diff --git a/bam_masterdata/metadata/data_classes.py b/bam_masterdata/metadata/data_classes.py
new file mode 100644
index 0000000..b1b045d
--- /dev/null
+++ b/bam_masterdata/metadata/data_classes.py
@@ -0,0 +1,211 @@
+import json
+from collections.abc import Callable
+from dataclasses import dataclass
+from pathlib import Path
+from typing import Any
+
+from lxml import etree
+
+
+class Resource:
+    """
+    Base class for all resources.
+
+    A resource represents a data source (e.g. XML, JSON)
+    that can be queried using a selector language.
+    """
+
+    def query(self, selector: str, selector_type: str) -> Any:
+        raise NotImplementedError("Resource.query must be implemented in subclasses")
+
+
+# -------------------------
+# XML RESOURCE
+# -------------------------
+
+
+@dataclass
+class XMLResource(Resource):
+    """
+    XML file wrapper using lxml.
+
+    Supports XPath queries.
+    """
+
+    path: Path
+
+    def __post_init__(self):
+        try:
+            self.tree = etree.parse(str(self.path))
+        except OSError as e:
+            raise FileNotFoundError(
+                f"XML file not found or unreadable: {self.path}"
+            ) from e
+        except etree.XMLSyntaxError as e:
+            raise ValueError(f"Invalid XML syntax in file: {self.path}") from e
+
+    def query(self, selector: str, selector_type: str) -> Any:
+        """
+        Execute an XPath query on the XML document.
+        """
+        if selector_type != "xpath":
+            raise ValueError(f"Unsupported selector type for XML: {selector_type}")
+
+        try:
+            result = self.tree.xpath(selector)
+        except Exception as e:
+            raise ValueError(f"Invalid XPath expression: {selector}") from e
+
+        if not result:
+            return None
+
+        return result[0] if len(result) == 1 else result
+
+
+# -------------------------
+# JSON RESOURCE
+# -------------------------
+
+
+@dataclass
+class JSONResource(Resource):
+    """
+    JSON file wrapper.
+
+    Supports dot-notation queries like:
+    "sample.name"
+    """
+
+    path: Path
+
+    def __post_init__(self):
+        try:
+            with open(self.path, encoding="utf-8") as f:
+                self.data = json.load(f)
+        except FileNotFoundError as e:
+            raise FileNotFoundError(f"JSON file not found: {self.path}") from e
+        except json.JSONDecodeError as e:
+            raise ValueError(f"Invalid JSON in file: {self.path}") from e
+
+    def query(self, selector: str, selector_type: str) -> Any:
+        """
+        Resolve a dot-separated path inside JSON.
+        Example: "instrument.voltage"
+        """
+        if selector_type != "jsonpath":
+            raise ValueError(f"Unsupported selector type for JSON: {selector_type}")
+
+        try:
+            value = self.data
+            for key in selector.split("."):
+                value = value[key]
+            return value
+        except KeyError as e:
+            raise KeyError(f"Key '{key}' not found in JSON path '{selector}'") from e
+        except TypeError as e:
+            raise ValueError(f"Invalid structure while resolving '{selector}'") from e
+
+
+# -------------------------
+# MAPPING
+# -------------------------
+
+
+@dataclass
+class FieldMapping:
+    """
+    Defines how one field is extracted from a resource.
+
+    Attributes:
+        source: filename/key in resources dict
+        selector: query expression (XPath or dot notation)
+        selector_type: "xpath" or "jsonpath"
+        transform: optional conversion function (e.g. float, int)
+    """
+
+    source: str
+    selector: str
+    selector_type: str
+    transform: Callable[[Any], Any] | None = None
+
+
+@dataclass
+class ObjectMapping:
+    """
+    Defines how a target object is constructed from multiple fields.
+    """
+
+    target: type
+    fields: dict[str, FieldMapping]
+
+
+# -------------------------
+# BUILDER
+# -------------------------
+
+
+class ObjectBuilder:
+    """
+    Builds domain objects from resources based on an ObjectMapping.
+
+    Example:
+        builder = ObjectBuilder(mapping)
+        obj = builder.build(resources)
+    """
+
+    def __init__(self, mapping: ObjectMapping):
+        self.mapping = mapping
+
+    def build(self, resources: dict[str, Resource]):
+        """
+        Create an instance of the target class.
+
+        Args:
+            resources: dict of loaded resources (XML/JSON/etc.)
+
+        Raises:
+            KeyError: if a required resource is missing
+            ValueError: if query or transformation fails
+        """
+        values = {}
+
+        for field_name, field_mapping in self.mapping.fields.items():
+            # --- resource lookup ---
+            try:
+                resource = resources[field_mapping.source]
+            except KeyError as e:
+                raise KeyError(
+                    f"Resource '{field_mapping.source}' not found. "
+                    f"Available: {list(resources.keys())}"
+                ) from e
+
+            # --- query execution ---
+            try:
+                value = resource.query(
+                    field_mapping.selector,
+                    field_mapping.selector_type,
+                )
+            except Exception as e:
+                raise ValueError(
+                    f"Query failed for field '{field_name}' "
+                    f"using selector '{field_mapping.selector}'"
+                ) from e
+
+            # --- transformation ---
+            try:
+                if field_mapping.transform:
+                    value = field_mapping.transform(value)
+            except Exception as e:
+                raise ValueError(
+                    f"Transform failed for field '{field_name}' with value {value}"
+                ) from e
+
+            values[field_name] = value
+
+        try:
+            return self.mapping.target(**values)
+        except Exception as e:
+            raise TypeError(
+                f"Failed to construct {self.mapping.target.__name__} "
+                f"with values {values}"
+            ) from e