     from jaxtyping import Array, Bool, Float, Int
 
-    from ttsim.tt_dag_elements.typing import NestedLookupDict
+    from ttsim.typing import NestedLookupDict
 
 
 @dataclass(frozen=True)
diff --git a/src/ttsim/tt_dag_elements/piecewise_polynomial.py b/src/ttsim/tt/piecewise_polynomial.py
similarity index 98%
rename from src/ttsim/tt_dag_elements/piecewise_polynomial.py
rename to src/ttsim/tt/piecewise_polynomial.py
index 879d594c7..36e6948f4 100644
--- a/src/ttsim/tt_dag_elements/piecewise_polynomial.py
+++ b/src/ttsim/tt/piecewise_polynomial.py
@@ -5,7 +5,7 @@
 
 import numpy
 
-from ttsim.tt_dag_elements.param_objects import PiecewisePolynomialParamValue
+from ttsim.tt.param_objects import PiecewisePolynomialParamValue
 
 if TYPE_CHECKING:
     from types import ModuleType
@@ -122,7 +122,7 @@ def get_piecewise_parameters(
         )
 
     # Extract lower thresholds.
-    lower_thresholds, upper_thresholds, thresholds = check_and_get_thresholds(
+    lower_thresholds, upper_thresholds, thresholds = get_piecewise_thresholds(
         leaf_name=leaf_name,
         parameter_dict=parameter_dict,
         xnp=xnp,
@@ -151,7 +151,7 @@ def get_piecewise_parameters(
     )
 
 
-def check_and_get_thresholds(  # noqa: C901
+def get_piecewise_thresholds(  # noqa: C901
     leaf_name: str,
     parameter_dict: dict[int, dict[str, float]],
     xnp: ModuleType,
diff --git a/src/ttsim/tt_dag_elements/rounding.py b/src/ttsim/tt/rounding.py
similarity index 97%
rename from src/ttsim/tt_dag_elements/rounding.py
rename to src/ttsim/tt/rounding.py
index 1a9e6cd80..ecb7ce1c0 100644
--- a/src/ttsim/tt_dag_elements/rounding.py
+++ b/src/ttsim/tt/rounding.py
@@ -8,7 +8,7 @@
     from collections.abc import Callable
     from types import ModuleType
 
-    from ttsim.interface_dag_elements.typing import FloatColumn
+    from ttsim.typing import FloatColumn
 
 
 ROUNDING_DIRECTION = Literal["up", "down", "nearest"]
diff --git a/src/ttsim/tt_dag_elements/shared.py b/src/ttsim/tt/shared.py
similarity index 96%
rename from src/ttsim/tt_dag_elements/shared.py
rename to src/ttsim/tt/shared.py
index 833760041..b2d18255f 100644
--- a/src/ttsim/tt_dag_elements/shared.py
+++ b/src/ttsim/tt/shared.py
@@ -5,7 +5,7 @@
 if TYPE_CHECKING:
     from types import ModuleType
 
-    from ttsim.interface_dag_elements.typing import BoolColumn, FloatColumn, IntColumn
+    from ttsim.typing import BoolColumn, FloatColumn, IntColumn
 
 
 @overload
diff --git a/src/ttsim/tt_dag_elements/vectorization.py b/src/ttsim/tt/vectorization.py
similarity index 100%
rename from src/ttsim/tt_dag_elements/vectorization.py
rename to src/ttsim/tt/vectorization.py
diff --git a/src/ttsim/tt_dag_elements/typing.py b/src/ttsim/tt_dag_elements/typing.py
deleted file mode 100644
index 66486f5ad..000000000
--- a/src/ttsim/tt_dag_elements/typing.py
+++ /dev/null
@@ -1,20 +0,0 @@
-from __future__ import annotations
-
-from typing import TYPE_CHECKING, Any, Literal, NewType, TypeAlias
-
-if TYPE_CHECKING:
-    import datetime
-
-    NestedLookupDict: TypeAlias = dict[int, float | int | bool | "NestedLookupDict"]
-    OrigParamSpec = (
-        # Header
-        dict[str, str | None | dict[Literal["de", "en"], str | None]]
-        |
-        # Parameters at one point in time
-        dict[
-            datetime.date,
-            dict[Literal["note", "reference"] | str | int, Any],  # noqa: PYI051
-        ]
-    )
-    DashedISOString = NewType("DashedISOString", str)
-    """A string representing a date in the format 'YYYY-MM-DD'."""
diff --git a/src/ttsim/interface_dag_elements/typing.py b/src/ttsim/typing.py
similarity index 93%
rename from src/ttsim/interface_dag_elements/typing.py
rename to src/ttsim/typing.py
index 1b07fdd7e..107b0d51f 100644
--- a/src/ttsim/interface_dag_elements/typing.py
+++ b/src/ttsim/typing.py
@@ -2,14 +2,13 @@
 
