diff --git a/pyproject.toml b/pyproject.toml
index e355c42..ad97f8c 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -17,6 +17,8 @@ dependencies = [
     "xarray",
     "scipy",
     "pandas",
+    "dask",
+    "netCDF4",
 ]
 
 [dependency-groups]
diff --git a/src/floatmatcher/products.py b/src/floatmatcher/products.py
new file mode 100644
index 0000000..4e61caf
--- /dev/null
+++ b/src/floatmatcher/products.py
@@ -0,0 +1,112 @@
+import xarray as xr
+from abc import ABC, abstractmethod
+from pathlib import Path
+from collections.abc import Sequence
+from typing import Self
+from dask.utils import SerializableLock
+
+
+from .pointset import PointSet
+from .resolver import FileResolver, ExplicitFiles, PathTemplate
+
+
+_NETCDF_LOCK = SerializableLock()
+
+# ─────────────────────────────────────────────────────────────
+
+# ─────────────────────────────────────────────────────────────
+
+def to_standard(ds: xr.Dataset, mapping: dict[str, str]) -> xr.Dataset:
+    """
+    Rename keys found in mapping. If key not found, skip and let it as it is.
+    set variables lon/lat/time as coords if not already
+    """
+  
+    renamable = set(ds.variables) | set(ds.dims)
+    valid={}
+    for src, dst in mapping.items() :
+        if src in renamable:
+            valid[src] = dst 
+                     
+    ds = ds.rename(valid)
+
+    # transform data var into coordinate if not already
+    to_promote = []
+    for name in ("lon", "lat", "time"):
+        if name in ds.data_vars:
+            to_promote.append(name)
+
+    ds = ds.set_coords(to_promote)
+    return ds
+
+
+
+class Product(ABC):
+    COORD_MAP: dict[str, str] = {}
+
+    def __init__(self, resolver: FileResolver | None = None) -> None:
+        self.resolver = resolver
+    
+    @classmethod
+    def from_local(cls, 
+                   path: str | Path | Sequence[str] | None = None,
+                   pattern: str | None = None) -> Self:
+        resolver: FileResolver
+        if pattern and not path:
+            raise ValueError("pattern given without a root path")
+        if not path:
+            raise ValueError("no path or pattern provided for opening data")
+
+        if pattern:
+            # a pattern is substituted under ONE root, not a list of paths
+            if not isinstance(path, (str, Path)):
+                raise ValueError("a pattern needs a single root path, not a list")
+            resolver = PathTemplate(path, pattern)
+        else:
+            resolver = ExplicitFiles(path)
+
+        return cls(resolver)
+
+    def files_for(self, points: PointSet | None = None) -> list[str]:
+        if self.resolver is None:
+            raise ValueError(
+                "this product carries no source; build it with "
+                f"{type(self).__name__}.from_local(...) before resolving files"
+            )
+        return self.resolver.files_for(points)
+
+    def open_paths(self, paths: Sequence[str]) -> xr.Dataset:
+        """ open several files as a xr mf_dataset with options
+        // lock option fix made by AI to avoid segfault : open_mfdataset 
+        returns dask arrays read by multiple threads, but netCDF4/HDF5 
+        isn't thread-safe here: concurrent access to xarray's file cache 
+        corrupted memory and killed the process. A single shared lock serialises
+        those reads //
+        """
+        if not paths:
+            raise ValueError("empty file list")
+        return xr.open_mfdataset(
+            paths,
+            combine="by_coords",
+            lock=_NETCDF_LOCK,
+            engine="netcdf4",
+            compat="override",
+            coords="minimal",
+        )
+    
+    @abstractmethod
+    def normalize(self, ds_raw: xr.Dataset) -> xr.Dataset:
+        ...
+
+
+class ERA5Product(Product):
+    COORD_MAP = {"longitude": "lon", "latitude": "lat", "valid_time": "time"}
+    def normalize(self, raw: xr.Dataset) -> xr.Dataset:
+        ds = to_standard(raw, self.COORD_MAP)
+        return ds
+    
+class LUTProduct(Product):
+    COORD_MAP = {"lon": "lon", "lat": "lat"}
+    def normalize(self, raw: xr.Dataset) -> xr.Dataset:
+        ds = to_standard(raw, self.COORD_MAP)
+        return ds
\ No newline at end of file
diff --git a/tests/test_products.py b/tests/test_products.py
new file mode 100644
index 0000000..81c836d
--- /dev/null
+++ b/tests/test_products.py
@@ -0,0 +1,114 @@
+# tests/test_products.py
+
+import numpy as np
+import numpy.testing as npt
+import xarray as xr
+import pytest
+
+from floatmatcher.resolver import PathTemplate, ExplicitFiles
+from floatmatcher.products import (
+    to_standard,
+    ERA5Product,
+    LUTProduct,
+)
+
+
+def _era5_raw():
+    """Raw ERA5-like dataset with source names longitude/latitude/time."""
