AliasDataFrame: Add support for __getattr__ access to subframes and chained aliases

- Enable dot-access syntax (e.g. adf.track.pt, adf.track.collision.z)
- Automatically resolve and evaluate subframe aliases recursively
- Preserve subframe metadata in ROOT and Parquet exports
- Update unit tests to validate __getattr__ and nested access
- Update documentation (AliasDataFrame.md) with realistic subframe usage example

Author: miranov25

UTILS/dfextensions/AliasDataFrame.md

@@ -27,12 +27,22 @@ adf.materialize_alias("pt")
 Reference a subframe (e.g. per-cluster frame linked to a per-track frame):
 
 ```python
-adf_clusters.register_subframe("T", adf_tracks, index_columns=["track_index"])
-adf_clusters.add_alias("dX", "mX - T.mX")
-adf_clusters.materialize_alias("dX")
+adf_clusters.register_subframe("track", adf_tracks, index_columns="track_index")
+adf_tracks.register_subframe("collision", adf_collisions, index_columns="collision_index")
+
+adf_clusters.add_alias("dX", "mX - track.mX")
+adf_clusters.add_alias("vertexZ", "track.collision.z")
 ```
 
-Under the hood, this performs a join using `track_index` between clusters and tracks, rewrites `T.mX` to the joined column, and evaluates in that context.
+Under the hood, this performs joins using index columns such as `track_index` and `collision_index`, rewrites dotted expressions like `track.mX` and `track.collision.z` to joined columns, and evaluates in that context.
+
+For example, in ALICE data:
+
+- clusters reference tracks: `cluster → track`
+- tracks reference collisions: `track → collision`
+- V0s reference two tracks: `v0 → track1`, `v0 → track2`
+
+These relations can be declared using `register_subframe()` and used symbolically in aliases.
 
 ### ✅ Dependency Graph & Cycle Detection
 
@@ -50,6 +60,15 @@ adf.plot_alias_dependencies()
 adf.add_alias("scale", "1.5", dtype=np.float32, is_constant=True)
 ```
 
+### ✅ Attribute Access for Aliases and Subframes
+
+Access aliases and subframe members with convenient dot notation:
+
+```python
+adf.cutHighPt  # equivalent to adf["cutHighPt"]
+adf.track.pt   # evaluates pt from registered subframe "track"
+```
+
 ---
 
 ## 💾 Persistence
@@ -91,6 +110,7 @@ Tests included for:
 * Constant and hierarchical aliasing
 * Partial materialization
 * Subframe joins on index columns
+* Chained access via `adf.attr` and `adf.subframe.alias`
 * Persistence round-trips for `.parquet` and `.root`
 * Error detection: cycles, invalid expressions, undefined symbols
 
@@ -161,20 +181,20 @@ It brings the clarity of a computation graph to structured table analysis — a
 
 * [ ] Secure expression parser (no raw `eval`)
 * [ ] Aliased column caching / invalidation strategy
-* [ ] Inter-subframe join strategies (e.g., key-based, 1\:n)
+* [ ] Inter-subframe join strategies (e.g., key-based, 1: n)
 * [ ] Jupyter widget or CLI tool for alias graph exploration
 * [ ] Broadcasting-aware joins or 2D index support
 
 ---
 
 ## 🧑‍🔬 Designed for...
 
-* Physics workflows (e.g. ALICE clusters ↔ tracks ↔ collisions)
+* Physics workflows (e.g. ALICE Physics analysis V0 ↔ tracks ↔ collisions)
 * Symbolic calibration / correction workflows
 * Structured data exports with traceable metadata
 
 ---
 
-**Author:** \[You]
+**Author:** Marian Ivanov
 
 MIT License