 from typing import TYPE_CHECKING, Any, Literal, NewType, TypeAlias, TypeVar
 
-from jaxtyping import Array, Bool, Float, Int
-
-BoolColumn: TypeAlias = Bool[Array, " n_obs"]
-IntColumn: TypeAlias = Int[Array, " n_obs"]
-FloatColumn: TypeAlias = Float[Array, " n_obs"]
+if TYPE_CHECKING:
+    from jaxtyping import Array, Bool, Float, Int
 
+    BoolColumn: TypeAlias = Bool[Array, " n_obs"]
+    IntColumn: TypeAlias = Int[Array, " n_obs"]
+    FloatColumn: TypeAlias = Float[Array, " n_obs"]
 
-if TYPE_CHECKING:
     # Make these available for import from other modules.
     import datetime
     from collections.abc import Iterable, Mapping
@@ -45,7 +44,7 @@
     # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # #
     # Possible leaves of the various trees.
     # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # #
-    from ttsim.tt_dag_elements import (
+    from ttsim.tt import (
         ColumnFunction,
         ColumnObject,
         ParamFunction,
@@ -112,3 +111,5 @@
     """Map qualified names to column objects and anything that comes out of processing the params."""  # noqa: E501
     SpecEnvWithPartialledParamsAndScalars = Mapping[str, ColumnFunction]
     """Map qualified names to column functions that depend on columns only."""
+
+    NestedLookupDict: TypeAlias = dict[int, float | int | bool | "NestedLookupDict"]
diff --git a/tests/interface_dag_elements/test_automatically_added_functions.py b/tests/interface_dag_elements/test_automatically_added_functions.py
index 3952f3149..bac513254 100644
--- a/tests/interface_dag_elements/test_automatically_added_functions.py
+++ b/tests/interface_dag_elements/test_automatically_added_functions.py
@@ -29,7 +29,7 @@
     y_to_q,
     y_to_w,
 )
-from ttsim.tt_dag_elements import policy_function
+from ttsim.tt import policy_function
 
 
 def return_one() -> int:
diff --git a/tests/interface_dag_elements/test_data_converters.py b/tests/interface_dag_elements/test_data_converters.py
index 88f66a408..fee93fe97 100644
--- a/tests/interface_dag_elements/test_data_converters.py
+++ b/tests/interface_dag_elements/test_data_converters.py
@@ -15,7 +15,7 @@
     df_with_nested_columns_to_flat_data,
     nested_data_to_df_with_mapped_columns,
 )
-from ttsim.tt_dag_elements import (
+from ttsim.tt import (
     ScalarParam,
     param_function,
     policy_function,
diff --git a/tests/interface_dag_elements/test_failures.py b/tests/interface_dag_elements/test_failures.py
index 3f4a6a56b..c52a019c0 100644
--- a/tests/interface_dag_elements/test_failures.py
+++ b/tests/interface_dag_elements/test_failures.py
@@ -35,7 +35,7 @@
     paths_are_missing_in_targets_tree_mapper,
     targets_are_not_in_specialized_environment_or_data,
 )
-from ttsim.tt_dag_elements import (
+from ttsim.tt import (
     ConsecutiveIntLookupTableParam,
     ConsecutiveIntLookupTableParamValue,
     DictParam,
@@ -52,7 +52,7 @@
 
     from jaxtyping import Array, Float
 
-    from ttsim.interface_dag_elements.typing import (
+    from ttsim.typing import (
         FlatColumnObjectsParamFunctions,
         FlatOrigParamSpecs,
         OrigParamSpec,
diff --git a/tests/interface_dag_elements/test_labels.py b/tests/interface_dag_elements/test_labels.py
index 4dd629929..6e43b094b 100644
--- a/tests/interface_dag_elements/test_labels.py
+++ b/tests/interface_dag_elements/test_labels.py
@@ -3,7 +3,7 @@
 import pytest
 