+    return xr.Dataset(
+        {"t2m": (("valid_time", "latitude", "longitude"), np.zeros((2, 3, 3)))},
+        coords={
+            "valid_time": np.array(["2015-01-01", "2015-01-02"], dtype="datetime64[ns]"),
+            "latitude": [0.0, 1.0, 2.0],
+            "longitude": [10.0, 11.0, 12.0],
+        },
+    )
+
+
+# ───────────── to_standard ─────────────
+
+def test_rename_maps_present_keys():
+    out = to_standard(_era5_raw(), {"longitude": "lon", "latitude": "lat", "valid_time": "time"})
+    assert "lon" in out.coords and "lat" in out.coords and "time" in out.coords
+
+
+def test_rename_ignores_absent_keys():
+    out = to_standard(_era5_raw(), {"longitude": "lon", "foo": "bar"})
+    assert "lon" in out.coords
+    assert "bar" not in out.variables  # 'foo' does not exist -> skipped, not an error
+
+
+def test_rename_mapping_already_well_named():
+    ds = xr.Dataset({"chl": (("lat", "lon"), np.zeros((2, 2)))},
+                    coords={"lat": [0.0, 1.0], "lon": [10.0, 11.0]})
+    out = to_standard(ds, {"lon": "lon", "lat": "lat"})
+    assert "lon" in out.coords and "lat" in out.coords
+
+
+def test_rename_bare_dimension():
+    # a dimension without a coordinate can still be renamed
+    ds = xr.Dataset({"v": (("obs",), [1.0, 2.0, 3.0])})
+    out = to_standard(ds, {"obs": "points"})
+    assert "points" in out.dims and "obs" not in out.dims
+
+
+def test_data_variable_is_promoted_to_coord():
+    """lon/lat carried as data variables (anonymous dims) become coordinates:
+    GridSet reads them from ds.coords, never from ds.data_vars."""
+    ds = xr.Dataset(
+        {
+            "sst": (("y", "x"), np.zeros((2, 2))),
+            "latitude": (("y",), np.array([0.0, 1.0])),
+            "longitude": (("x",), np.array([10.0, 11.0])),
+        },
+    )
+    assert "latitude" in ds.data_vars                    # not a coord at this point
+
+    out = to_standard(ds, {"longitude": "lon", "latitude": "lat"})
+
+    assert "lon" in out.coords and "lat" in out.coords
+    assert "lon" not in out.data_vars and "lat" not in out.data_vars
+    npt.assert_allclose(out["lon"].values, [10.0, 11.0])
+
+
+def test_rename_does_not_affect_input():
+    ds = _era5_raw()
+    _ = to_standard(ds, {"longitude": "lon"})
+    assert "longitude" in ds.coords     # original left untouched
+
+
+
+# ───────────── Products ─────────────
+
+def test_era5_normalize():
+    out = ERA5Product().normalize(_era5_raw())
+    assert "lon" in out.coords and "lat" in out.coords and "time" in out.coords
+
+
+def test_lut_normalize():
+    ds = xr.Dataset({"chl": (("lat", "lon"), np.zeros((2, 2)))},
+                    coords={"lat": [0.0, 1.0], "lon": [-10.0, -9.0]})
+    out = LUTProduct().normalize(ds)
+    assert "lon" in out.coords and "lat" in out.coords
+
+
+def test_from_local_with_pattern_builds_a_pathtemplate():
+    product = ERA5Product.from_local(path="/data", pattern="{year}/x.nc")
+    assert isinstance(product.resolver, PathTemplate)
+
+
+def test_from_local_without_pattern_builds_explicitfiles():
+    product = ERA5Product.from_local(path="/data/2018")
+    assert isinstance(product.resolver, ExplicitFiles)
+
+
+def test_from_local_returns_the_good_product():
+    assert isinstance(ERA5Product.from_local(path="/data"), ERA5Product)
+    assert isinstance(LUTProduct.from_local(path="/data"), LUTProduct)
+
+
+def test_from_local_without_path_raise_error():
+    with pytest.raises(ValueError):
+        ERA5Product.from_local(pattern="{year}/x.nc")     # pattern sans path
+    with pytest.raises(ValueError):
+        ERA5Product.from_local() 
\ No newline at end of file