diff --git a/src/bedit_core/modelica/__init__.py b/src/bedit_core/modelica/__init__.py
new file mode 100644
index 0000000..e2c0ce1
--- /dev/null
+++ b/src/bedit_core/modelica/__init__.py
@@ -0,0 +1,6 @@
+from .compose import CompositionResult, compose_modelica_model
+
+__all__ = [
+    "CompositionResult",
+    "compose_modelica_model"
+]
\ No newline at end of file
diff --git a/src/bedit_core/modelica/compose.py b/src/bedit_core/modelica/compose.py
new file mode 100644
index 0000000..6d6707a
--- /dev/null
+++ b/src/bedit_core/modelica/compose.py
@@ -0,0 +1,260 @@
+from __future__ import annotations
+from dataclasses import dataclass
+import re
+from bedit_core.models import (
+    Component, 
+    BondPort, 
+    GraphImplementation, 
+    ValueType, 
+    SignalDirection, 
+    Port,
+    SignalPort,
+    PortID,
+    Parameter,
+    ParameterID,
+    EquationImplementation,
+    BondConnection,
+    SignalConnection,
+    ComponentID
+)
+
+_BEVALUE_PATTERN = re.compile(r"\$([A-Za-z0-9_-]+)\$")
+
+class CompositionError(ValueError):
+    pass
+
+@dataclass
+class CompositionResult:
+    modelica: str = ""
+    model_name: str = ""
+
+def compose_modelica_model(root: Component) -> CompositionResult:
+    composer = Composer(root)
+    return composer.compose()
+
+class Composer():
+    def __init__(self, root: Component)-> None:
+        self.model : str = ""
+        self.root : Component = root
+        self.indent: int = 0
+        self.lines: list[str] = []
+
+    def compose(self) -> CompositionResult:
+        self.indent = 0
+        self.lines = []
+
+        self.emit_model(self.root)
+
+        # Expand macros
+        macros = self.derive_macros(self.root, {})
+        for i in range(len(self.lines)):
+            self.lines[i] = self.expand_bevalues(self.lines[i], macros)
+
+        self.model = '\n'.join(self.lines)
+        return CompositionResult(self.model, self.model_name_for(self.root))
+
+    def emit_model(self, component: Component) -> None:
+        indentation = '\t'*self.indent
+        body_indentation = '\t'*(self.indent+1)
+        model_name = self.model_name_for(component)
+        macros: dict[str, str] = {}
+
+        self.lines.append(f"{indentation}model {model_name}")
+
+        # Add BondPort definition
+        if self.indent == 0:
+            self.lines.extend([
+                f"{body_indentation}connector BondPort",
+                f"{body_indentation}\tReal e;",
+                f"{body_indentation}\tflow Real f;",
+                f"{body_indentation}end BondPort;",
+            ])
+
+        # Emit subcomponents
+        if isinstance(component.implementation, GraphImplementation):
+            for c_id, c in component.implementation.graph.components.items():
+                self.indent += 1
+                self.emit_model(c)
+                self.indent -= 1
+
+        # Child models have already expanded their own name-based macros.
+        lines_start = len(self.lines)
+
+        # Interface
+        for port_id, port in component.interface.ports.items():
+            self.lines.append(f"{body_indentation}{self.port_declaration(port)};")
+            if port.multiplicity:
+                macros[f"{port.name}_N"] = f"${port_id}_N$"
+                macros[f"{port.name}_S"] = f"${port_id}_S$"
+
+        # Paramters
+        for param_id, param in component.parameters.items():
+            self.lines.append(f"{body_indentation}{self.param_declaration(param)};")
+
+        # declaration block if equation mode
+        if isinstance(component.implementation, EquationImplementation):
+            for line in component.implementation.declarations:
+                self.lines.append(f"{body_indentation}{line}")
+
+        # Component instantiations in graph mode
+        if isinstance(component.implementation, GraphImplementation):
+            for c_id, c in component.implementation.graph.components.items():
+                self.lines.append(f"{body_indentation}{self.model_name_for(c)} {c.name};")
+
+        # Initial equations if equation mode
+        if isinstance(component.implementation, EquationImplementation):
+            if len(component.implementation.initial_equations):
+                self.lines.append(f"{indentation}initial equation")
+                for line in component.implementation.initial_equations:
+                    self.lines.append(f"{body_indentation}{line}")
+
+        self.lines.append(f"{indentation}equation")
+
+        # equations block if equation mode
+        if isinstance(component.implementation, EquationImplementation):
+            for line in component.implementation.equations:
+                self.lines.append(f"{body_indentation}{line}")
+
+        # Connections if graph mode
+        elif isinstance(component.implementation, GraphImplementation):
+            port_indices: dict[PortID, int] = {}
+            for c_id, c in component.implementation.graph.connections.items():
+                source = component.implementation.graph.components[self.get_component_from_port(component, c.source)]
+                target = component.implementation.graph.components[self.get_component_from_port(component, c.target)]
+                source_port_name = self.port_reference(source.interface.ports[c.source], c.source, port_indices)
+                target_port_name = self.port_reference(target.interface.ports[c.target], c.target, port_indices)
+                if isinstance(c, BondConnection):
+                    self.lines.append(f"{body_indentation}connect({source.name}.{source_port_name}, {target.name}.{target_port_name});")
+                elif isinstance(c, SignalConnection):
+                    self.lines.append(f"{body_indentation}{target.name}.{target_port_name} = {source.name}.{source_port_name};")
+                else:
+                    raise CompositionError(f"Unknown connection type {type(c).__name__}")
+
+        else:
+            raise CompositionError(f"Unknown implementation type {type(component).__name__}")
+
+        # Fill in macros
+        for i in range(lines_start, len(self.lines)):
+            try:
+                self.lines[i] = self.expand_bevalues(self.lines[i], macros)
+            except CompositionError:
+                # Accept unresolved macros
+                pass
+
+        self.lines.append(f"{indentation}end {model_name};")
+
+    @staticmethod
+    def model_name_for(component: Component) -> str:
+        # TODO make sure model name is safe
+        return f"m_{component.name}"
+
+    @staticmethod
+    def modelica_type_from_ValueType(type: ValueType) -> str:
+        if type == ValueType.REAL:
+            return "Real"
+        elif type == ValueType.INT:
+            return "Integer"
+        elif type == ValueType.BOOL:
+            return "Boolean"
+        raise CompositionError(f"Unknown value type {type}")
+
+    @classmethod
+    def port_declaration(cls, port: Port) -> str:
+        direction = "output" if port.direction == SignalDirection.OUTPUT else "input"
+        name = port.name
+        dimensions = cls.port_dimensions(port)
+        if isinstance(port, BondPort):
+            return f"BondPort {name}{dimensions}"
+        elif isinstance(port, SignalPort):
+            port_type = cls.modelica_type_from_ValueType(port.value_type)
+            #TODO units
+            return f"{direction} {port_type} {name}{dimensions}"
+        raise CompositionError(f"Unknown port type {type(port).__name__}")
+
+    @classmethod
+    def fixed_dimensions(cls, p: Port | Parameter) -> str:
+        dimensions = p.matrix_size
+        rows = max(1, p.matrix_size[0])
+        columns = max(1, p.matrix_size[1])
+        if rows == columns == 1:
+            return ""
+        if columns == 1:
+            return f"[{rows}]"
+        return f"[{rows},{columns}]"
+
+    @classmethod
+    def port_dimensions(cls, port: Port) -> str:
+        fixed = cls.fixed_dimensions(port)
+        if not port.multiplicity:
+            return fixed
+        entries = [f"${port.name}_N$"]
+        if fixed:
+            entries.extend(fixed[1:-1].split(","))
+        return f"[{','.join(entries)}]"
+
+    @staticmethod
+    def expand_bevalues(text, values: dict[str, str]) -> str:
+        """Replace BEdit ``$name$`` macros and reject unresolved composer values."""
+        def replace(match: re.Match[str]) -> str:
+            name = match.group(1)
+            if name not in values:
+                raise CompositionError(f"Unknown BEdit value ${name}$")
+            return values[name]
+        return _BEVALUE_PATTERN.sub(replace, text)        
+
+    @classmethod
+    def param_declaration(cls, param: Parameter) -> str:
+        dimensions = cls.fixed_dimensions(param)
+        type = cls.modelica_type_from_ValueType(param.value_type)
+        # TODO units
+        return f"parameter {type} {param.name}{dimensions} = {param.value}"
+
+    def get_component_from_port(self, component: Component, port_id: PortID) -> ComponentID:
+        if isinstance(component.implementation, GraphImplementation):
+            for c_id, c in component.implementation.graph.components.items():
+                for p_id, p in c.interface.ports.items():
+                    if p_id == port_id:
+                        return c_id
+
+        raise CompositionError(f"Could not find component of port {port_id}")
+
+    @staticmethod
+    def port_reference(port: Port, port_id: PortID, indices: dict[PortID, int],) -> str:
+        """Return a port name with its one-based multiplicity index."""
+        if not port.multiplicity:
+            return port.name
+        index = indices.get(port_id, 0) + 1
+        indices[port_id] = index
+        return f"{port.name}[{index}]"
+
+    def derive_macros(self, component: Component, macros: dict[str, str]) -> dict[str, str]:
+        for port_id, port in component.interface.ports.items():
+            if port.multiplicity:
+                macros.setdefault(f"{port_id}_N", "0")
+                macros.setdefault(f"{port_id}_S", "{}")
+
+        if isinstance(component.implementation, GraphImplementation):
+            for c_id, c in component.implementation.graph.connections.items():
+                source = component.implementation.graph.components[self.get_component_from_port(component, c.source)]
+                target = component.implementation.graph.components[self.get_component_from_port(component, c.target)]
+                if source.interface.ports[c.source].multiplicity:
+                    self.record_multiplicity(macros, c.source, -1)
+                if target.interface.ports[c.target].multiplicity:
+                    self.record_multiplicity(macros, c.target, 1)
+
+            for c_id, c in component.implementation.graph.components.items():
+                macros = self.derive_macros(c, macros)
+
+        return macros
+
+    @staticmethod
+    def record_multiplicity(macros: dict[str, str], port_id: PortID, sign: int) -> None:
+        """Record a connection count and orientation for a multiplicity port."""
+        count_key = f"{port_id}_N"
+        signs_key = f"{port_id}_S"
+        macros[count_key] = str(int(macros.get(count_key, "0")) + 1)
+        signs = macros.get(signs_key, "{}")
+        entries = [] if signs == "{}" else signs[1:-1].split(", ")
+        entries.append(str(float(sign)))
+        macros[signs_key] = "{" + ", ".join(entries) + "}"
+    
diff --git a/src/bedit_core/models.py b/src/bedit_core/models.py
index 0d197e1..66b8b25 100644
--- a/src/bedit_core/models.py
+++ b/src/bedit_core/models.py
@@ -49,6 +49,11 @@ class PortCausality(Enum):
     SINGLE_EFFORT_IN = "single_effort_in"
     SINGLE_FLOW_IN = "single_flow_in"
 