 from ttsim.interface_dag_elements.labels import grouping_levels, top_level_namespace
-from ttsim.tt_dag_elements import policy_function, policy_input
+from ttsim.tt import policy_function, policy_input
 
 
 def identity(x: int) -> int:
diff --git a/tests/interface_dag_elements/test_orig_policy_objects.py b/tests/interface_dag_elements/test_orig_policy_objects.py
index fcb4475fc..3d36f44b9 100644
--- a/tests/interface_dag_elements/test_orig_policy_objects.py
+++ b/tests/interface_dag_elements/test_orig_policy_objects.py
@@ -8,7 +8,7 @@
     _find_files_recursively,
     load_module,
 )
-from ttsim.tt_dag_elements.param_objects import (
+from ttsim.tt.param_objects import (
     ConsecutiveIntLookupTableParam,
     DictParam,
     PiecewisePolynomialParam,
diff --git a/tests/interface_dag_elements/test_policy_environment.py b/tests/interface_dag_elements/test_policy_environment.py
index 71241355c..da9b8dc71 100644
--- a/tests/interface_dag_elements/test_policy_environment.py
+++ b/tests/interface_dag_elements/test_policy_environment.py
@@ -19,12 +19,12 @@
     _active_param_objects,
     _get_param_value,
 )
-from ttsim.tt_dag_elements import ScalarParam, policy_function
+from ttsim.tt import ScalarParam, policy_function
 
 if TYPE_CHECKING:
     from types import ModuleType
 
-    from ttsim.interface_dag_elements.typing import (
+    from ttsim.typing import (
         NestedColumnObjectsParamFunctions,
     )
 
diff --git a/tests/interface_dag_elements/test_specialized_environment.py b/tests/interface_dag_elements/test_specialized_environment.py
index 97740fe76..11e74115a 100644
--- a/tests/interface_dag_elements/test_specialized_environment.py
+++ b/tests/interface_dag_elements/test_specialized_environment.py
@@ -15,7 +15,7 @@
     with_partialled_params_and_scalars,
     with_processed_params_and_scalars,
 )
-from ttsim.tt_dag_elements import (
+from ttsim.tt import (
     AggType,
     DictParam,
     PiecewisePolynomialParam,
@@ -30,7 +30,7 @@
 )
 
 if TYPE_CHECKING:
-    from ttsim.interface_dag_elements.typing import (
+    from ttsim.typing import (
         FloatColumn,
         IntColumn,
         PolicyEnvironment,
diff --git a/tests/interface_dag_elements/test_templates.py b/tests/interface_dag_elements/test_templates.py
index 6e1ae43cf..0658ada19 100644
--- a/tests/interface_dag_elements/test_templates.py
+++ b/tests/interface_dag_elements/test_templates.py
@@ -8,11 +8,11 @@
 from ttsim.testing_utils import (
     load_policy_test_data,
 )
-from ttsim.tt_dag_elements.column_objects_param_function import (
+from ttsim.tt.column_objects_param_function import (
     policy_function,
     policy_input,
 )
-from ttsim.tt_dag_elements.param_objects import DictParam, ScalarParam
+from ttsim.tt.param_objects import DictParam, ScalarParam
 
 METTSIM_ROOT = Path(__file__).parent.parent / "mettsim"
 
diff --git a/tests/interface_dag_elements/test_warnings.py b/tests/interface_dag_elements/test_warnings.py
index 0b930cad6..5481a6d45 100644
--- a/tests/interface_dag_elements/test_warnings.py
+++ b/tests/interface_dag_elements/test_warnings.py
@@ -7,9 +7,9 @@
 import pytest
 
 from ttsim import main
-from ttsim.interface_dag_elements import MainTarget
-from ttsim.tt_dag_elements.column_objects_param_function import policy_function
-from ttsim.tt_dag_elements.param_objects import ScalarParam
+from ttsim.main_target import MainTarget
+from ttsim.tt.column_objects_param_function import policy_function
+from ttsim.tt.param_objects import ScalarParam
 
