diff --git a/schema/xos-core.yang b/schema/xos-core.yang
index b7d2462..1c8de53 100644
--- a/schema/xos-core.yang
+++ b/schema/xos-core.yang
@@ -28,6 +28,7 @@
   
   import ietf-yang-types { prefix yang; }
   import ietf-inet-types { prefix inet; }
+  import xos-types { prefix xos; }
 
   feature synchronizer {
     description
@@ -263,6 +264,89 @@
     // TODO: should be able to deal with TenantWithContainer here
     
   }
+
+  grouping slice {
+    description 
+      "A slice is a logically centralized container for network and compute resources"
+
+    uses base-common;
+
+    leaf enabled {
+       type boolean;
+       default true;
+    }
+
+    leaf omf-friendly {
+       type boolean;
+       default false;
+       status deprecated;
+    }
+
+    leaf slice-url {
+       description "A URL describing the purpose of this slice";
+       type xos.refs.url-field; 
+       // blank true;
+    }
+
+    leaf max-instances {
+       description "The maximum number of VMs that this slice is allowed to allocate";
+       type uint32;
+    } 
+
+    leaf service {
+       description "The service that runs in this slice";
+       type xos.refs.service;
+    }
+
+    leaf network {
+       description "The network that the slice uses to connect to other slices and to the Internet.";
+       type string;
+    }
+
+    leaf exposed-ports {
+       description "The ports to be exposed for other slices to connect to";
+       type string;
+    }
+
+    leaf service-class {
+       type xos.refs.service-class;
+       status deprecated;
+    }
+   
+    leaf creator {
+       type xos.refs.user;
+    }
+
+    leaf default-flavor {
+       type xos.refs.flavor;
+    }
+
+    leaf default-image {
+       type xos.refs.image;
+    }
+
+    leaf default-node {
+       type xos.refs.node;
+    } 
+
+    leaf mount-data-sets {
+       type string;
+       default "GenBank";
+       length 0..256;
+    } 
+
+    leaf default_isolation {
+       type string;
+       default "vm";
+       length 0..30;
+    } 
+
+    leaf-list tags {
+        type leafref {
+            path "/tag[id = current()/../id]/id";
+        }
+    }
+  }
   
