diff --git a/storage/storage.lisp b/storage/storage.lisp
index fd2baae..55b69b7 100644
--- a/storage/storage.lisp
+++ b/storage/storage.lisp
@@ -5,12 +5,13 @@
 (defpackage :scopes/storage
   (:use :common-lisp)
   (:local-nicknames (:config :scopes/config)
+                    (:core :scopes/core)
                     (:alx :alexandria))
   (:export #:config
            #:*db-config*
            #:make-engine #:make-storage #:engine
            #:timestamp-to-sql
-           #:db-options #:db-params #:qualified-table-name
+           #:params #:db-options #:db-params #:qualified-table-name
            #:do-sql #:query #:drop-table
            #:schema
            #:normalize-keyword #:normalize-plist))
@@ -21,7 +22,10 @@
 
 (defclass config (config:base)
   ((config:env-slots :initform '(db-name db-user db-password))
-   (db-config :reader db-config :initarg :db-config)))
+   (db-config :reader db-config :initarg :db-config)    ;to be replaced
+   (backend)
+   (db-type)
+   (connect-args)))
 
 ;;;; db configurations
 
@@ -32,8 +36,8 @@
   '(:postgres db-engine-pg))
 
 (defvar *db-params*
-  '(:sqlite3 (:id-type integer :json-type json)
-    :postgres (:id-type bigserial :json-type jsonb)))
+  '(:sqlite3 (:id-type integer :json-type json :ts-sql #'identity)
+    :postgres (:id-type bigserial :json-type jsonb :ts-sql #'ts-string)))
 
 (defclass db-engine ()
   ((connect :initarg :connect)
@@ -48,8 +52,15 @@
 (defgeneric timestamp-to-sql (engine ts)
   (:method ((engine db-engine) ts) ts))
 
+;;;; context and storage classes
+
+(defclass context (core:context)
+  ((storage :reader storage :initarg :storage)))
+
 (defclass storage ()
   ((engine :reader engine :initarg :engine)
+   (connect :reader connect :initarg :connect)
+   (params :reader params :initarg :params)
    (conn :reader conn)
    (schema :accessor schema)))
 
@@ -66,6 +77,8 @@
   (let ((config (config (engine st))))
     (getf config :options)))
 
+;;;; database (SQL) interface
+
 (defun qualified-table-name (st tn)
   (let ((schema (schema st)))
     (if schema
@@ -122,5 +135,7 @@
 (defclass db-engine-pg (db-engine) ())
 
 (defmethod timestamp-to-sql ((engine db-engine-pg) ts)
-  (format nil "~a" (local-time:universal-to-timestamp ts)))
+  (ts-string ts))
 
+(defun ts-string (ts)
+  (format nil "~a" (local-time:universal-to-timestamp ts)))
diff --git a/storage/tracking.lisp b/storage/tracking.lisp
index a2ff0e0..569c019 100644
--- a/storage/tracking.lisp
+++ b/storage/tracking.lisp
@@ -24,6 +24,9 @@
 (defun engine (tr)
   (storage:engine (storage (container tr))))
 
+(defun timestamp-to-sql (tr ts)
+  (funcall (getf (params (storage (container tr))) :ts-sql) ts))
+
 (defclass container ()
   ((item-factory :initform #'(lambda (cont head) 
                                (make-instance 'track :container cont :head head)))