 
 @policy_function()
diff --git a/tests/mettsim/demographics.py b/tests/mettsim/demographics.py
index 3955bb9d5..1705c02a1 100644
--- a/tests/mettsim/demographics.py
+++ b/tests/mettsim/demographics.py
@@ -1,6 +1,6 @@
 from __future__ import annotations
 
-from ttsim.tt_dag_elements import AggType, agg_by_group_function
+from ttsim.tt import AggType, agg_by_group_function
 
 
 @agg_by_group_function(agg_type=AggType.COUNT)
diff --git a/tests/mettsim/group_by_ids.py b/tests/mettsim/group_by_ids.py
index 0fd158f49..e9b3d55bd 100644
--- a/tests/mettsim/group_by_ids.py
+++ b/tests/mettsim/group_by_ids.py
@@ -2,12 +2,12 @@
 
 from typing import TYPE_CHECKING
 
-from ttsim.tt_dag_elements import group_creation_function
+from ttsim.tt import group_creation_function
 
 if TYPE_CHECKING:
     from types import ModuleType
 
-    from ttsim.interface_dag_elements.typing import IntColumn
+    from ttsim.tt import IntColumn
 
 
 @group_creation_function()
diff --git a/tests/mettsim/housing_benefits/amount.py b/tests/mettsim/housing_benefits/amount.py
index 81a74c29e..43368b9a4 100644
--- a/tests/mettsim/housing_benefits/amount.py
+++ b/tests/mettsim/housing_benefits/amount.py
@@ -1,6 +1,6 @@
 from __future__ import annotations
 
-from ttsim.tt_dag_elements import policy_function
+from ttsim.tt import policy_function
 
 
 @policy_function(vectorization_strategy="vectorize")
diff --git a/tests/mettsim/housing_benefits/eligibility/eligibility.py b/tests/mettsim/housing_benefits/eligibility/eligibility.py
index 3c7919e5f..8abbd9dc7 100644
--- a/tests/mettsim/housing_benefits/eligibility/eligibility.py
+++ b/tests/mettsim/housing_benefits/eligibility/eligibility.py
@@ -11,7 +11,7 @@
 
 from __future__ import annotations
 
-from ttsim.tt_dag_elements import (
+from ttsim.tt import (
     AggType,
     agg_by_group_function,
     policy_function,
diff --git a/tests/mettsim/housing_benefits/income/income.py b/tests/mettsim/housing_benefits/income/income.py
index 6edc2dad1..e73397a47 100644
--- a/tests/mettsim/housing_benefits/income/income.py
+++ b/tests/mettsim/housing_benefits/income/income.py
@@ -1,6 +1,6 @@
 from __future__ import annotations
 
-from ttsim.tt_dag_elements import RoundingSpec, policy_function
+from ttsim.tt import RoundingSpec, policy_function
 
 
 @policy_function(
diff --git a/tests/mettsim/inputs.py b/tests/mettsim/inputs.py
index dd32cd939..058affe31 100644
--- a/tests/mettsim/inputs.py
+++ b/tests/mettsim/inputs.py
@@ -1,6 +1,6 @@
 from __future__ import annotations
 
-from ttsim.tt_dag_elements import AggType, FKType, agg_by_group_function, policy_input
+from ttsim.tt import AggType, FKType, agg_by_group_function, policy_input
 
 
 @policy_input()
diff --git a/tests/mettsim/orc_hunting_bounty/orc_hunting_bounty.py b/tests/mettsim/orc_hunting_bounty/orc_hunting_bounty.py
index 7039d2bd0..642b1381a 100644
--- a/tests/mettsim/orc_hunting_bounty/orc_hunting_bounty.py
+++ b/tests/mettsim/orc_hunting_bounty/orc_hunting_bounty.py
@@ -3,10 +3,10 @@
 from dataclasses import dataclass
 from typing import TYPE_CHECKING
 
-from ttsim.tt_dag_elements import param_function, policy_function, policy_input
+from ttsim.tt import param_function, policy_function, policy_input
 
 if TYPE_CHECKING:
-    from ttsim.interface_dag_elements.typing import RawParam
+    from ttsim.typing import RawParam
 