   /*** main configuration tree for XOS ***/
 
diff --git a/schema/xos-types.yang b/schema/xos-types.yang
new file mode 100644
index 0000000..0b786a4
--- /dev/null
+++ b/schema/xos-types.yang
@@ -0,0 +1,297 @@
+module xos-types {
+  namespace "urn:onlab:xos:types";
+  prefix xos-types;
+  yang-version 1.1;
+
+  organization
+   "Open Networking Lab (CORD) / Corenova Technologies";
+
+  contact
+    "Larry Peterson <llp@onlab.us>
+     Peter K. Lee <peter@corenova.com>";
+  
+  import ietf-yang-types { prefix yang; }
+  
+  revision 2016-09-12 {
+    description "Initial revision.";
+  }
+
+  grouping unique-identifier {
+    description "defines valid formats for external reference id";
+    type union {
+      type uint32 { range 1..max; }
+      type yang:uuid;
+      type inet:uri;
+    }
+  }
+
+  container refs {
+    grouping image {
+      uses unique-identifier;
+    }
+
+    grouping controller-network {
+      uses unique-identifier;
+    }
+
+    grouping site {
+      uses unique-identifier;
+    }
+
+    grouping tenant-root-role {
+      uses unique-identifier;
+    }
+
+    grouping slice-role {
+      uses unique-identifier;
+    }
+
+    grouping site-deployment {
+      uses unique-identifier;
+    }
+
+    grouping tenant-privilege {
+      uses unique-identifier;
+    }
+
+    grouping tag {
+      uses unique-identifier;
+    }
+
+    grouping user-credential {
+      uses unique-identifier;
+    }
+
+    grouping invoice {
+      uses unique-identifier;
+    }
+
+    grouping slice-privilege {
+      uses unique-identifier;
+    }
+
+    grouping flavor {
+      uses unique-identifier;
+    }
+
+    grouping port {
+      uses unique-identifier;
+    }
+
+    grouping service-role {
+      uses unique-identifier;
+    }
+
+    grouping controller-site {
+      uses unique-identifier;
+    }
+
+    grouping controller-slice {
+      uses unique-identifier;
+    }
+
+    grouping tenant-role {
+      uses unique-identifier;
+    }
+
+    grouping slice {
+      uses unique-identifier;
+    }
+
+    grouping network {
+      uses unique-identifier;
+    }
+
+    grouping controller-role {
+      uses unique-identifier;
+    }
+
+    grouping diag {
+      uses unique-identifier;
+    }
+
+    grouping service-class {
+      uses unique-identifier;
+    }
+
+    grouping tenant-attribute {
+      uses unique-identifier;
+    }
+
+    grouping site-role {
+      uses unique-identifier;
+    }
+
+    grouping subscriber {
+      uses unique-identifier;
+    }
+
+    grouping instance {
+      uses unique-identifier;
+    }
+
+    grouping charge {
+      uses unique-identifier;
+    }
+
+    grouping program {
+      uses unique-identifier;
+    }
+
+    grouping role {
+      uses unique-identifier;
+    }
+
+    grouping usable-object {
+      uses unique-identifier;
+    }
+
+    grouping node-label {
+      uses unique-identifier;
+    }
+
+    grouping slice-credential {
+      uses unique-identifier;
+    }
+
+    grouping node {
+      uses unique-identifier;
+    }
+
+    grouping address-pool {
+      uses unique-identifier;
+    }
+
+    grouping dashboard-view {
+      uses unique-identifier;
+    }
+
+    grouping network-parameter {
+      uses unique-identifier;
+    }
+
+    grouping image-deployments {
+      uses unique-identifier;
+    }
+
+    grouping controller-user {
+      uses unique-identifier;
+    }
+
+    grouping reserved-resource {
+      uses unique-identifier;
+    }
+
+    grouping network-template {
+      uses unique-identifier;
+    }
+
+    grouping controller-dashboard-view {
+      uses unique-identifier;
+    }
+
+    grouping user-dashboard-view {
+      uses unique-identifier;
+    }
+
+    grouping controller {
+      uses unique-identifier;
+    }
+
+    grouping user {
+      uses unique-identifier;
+    }
+
+    grouping deployment {
+      uses unique-identifier;
+    }
+
+    grouping reservation {
+      uses unique-identifier;
+    }
+
+    grouping site-privilege {
+      uses unique-identifier;
+    }
+
+    grouping payment {
+      uses unique-identifier;
+    }
+
+    grouping tenant {
+      uses unique-identifier;
+    }
+
+    grouping network-slice {
+      uses unique-identifier;
+    }
+
+    grouping account {
+      uses unique-identifier;
+    }
+
+    grouping tenant-root {
+      uses unique-identifier;
+    }
+
+    grouping service {
+      uses unique-identifier;
+    }
+
+    grouping controller-slice-privilege {
+      uses unique-identifier;
+    }
+
+    grouping site-credential {
+      uses unique-identifier;
+    }
+
+    grouping deployment-privilege {
+      uses unique-identifier;
+    }
+
+    grouping network-parameter-type {
+      uses unique-identifier;
+    }
+
+    grouping provider {
+      uses unique-identifier;
+    }
+
+    grouping tenant-with-container {
+      uses unique-identifier;
+    }
+
+    grouping deployment-role {
+      uses unique-identifier;
+    }
+
+    grouping project {
+      uses unique-identifier;
+    }
+
+    grouping tenant-root-privilege {
+      uses unique-identifier;
+    }
+
+    grouping slice-tag {
+      uses unique-identifier;
+    }
+
+    grouping coarse-tenant {
+      uses unique-identifier;
+    }
+
+    grouping router {
+      uses unique-identifier;
+    }
+
+    grouping service-resource {
+      uses unique-identifier;
+    }
+
+    grouping service-privilege {
+      uses unique-identifier;
+    }
+  }
+}