diff --git a/router/functionHandler.go b/router/functionHandler.go
index 6464be63..af9f25bd 100644
--- a/router/functionHandler.go
+++ b/router/functionHandler.go
@@ -29,7 +29,7 @@ import (
 type functionHandler struct {
 	fmap           *functionServiceMap
 	poolManagerUrl string
-	fission.Function
+	Function       fission.Metadata
 }
 
 func (*functionHandler) getServiceForFunction() (*url.URL, error) {
diff --git a/router/functionHandler_test.go b/router/functionHandler_test.go
index 274b199a..2d7537a8 100644
--- a/router/functionHandler_test.go
+++ b/router/functionHandler_test.go
@@ -49,7 +49,7 @@ func TestFunctionProxying(t *testing.T) {
 	backendURL := createBackendService(testResponseString)
 	log.Printf("Created backend svc at %v", backendURL)
 
-	fn := &fission.Function{Name: "foo", Uid: "xxx"}
+	fn := &fission.Metadata{Name: "foo", Uid: "xxx"}
 	fmap := makeFunctionServiceMap()
 	fmap.assign(fn, backendURL)
 
diff --git a/router/functionServiceMap.go b/router/functionServiceMap.go
index 23394315..671c19bc 100644
--- a/router/functionServiceMap.go
+++ b/router/functionServiceMap.go
@@ -38,7 +38,7 @@ type functionServiceMapResponse struct {
 	error
 }
 type functionServiceMapRequest struct {
-	fission.Function
+	Function   fission.Metadata
 	serviceUrl url.URL
 	requestType
 	responseChannel chan<- functionServiceMapResponse
@@ -50,7 +50,7 @@ type functionServiceMapEntry struct {
 
 type functionServiceMap struct {
 	// map (funcname, uid) -> url
-	svc               map[fission.Function]functionServiceMapEntry
+	svc               map[fission.Metadata]functionServiceMapEntry
 	currentGeneration uint64
 	requestChannel    chan *functionServiceMapRequest
 }
@@ -58,7 +58,7 @@ type functionServiceMap struct {
 func makeFunctionServiceMap() *functionServiceMap {
 	fmap := &functionServiceMap{}
 	fmap.requestChannel = make(chan *functionServiceMapRequest)
-	fmap.svc = make(map[fission.Function]functionServiceMapEntry)
+	fmap.svc = make(map[fission.Metadata]functionServiceMapEntry)
 	go fmap.functionServiceMapWork()
 	return fmap
 }
@@ -89,7 +89,7 @@ func (fmap *functionServiceMap) functionServiceMapWork() {
 	}
 }
 
-func (fmap *functionServiceMap) lookup(f *fission.Function) (*url.URL, error) {
+func (fmap *functionServiceMap) lookup(f *fission.Metadata) (*url.URL, error) {
 	respChannel := make(chan functionServiceMapResponse)
 	fmap.requestChannel <- &functionServiceMapRequest{Function: *f, requestType: LOOKUP, responseChannel: respChannel}
 	resp := <-respChannel
@@ -100,7 +100,7 @@ func (fmap *functionServiceMap) lookup(f *fission.Function) (*url.URL, error) {
 	}
 }
 
-func (fmap *functionServiceMap) assign(f *fission.Function, serviceUrl *url.URL) {
+func (fmap *functionServiceMap) assign(f *fission.Metadata, serviceUrl *url.URL) {
 	fmap.requestChannel <- &functionServiceMapRequest{Function: *f, serviceUrl: *serviceUrl, requestType: ASSIGN}
 }
 
diff --git a/router/functionServiceMap_test.go b/router/functionServiceMap_test.go
index 94c8f9df..9a57cc56 100644
--- a/router/functionServiceMap_test.go
+++ b/router/functionServiceMap_test.go
@@ -25,7 +25,7 @@ import (
 
 func TestFunctionServiceMap(t *testing.T) {
 	m := makeFunctionServiceMap()
-	fn := &fission.Function{Name: "foo", Uid: "012"}
+	fn := &fission.Metadata{Name: "foo", Uid: "012"}
 	u, err := url.Parse("/foo012")
 	if err != nil {
 		t.Errorf("can't parse url")
diff --git a/router/router_test.go b/router/router_test.go
index 59aca9f0..119d035a 100644
--- a/router/router_test.go
+++ b/router/router_test.go
@@ -26,7 +26,7 @@ import (
 
 func TestRouter(t *testing.T) {
 	fmap := makeFunctionServiceMap()
-	fn := &fission.Function{Name: "foo", Uid: "xxx"}
+	fn := &fission.Metadata{Name: "foo", Uid: "xxx"}
 
 	testResponseString := "hi"
 	testServiceUrl := createBackendService(testResponseString)
@@ -35,7 +35,7 @@ func TestRouter(t *testing.T) {
 
 	triggers := makeHTTPTriggerSet(fmap, "", "")
 	triggerUrl := "/foo"
-	triggers.triggers = append(triggers.triggers, fission.HTTPTrigger{triggerUrl, *fn})
+	triggers.triggers = append(triggers.triggers, fission.HTTPTrigger{UrlPattern: triggerUrl, Function: *fn})
 
 	port := 4242
 	go server(port, triggers)
diff --git a/types.go b/types.go
index ad4e252e..01b08d2d 100644
--- a/types.go
+++ b/types.go
@@ -17,13 +17,41 @@ limitations under the License.
 package fission
 
 type (
-	Function struct {
+	// Metadata is used as the general identifier for all kinds of
+	// resources managed by the controller.  In general, when a
+	// resource is updated, the Name remains the same, but the UID
+	// changes.  In other words, the UID identifies a particular
+	// value of a resource.
+	Metadata struct {
 		Name string
 		Uid  string
 	}
 
+	// Function is a unit of executable code.  Though it's called
+	// a function, the code may have more than one function; it's
+	// usually some sort of module or package.
+	Function struct {
+		Metadata
+		Environment Metadata
+		Code        string
+	}
+
+	// Environment identifies the language and OS specific
+	// resources that a function depends on.  For now this
+	// includes only the function run container image.  Later,
+	// this will also include build containers, as well as support
+	// tools like debuggers, profilers, etc.
+	Environment struct {
+		Metadata
+		RunContainerImageUrl string
+	}
+
+	// HTTPTrigger maps URL patterns to functions.  Function.UID
+	// is optional; if absent, the latest version of the function
+	// will automatically be selected.
 	HTTPTrigger struct {
+		Metadata
 		UrlPattern string
-		Function
+		Function   Metadata
 	}
 )