 
 @dataclass(frozen=True)
diff --git a/tests/mettsim/payroll_tax/amount.py b/tests/mettsim/payroll_tax/amount.py
index f8b5fd11e..dd368f73d 100644
--- a/tests/mettsim/payroll_tax/amount.py
+++ b/tests/mettsim/payroll_tax/amount.py
@@ -5,7 +5,7 @@
 if TYPE_CHECKING:
     from types import ModuleType
 
-from ttsim.tt_dag_elements import (
+from ttsim.tt import (
     PiecewisePolynomialParamValue,
     piecewise_polynomial,
     policy_function,
diff --git a/tests/mettsim/payroll_tax/child_tax_credit/child_tax_credit.py b/tests/mettsim/payroll_tax/child_tax_credit/child_tax_credit.py
index 0d5e55997..14de99b22 100644
--- a/tests/mettsim/payroll_tax/child_tax_credit/child_tax_credit.py
+++ b/tests/mettsim/payroll_tax/child_tax_credit/child_tax_credit.py
@@ -2,7 +2,7 @@
 
 from typing import TYPE_CHECKING
 
-from ttsim.tt_dag_elements import (
+from ttsim.tt import (
     AggType,
     agg_by_p_id_function,
     join,
@@ -12,7 +12,7 @@
 if TYPE_CHECKING:
     from types import ModuleType
 
-    from ttsim.interface_dag_elements.typing import BoolColumn, IntColumn
+    from ttsim.typing import BoolColumn, IntColumn
 
 
 @agg_by_p_id_function(agg_type=AggType.SUM)
diff --git a/tests/mettsim/payroll_tax/child_tax_credit/inputs.py b/tests/mettsim/payroll_tax/child_tax_credit/inputs.py
index f93d891b4..f166f7d5f 100644
--- a/tests/mettsim/payroll_tax/child_tax_credit/inputs.py
+++ b/tests/mettsim/payroll_tax/child_tax_credit/inputs.py
@@ -1,6 +1,6 @@
 from __future__ import annotations
 
-from ttsim.tt_dag_elements import FKType, policy_input
+from ttsim.tt import FKType, policy_input
 
 
 @policy_input(foreign_key_type=FKType.MAY_POINT_TO_SELF)
diff --git a/tests/mettsim/payroll_tax/income/amount.py b/tests/mettsim/payroll_tax/income/amount.py
index 652a41c33..c51dec082 100644
--- a/tests/mettsim/payroll_tax/income/amount.py
+++ b/tests/mettsim/payroll_tax/income/amount.py
@@ -1,6 +1,6 @@
 from __future__ import annotations
 
-from ttsim.tt_dag_elements import policy_function
+from ttsim.tt import policy_function
 
 
 @policy_function(vectorization_strategy="vectorize")
diff --git a/tests/mettsim/payroll_tax/income/deductions.py b/tests/mettsim/payroll_tax/income/deductions.py
index 601c01c7b..6a4a0e388 100644
--- a/tests/mettsim/payroll_tax/income/deductions.py
+++ b/tests/mettsim/payroll_tax/income/deductions.py
@@ -1,6 +1,6 @@
 from __future__ import annotations
 
-from ttsim.tt_dag_elements import policy_function
+from ttsim.tt import policy_function
 
 
 @policy_function(vectorization_strategy="vectorize")
diff --git a/tests/mettsim/payroll_tax/income/inputs.py b/tests/mettsim/payroll_tax/income/inputs.py
index 7ea02d6b2..403f1fe48 100644
--- a/tests/mettsim/payroll_tax/income/inputs.py
+++ b/tests/mettsim/payroll_tax/income/inputs.py
@@ -2,7 +2,7 @@
 
 from __future__ import annotations
 
-from ttsim.tt_dag_elements import policy_input
+from ttsim.tt import policy_input
 
 
 @policy_input()
diff --git a/tests/mettsim/property_tax/amount.py b/tests/mettsim/property_tax/amount.py
index 44d5eaf03..734e0b518 100644
--- a/tests/mettsim/property_tax/amount.py
+++ b/tests/mettsim/property_tax/amount.py
@@ -13,7 +13,7 @@
 if TYPE_CHECKING:
     from types import ModuleType
 