+class ValueType(Enum):
+    REAL = "real"
+    BOOL = "bool"
+    INT = "int"
+
 @dataclass 
 class Document:
     format_version: int
@@ -78,7 +83,7 @@ class Port:
 
 @dataclass
 class SignalPort(Port):
-    value_type: str = "Real"
+    value_type: ValueType = ValueType.REAL
     quantity: str | None = None
     unit: str | None = None
 
@@ -91,7 +96,8 @@ class BondPort(Port):
 class Parameter:
     name: str
     value: Any = 1.0
-    value_type: str = "Real"
+    value_type: ValueType = ValueType.REAL
+    matrix_size: Annotated[list[int], 2] = field(default_factory=lambda: [1, 1])
     quantity: str | None = None
     unit: str | None = None
     description: str | None = None
diff --git a/src/bedit_core/serialization/schema.py b/src/bedit_core/serialization/schema.py
index a3edca7..3191e36 100644
--- a/src/bedit_core/serialization/schema.py
+++ b/src/bedit_core/serialization/schema.py
@@ -28,6 +28,7 @@ from bedit_core.models import (
     SignalConnection,
     SignalDirection,
     SignalPort,
+    ValueType
 )
 
 class SerializationError(ValueError):
@@ -118,7 +119,7 @@ def _port_to_data(port: Port) -> dict[str, Any]:
         return {
             "port_type": "signal",
             **common,
-            "value_type": port.value_type,
+            "value_type": _data_to_valuetype(port.value_type),
             "quantity": port.quantity,
             "unit": port.unit,
         }
@@ -131,7 +132,6 @@ def _port_to_data(port: Port) -> dict[str, Any]:
         }
     raise TypeError(f"unsupported port class: {type(port).__name__}")
 
-
 def _port_from_data(value: Any, where: str) -> Port:
     """Construct the port subclass selected by ``port_type``."""
     obj = _mapping(value, where)
@@ -146,7 +146,7 @@ def _port_from_data(value: Any, where: str) -> Port:
     if port_type == "signal":
         return SignalPort(
             **common,
-            value_type=_string(obj.get("value_type", "Real"), f"{where}.value_type"),
+            value_type=_valuetype_to_data(_string(obj.get("value_type", "Real"), f"{where}.value_type")),
             quantity=_optional_string(obj.get("quantity"), f"{where}.quantity"),
             unit=_optional_string(obj.get("unit"), f"{where}.unit"),
         )
@@ -162,13 +162,32 @@ def _port_from_data(value: Any, where: str) -> Port:
         )
     raise SerializationError(f"{where}.port_type: unsupported value {port_type!r}")
 
