diff --git a/WeakLensingValidation/catalog.py b/WeakLensingValidation/catalog.py
new file mode 100644
index 0000000..9d7bbe2
--- /dev/null
+++ b/WeakLensingValidation/catalog.py
@@ -0,0 +1,209 @@
+# Author: Axel Guinot (axel.guinot.astro@gmail.com)
+# Catalogue
+
+from config_parser import ConfigParser
+
+# This is used with the eval function
+import dask.array as da
+import vaex
+from vaex.convert import convert
+
+import numpy as np
+
+import os
+import copy
+
+
+class Catalog():
+    """Catalog
+
+    This class store a catalog as multiple DaskArrays.
+    This class is instenciate from a config file.
+    """
+
+    def __init__(
+        self,
+        path=None,
+        config=None,
+        params=None,
+    ):
+
+        if isinstance(config, ConfigParser):
+            self._config = config.config
+        else:
+            raise ValueError(
+                f"config must be an instance of {ConfigParser}. "
+                f"Got: {type(config)}"
+            )
+
+        self.read_catalog()
+
+    def __getitem__(self, key):
+
+        if not isinstance(key, str):
+            raise KeyError("Key must be a string")
+        if key not in self.column_names:
+            raise KeyError(f"{key}")
+        return self._columns[key]
+
+    def read_catalog(self):
+
+        raise NotImplementedError
+
+    def _read_catalog(self, cat_config):
+        """read catalog
+
+        This method handle the reading of a catalog. It can read multiple
+        catalogs and return a single Dataframe. If requested, it will keep
+        track of the origin catalog for every objects.
+
+        Parameters
+        ----------
+        cat_config : dict
+            Configuration dictionnary
+        """
+
+        path_config = cat_config['path']
+
+        # Here we handle the opeinig of multiple files like vaex.open_many()
+        # but we also keep track of the catalog of origin for each objects if
+        # requested.
+        all_df = []
+        for i, path in enumerate(path_config['path']):
+            # First we check the extension of the file. If not ".hdf5" we
+            # convert it. We cannot make memory mapped operations from ".fits"
+            # file. The converted file is put in the workspace directory.
+            ext = os.path.splitext(path)[1]
+            file_name = os.path.split(path)[1]
+            if ext != '.hdf5':
+                new_path = \
+                    self._config["workspace"]['path'] + '/' \
+                    + file_name + '.hdf5'
+                if ext != '.fits':
+                    raise ValueError(f"Unreconized file format. Got: {ext}")
+                if not os.path.exists(new_path):
+                    convert(
+                        path_input=path,
+                        fs_options_input={},
+                        fs_input=None,
+                        path_output=new_path,
+                        fs_options_output={},
+                        fs_output=None,
+                        progress=False,
+                    )
+            else:
+                new_path = \
+                    self._config["workspace"]['path'] + '/' + file_name
+                if not os.path.exists(new_path):
+                    os.symlink(path, new_path)
+
+            # Now we handle the history if requested
+            df_tmp = vaex.open(new_path)
+            if path_config['keep_cat_history']:
+                # Check if it has alreay been added
+                if 'var_cat_history' not in df_tmp.column_names:
+                    df_tmp['var_cat_history'] = \
+                        np.ones(len(df_tmp), dtype=int) \
+                        * path_config['var_cat_history'][i]
+            all_df.append(df_tmp)
+        self._df = vaex.concat(all_df)
+
+    def _get_column(self, col_name, all_col_names):
+        """get column
+
+        Build all the column of the catalog and convert them to DaskArray
+
+        Parameters
+        ----------
+        col_name : str, dict
+            Column name in the original catalog or dictionnary with a
+            description of how to build the column.
+        all_col_names : list
+            List of all the column names in the original catalog.
+
+        Returns
+        -------
+        dask.array
+            DaskArray of the column
+        """
+
+        if isinstance(col_name, str):
+            return self._df[col_name].to_dask_array()
+        elif isinstance(col_name, dict):
+            cat_tmp = {}
+            func = copy.copy(col_name['func'])
+            for var_name in col_name['var']:
+                cat_tmp[var_name] = self._df[var_name].to_dask_array()
+                func = func.replace(
+                    f"${var_name}$", f"cat_tmp['{var_name}']"
+                )
+            try:
+                res = eval(func)
+            except Exception as e:
+                raise ValueError(
+                        f"Error while evaluating function: \n{func}\n"
+                        f"Got exception: \n{e}"
+                    )
+            return res
+
+
+class GalaxyCatalog(Catalog):
+
+    def __init__(
+            self,
+            config=None
+    ):
+
+        super().__init__(config=config)
+
+    def read_catalog(self):
+        """read catalogue
+
+        This function is called during the initialization and build the galaxy
+        catalog.
+        """
+
+        cat_config = self._config['galaxy_catalog']
+
+        # First we read the catalog with vaex
+        self._read_catalog(cat_config)
+
+        # Now we set the column as dask arrays
+        self.column_names = list(cat_config['columns'].keys())
+        self._columns = {}
+        for column_name in self.column_names:
+            self._columns[column_name] = self._get_column(
+                cat_config['columns'][column_name],
+                self.column_names,
+            )
+
+
+class StarCatalog(Catalog):
+
+    def __init__(
+            self,
+            config=None
+    ):
+
+        super().__init__(config=config)
+
+    def read_catalog(self):
+        """read catalogue
+
+        This function is called during the initialization and build the star
+        catalog.
+        """
+
+        cat_config = self._config['star_catalog']
+
+        # First we read the catalog with vaex
+        self._read_catalog(cat_config)
+
+        # Now we set the column as dask arrays
+        self.column_names = list(cat_config['columns'].keys())
+        self._columns = {}
+        for column_name in self.column_names:
+            self._columns[column_name] = self._get_column(
+                cat_config['columns'][column_name],
+                self.column_names,
+            )