-from ttsim.tt_dag_elements import (
+from ttsim.tt import (
     PiecewisePolynomialParamValue,
     piecewise_polynomial,
     policy_function,
diff --git a/tests/mettsim_tests/test_mettsim.py b/tests/mettsim_tests/test_mettsim.py
index 4c993fd04..99f261b2d 100644
--- a/tests/mettsim_tests/test_mettsim.py
+++ b/tests/mettsim_tests/test_mettsim.py
@@ -22,7 +22,7 @@
 if TYPE_CHECKING:
     import datetime
 
-    from ttsim.interface_dag_elements.typing import (
+    from ttsim.typing import (
         FlatColumnObjectsParamFunctions,
         FlatOrigParamSpecs,
     )
diff --git a/tests/test_copy_environment.py b/tests/test_copy_environment.py
index 48520c51f..540dc4451 100644
--- a/tests/test_copy_environment.py
+++ b/tests/test_copy_environment.py
@@ -8,11 +8,11 @@
 import pytest
 
 from ttsim import copy_environment, main
-from ttsim.interface_dag_elements import MainTarget
-from ttsim.tt_dag_elements.param_objects import RawParam, ScalarParam
+from ttsim.main_target import MainTarget
+from ttsim.tt.param_objects import RawParam, ScalarParam
 
 if TYPE_CHECKING:
-    from ttsim.interface_dag_elements.typing import PolicyEnvironment
+    from ttsim.typing import PolicyEnvironment
 
 
 METTSIM_ROOT = Path(__file__).parent / "mettsim"
diff --git a/tests/test_end_to_end.py b/tests/test_end_to_end.py
index e426835e2..67d6ab69d 100644
--- a/tests/test_end_to_end.py
+++ b/tests/test_end_to_end.py
@@ -8,7 +8,7 @@
 import pytest
 
 from ttsim import InputData, MainTarget, TTTargets, main
-from ttsim.tt_dag_elements.column_objects_param_function import policy_function
+from ttsim.tt.column_objects_param_function import policy_function
 
 if TYPE_CHECKING:
     from types import ModuleType
diff --git a/tests/test_interface_dag.py b/tests/test_interface_dag.py
index 3967cb88e..933c6cdea 100644
--- a/tests/test_interface_dag.py
+++ b/tests/test_interface_dag.py
@@ -8,7 +8,13 @@
 import pytest
 
 from ttsim import InputData, OrigPolicyObjects, TTTargets
-from ttsim.interface_dag import (
+from ttsim.interface_dag_elements.fail_if import format_list_linewise
+from ttsim.interface_dag_elements.interface_node_objects import (
+    fail_function,
+    input_dependent_interface_function,
+    interface_function,
+)
+from ttsim.main import (
     _fail_if_input_structure_is_invalid,
     _fail_if_requested_nodes_cannot_be_found,
     _fail_if_root_nodes_of_interface_dag_are_missing,
@@ -18,15 +24,9 @@
     _resolve_dynamic_interface_objects_to_static_nodes,
     load_flat_interface_functions_and_inputs,
 )
-from ttsim.interface_dag_elements import MainTarget
-from ttsim.interface_dag_elements.fail_if import format_list_linewise
-from ttsim.interface_dag_elements.interface_node_objects import (
-    fail_function,
-    input_dependent_interface_function,
-    interface_function,
-)
+from ttsim.main_target import MainTarget
 from ttsim.plot_dag import dummy_callable
-from ttsim.tt_dag_elements.column_objects_param_function import policy_function
+from ttsim.tt.column_objects_param_function import policy_function
 
 
 @interface_function(leaf_name="interface_function_a")
diff --git a/tests/test_plot_dag.py b/tests/test_plot_dag.py
index 11991f721..07ba47317 100644
--- a/tests/test_plot_dag.py
+++ b/tests/test_plot_dag.py
@@ -4,13 +4,13 @@
 
 import pytest
 
-from ttsim.interface_dag import main
+from ttsim.main import main
 from ttsim.plot_dag import (
     _get_tt_dag_with_node_metadata,
     _QNameNodeSelector,
     plot_interface_dag,
 )
-from ttsim.tt_dag_elements import (
+from ttsim.tt import (
     ScalarParam,
     param_function,
     policy_function,
diff --git a/tests/tt_dag_elements/test_aggregation_functions.py b/tests/tt_dag_elements/test_aggregation_functions.py
index 870185dcb..0bb1bcf21 100644
--- a/tests/tt_dag_elements/test_aggregation_functions.py
+++ b/tests/tt_dag_elements/test_aggregation_functions.py
@@ -13,7 +13,7 @@
     my_datetime = lambda x: x  # noqa: E731
 