+def _data_to_valuetype(type: ValueType) -> str:
+    if type == ValueType.REAL:
+        return "real"
+    elif type == ValueType.INT:
+        return "int"
+    elif type == ValueType.BOOL:
+        return "bool"
+    raise SerializationError(f"Unknown value type {type}")
+
+def _valuetype_to_data(type: str) -> ValueType:
+    type = type.lower()
+    if type == "real":
+        return ValueType.REAL
+    elif type == "int":
+        return ValueType.INT
+    elif type == "bool":
+        return ValueType.BOOL
+    raise SerializationError(f"Unknown value type {type}")
 
 def _parameter_to_data(parameter: Parameter) -> dict[str, Any]:
     """Convert a parameter to raw values."""
     return {
         "name": parameter.name,
         "value": _plain_value(parameter.value),
-        "value_type": parameter.value_type,
+        "value_type": _data_to_valuetype(parameter.value_type),
+        "matrix_size": list(parameter.matrix_size),
         "quantity": parameter.quantity,
         "unit": parameter.unit,
         "description": parameter.description,
@@ -181,7 +200,8 @@ def _parameter_from_data(value: Any, where: str) -> Parameter:
     return Parameter(
         name=_string(_required(obj, "name", where), f"{where}.name"),
         value=obj.get("value", 1.0),
-        value_type=_string(obj.get("value_type", "Real"), f"{where}.value_type"),
+        value_type=_valuetype_to_data(_string(obj.get("value_type", "Real"), f"{where}.value_type")),
+        matrix_size=_matrix_size(obj.get("matrix_size", [1, 1]), f"{where}.matrix_size"),
         quantity=_optional_string(obj.get("quantity"), f"{where}.quantity"),
         unit=_optional_string(obj.get("unit"), f"{where}.unit"),
         description=_optional_string(obj.get("description"), f"{where}.description"),
diff --git a/tests/manual_test.py b/tests/manual_test.py
index df982fa..d72b855 100644
--- a/tests/manual_test.py
+++ b/tests/manual_test.py
@@ -1,11 +1,14 @@
 import sys
 from bedit_core.serialization import load, save
 from bedit_core.bondgraph import causality_inference
+from bedit_core.modelica import compose_modelica_model
 
 def main(path: str):
     doc = load(path)
     for id, root in doc.root.items():
         doc.root[id] = causality_inference(doc.root[id])
+        composition = compose_modelica_model(doc.root[id])
+        print(composition.modelica)
     save(doc, path)
 
 if __name__ == "__main__":
diff --git a/untitled.bedit.json b/untitled.bedit.json
index e8d9957..87baf04 100644
--- a/untitled.bedit.json
+++ b/untitled.bedit.json
@@ -5,7 +5,7 @@
   "name": "Current Document",
   "root": {
     "50e6ef97-f686-4400-bc01-e5a352e8cc22": {
-      "name": "New Graph Block 1",
+      "name": "test",
       "interface": {
         "ports": {}
       },
@@ -51,7 +51,11 @@
                 "parameter-d056bc27": {
                   "name": "c",
                   "value": "1",
-                  "value_type": "Real",
+                  "value_type": "real",
+                  "matrix_size": [
+                    1,
+                    1
+                  ],
                   "quantity": null,
                   "unit": null,
                   "description": null
@@ -128,7 +132,11 @@
                 "parameter-d056bc27": {
                   "name": "r",
                   "value": "1",
-                  "value_type": "Real",
+                  "value_type": "real",
+                  "matrix_size": [
+                    1,
+                    1
+                  ],
                   "quantity": null,
                   "unit": null,
                   "description": null
@@ -166,7 +174,11 @@
                 "parameter-d056bc27": {
                   "name": "e",
                   "value": "1",
-                  "value_type": "Real",
+                  "value_type": "real",
+                  "matrix_size": [
+                    1,
+                    1
+                  ],
                   "quantity": null,
                   "unit": null,
                   "description": null
@@ -242,7 +254,11 @@
                 "parameter-d056bc27": {
                   "name": "r",
                   "value": "10",
-                  "value_type": "Real",
+                  "value_type": "real",
+                  "matrix_size": [
+                    1,
+                    1
+                  ],
                   "quantity": null,
                   "unit": null,
                   "description": null
@@ -294,7 +310,11 @@
                 "parameter-d056bc27": {
                   "name": "i",
                   "value": "1",
-                  "value_type": "Real",
+                  "value_type": "real",
+                  "matrix_size": [
+                    1,
+                    1
+                  ],
                   "quantity": null,
                   "unit": null,
                   "description": null