diff --git a/src/copy/en.js b/src/copy/en.js
index ef50d69..8c3350b 100644
--- a/src/copy/en.js
+++ b/src/copy/en.js
@@ -5,7 +5,8 @@ export default {
     onlyTab: 'You cannot query a tab directly. The URL needs to be in the format /:sheet/:tab/:resource.',
     noSheet: sheet => `The sheet ${sheet} is not available in this server.`,
     noResource: prts => `The resource '${prts[2]}' does not exists in the tab '${prts[1]}' in this sheet.`,
-    noFragment: prts => `Fragment index does not exist`
+    noFragment: prts => `Fragment index does not exist`,
+    modelLayer: prts => `Something went wrong at the model layer`
   },
   success: {
     update: 'All sheets updated'
diff --git a/src/lib/errors.js b/src/lib/errors.js
new file mode 100644
index 0000000..d15b7f0
--- /dev/null
+++ b/src/lib/errors.js
@@ -0,0 +1,13 @@
+import copy from '../copy/en'
+
+export function modelLayerGeneric (parts) {
+  return new Error(copy.errors.modelLayer(parts))
+}
+
+export function noFragment (parts) {
+  return new Error(copy.errors.noFragment(parts))
+}
+
+export function noResource (parts) {
+  return new Error(copy.errors.noResource(parts))
+}
diff --git a/src/models/Interface.js b/src/models/Interface.js
index 60f98dd..71854fc 100644
--- a/src/models/Interface.js
+++ b/src/models/Interface.js
@@ -1,30 +1,41 @@
 /* eslint-disable */
 /**
- * Model is a class whose sole responsibility is to save and load blueprints.
- * It allows for different storage mechanisms for different kinds of blueprints.
+ * Model is a class whose sole responsibility is to save and load data through a custom URL format.
+ * As an interfacce, it allows for different storage mechanisms, and different scale/performance for different kinds of data.
  * 
  * ERRORS:
  * When a load function fails, it should throw either:
- * 1. A __ error if the resource doesn't exist on that sheet/tab.
- * 2. A __ error if a fragment lookup fails because it doesn't exist.
- * 3. A __ error if something else goes wrong.
+ * 1. noResource(parts) if the resource doesn't exist on that sheet/tab.
+ * 2. noFragment(parts) if a fragment lookup fails because it doesn't exist.
+ * 3. modelLayerGeneric(parts) if something else goes wrong.
+ *
+ * This is a WIP layer. See StoreJson.js for an example in action.
  */
 class Model {
   /**
-   * save - save a Blueprint, using the information it contains.
-   *
-   * @param  {type} blueprint the Blueprint to be saved.
-   * @return {type} Promise   which returns True.
+   * Index the data stored by this model, returning a list of the available URLs. 
+   * @return {Promise(boolean)} Unpacks to a list of available URLs if successful, throws an error otherwise.
    */
-  save (blueprint) {}
+  index () {}
+  
+  /**
+   * Save data at a URL. The URL is in the format
+   *    /:fetcherID/:tab/:resource
+   * Fetcher IDs must be unique, tabs and resources can be duplicated across
+   * different fetchers.
+   * 
+   * @param  {string} url - the URL at which to save the data.
+   * @param  {object} data - the data to be saved.
+   * @return {Promise(boolean)} Unpacks to true if the update was successful, false if otherwise.
+   */
+  save (url, data) {}
 
   /**
-   * load - load a resource from a data model, using a Blueprint object as
-   * well as a REST-like  URL of the format /:source/:tab/:resource.
-   *
-   * @param  {type} url       String that represents the path to resource.
-   * @param  {type} blueprint Blueprint object (desaturated?).
-   * @return {type}           Object containing the resource data.
+   * Load data from a URL, in the format
+   *    /:fetcherID/:tab/:resource
+   * 
+   * @param  {string} url - the URL at which to load the data.
+   * @return {Promise(object)} a Promise that unpacks to the data retrieved. An error will be thrown if the URL is invalid.
    */
-  load (url, blueprint) {}
+  load (url) {}
 }
diff --git a/src/models/StoreJson.js b/src/models/StoreJson.js
index 1124960..72ca593 100644
--- a/src/models/StoreJson.js
+++ b/src/models/StoreJson.js
@@ -1,5 +1,5 @@
 import fs from 'mz/fs'
-import copy from '../copy/en'
+import errors from '../lib/errors'
 
 const STORAGE_DIRNAME = 'temp'
 
@@ -45,7 +45,7 @@ class StoreJson {
             if (!isNaN(id) && id >= 0 && id < data.length) {
               return data[id]
             } else {
-              throw new Error(copy.errors.noFragment(parts))
+              throw errors.noFragment(parts)
             }
           } else {
             // Do a lookup if fragment is included to filter a relevant item
@@ -53,12 +53,12 @@ class StoreJson {
             if (!isNaN(index) && index >= 0 && index < data.length) {
               return data.filter((vl, idx) => idx === index)[0]
             } else {
-              throw new Error(copy.errors.noFragment(parts))
+              throw errors.noFragment(parts)
             }
           }
         })
     } else {
-      return Promise.reject(new Error(copy.errors.noResource(parts)))
+      return Promise.reject(errors.noResource(parts))
     }
   }