 
-from ttsim.tt_dag_elements.aggregation import (
+from ttsim.tt.aggregation import (
     grouped_all,
     grouped_any,
     grouped_count,
diff --git a/tests/tt_dag_elements/test_piecewise_polynomial.py b/tests/tt_dag_elements/test_piecewise_polynomial.py
index e2610c56e..ad1921ed7 100644
--- a/tests/tt_dag_elements/test_piecewise_polynomial.py
+++ b/tests/tt_dag_elements/test_piecewise_polynomial.py
@@ -13,7 +13,7 @@
     from types import ModuleType
 
 
-from ttsim.tt_dag_elements.piecewise_polynomial import (
+from ttsim.tt.piecewise_polynomial import (
     PiecewisePolynomialParamValue,
     get_piecewise_parameters,
     piecewise_polynomial,
diff --git a/tests/tt_dag_elements/test_rounding.py b/tests/tt_dag_elements/test_rounding.py
index 42feb586c..f27369741 100644
--- a/tests/tt_dag_elements/test_rounding.py
+++ b/tests/tt_dag_elements/test_rounding.py
@@ -8,7 +8,7 @@
 from pandas._testing import assert_series_equal
 
 from ttsim import main
-from ttsim.tt_dag_elements import (
+from ttsim.tt import (
     RoundingSpec,
     policy_function,
     policy_input,
diff --git a/tests/tt_dag_elements/test_shared.py b/tests/tt_dag_elements/test_shared.py
index 245750bbd..ce0a72f78 100644
--- a/tests/tt_dag_elements/test_shared.py
+++ b/tests/tt_dag_elements/test_shared.py
@@ -5,12 +5,12 @@
 import numpy
 import pytest
 
-from ttsim.tt_dag_elements import join
+from ttsim.tt import join
 
 if TYPE_CHECKING:
     from types import ModuleType
 
-    from ttsim.interface_dag_elements.typing import IntColumn
+    from ttsim.typing import IntColumn
 
 
 @pytest.mark.parametrize(
diff --git a/tests/tt_dag_elements/test_ttsim_objects.py b/tests/tt_dag_elements/test_ttsim_objects.py
index f1b2f2406..7bb3b6c09 100644
--- a/tests/tt_dag_elements/test_ttsim_objects.py
+++ b/tests/tt_dag_elements/test_ttsim_objects.py
@@ -4,7 +4,7 @@
 
 import pytest
 
-from ttsim.tt_dag_elements import (
+from ttsim.tt import (
     AggType,
     PolicyFunction,
     PolicyInput,
@@ -13,7 +13,7 @@
     policy_function,
     policy_input,
 )
-from ttsim.tt_dag_elements.column_objects_param_function import (
+from ttsim.tt.column_objects_param_function import (
     ParamFunction,
     param_function,
 )
diff --git a/tests/tt_dag_elements/test_vectorization.py b/tests/tt_dag_elements/test_vectorization.py
index aaca76c5a..78ffe6c45 100644
--- a/tests/tt_dag_elements/test_vectorization.py
+++ b/tests/tt_dag_elements/test_vectorization.py
@@ -18,16 +18,16 @@
 from ttsim.interface_dag_elements.policy_environment import (
     _active_column_objects_and_param_functions,
 )
-from ttsim.tt_dag_elements import (
+from ttsim.tt import (
     GroupCreationFunction,
     PolicyInput,
     policy_function,
 )
-from ttsim.tt_dag_elements.column_objects_param_function import (
+from ttsim.tt.column_objects_param_function import (
     AggByGroupFunction,
     AggByPIDFunction,
 )
-from ttsim.tt_dag_elements.vectorization import (
+from ttsim.tt.vectorization import (
     TranslateToVectorizableError,
     _is_lambda_function,
     _make_vectorizable,
@@ -38,7 +38,7 @@
 if TYPE_CHECKING:
     from types import ModuleType
 
-    from ttsim.interface_dag_elements.typing import IntColumn
+    from ttsim.typing import IntColumn
 
 # ======================================================================================
 # String comparison