diff --git a/deployment/data-model-test.nix b/deployment/data-model-test.nix
index 0deeb563..5e4879d3 100644
--- a/deployment/data-model-test.nix
+++ b/deployment/data-model-test.nix
@@ -13,6 +13,7 @@ let
         ./data-model.nix
       ];
     }).config;
+  nixops4Deployment = inputs.nixops4.modules.nixops4Deployment.default;
 in
 {
   test-eval = {
diff --git a/deployment/data-model.nix b/deployment/data-model.nix
index de58f351..0d3868ee 100644
--- a/deployment/data-model.nix
+++ b/deployment/data-model.nix
@@ -102,35 +102,57 @@ in
                 )
               );
             };
-            resource-mapping = mkOption {
+            implementation = mkOption {
               description = "Mapping of resources required by applications to available resources; the result can be deployed";
-              type = environment.config.function.implementation;
+              type = environment.config.resource-mapping.function-type;
             };
-            # TODO: somewhere we still need to
-            # - apply = { implementation = resource-mapping; input = <resource requirements of configured applications>; }
-            # - apply.output (deployment)
-            function = mkOption {
+            resource-mapping = mkOption {
               description = "Function type for the mapping from resources to a (NixOps4) deployment";
               type = submodule functionType;
               readOnly = true;
               default = {
                 input-type = application-resources;
-                output-type = submodule nixops4Deployment;
+                output-type = nixops4Deployment;
               };
             };
+            deployment = mkOption {
+              description = "Generate a deployment from a configuration";
+              type = functionTo environment.config.resource-mapping.output-type;
+              readOnly = true;
+              default =
+                cfg:
+                # TODO: check cfg.enable.true
+                let
+                  required-resources = lib.mapAttrs (
+                    name: application-settings: config.applications.${name}.resources application-settings
+                  ) cfg.applications;
+                in
+                (environment.config.implementation required-resources).output;
+
+            };
           };
         })
       );
     };
-    configurations = mkOption {
-      description = "Application configurations set by operators";
-      type = attrsOf (submodule {
+    configuration = mkOption {
+      description = "Configuration type declaring options to be set by operators";
+      type = optionType;
+      readOnly = true;
+      default = submodule (configuration: {
         options = {
           enable = mkOption {
             description = "Whether to enable the configuration";
             type = types.bool;
+            default = false;
           };
-          applications = mapAttrs (name: application: submodule application.module) config.applications;
+          applications = lib.mapAttrs (
+            name: application:
+            mkOption {
+              description = application.description;
+              type = submodule application.module;
+              default = { };
+            }
+          ) config.applications;
         };
       });
     };
diff --git a/deployment/interface.nix b/deployment/interface.nix
deleted file mode 100644
index 225526d1..00000000
--- a/deployment/interface.nix
+++ /dev/null
@@ -1,49 +0,0 @@
-/**
-  Modular function type
-*/
-{ config, ... }:
-{
-  options = {
-    input-type = mkOption {
-      type = deferredModule;
-    };
-    output-type = mkOption {
-      type = deferredModule;
-    };
-    implementation = mkOption {
-      type = optionType;
-      readOnly = true;
-      default = implementationTo (
-        submodule (implementation: {
-          options = {
-            input = mkOption {
-              type = submodule config.input-type;
-            };
-            output = mkOption {
-              type = submodule config.output-type;
-            };
-          };
-        })
-      );
-    };
-    apply = mkOption {
-      type = optionType;
-      readOnly = true;
-      default = submodule (apply: {
-        options = {
-          implementation = mkOption {
-            type = config.implementation;
-          };
-          input = mkOption {
-            type = submodule config.input-type;
-          };
-          output = mkOption {
-            type = submodule config.output-type;
-            readOnly = true;
-            default = (apply.config.implementation apply.config.input).output;
-          };
-        };
-      });
-    };
-  };
-}