diff --git a/common/db.go b/common/db.go
index f20dbab..a5cf1c1 100644
--- a/common/db.go
+++ b/common/db.go
@@ -19,20 +19,12 @@ import (
 type DataTyp uint16
 
 const (
-	// TODO: Seems unused
-	DATA_ACCOUNT DataTyp = iota
-	// TODO: Seems unused, only read not written
-	DATA_ACCOUNT_CREATED
 	// API Tracking id to follow status of account creation
-	DATA_TRACKING_ID
+	DATA_TRACKING_ID = iota
 	// EVM address returned from API on account creation
 	DATA_PUBLIC_KEY
-	// TODO: Seems unused
-	DATA_CUSTODIAL_ID
 	// Currently active PIN used to authenticate ussd state change requests
 	DATA_ACCOUNT_PIN
-	// TODO: Seems unused
-	DATA_ACCOUNT_STATUS
 	// The first name of the user
 	DATA_FIRST_NAME
 	// The last name of the user
@@ -75,7 +67,10 @@ const (
 	// List of voucher EVM addresses for vouchers valid in the user context.
 	DATA_VOUCHER_ADDRESSES
 	// List of senders for valid transactions in the user context.
-	DATA_TX_SENDERS
+)
+
+const (
+	DATA_TX_SENDERS = 512 + iota
 	// List of recipients for valid transactions in the user context.
 	DATA_TX_RECIPIENTS
 	// List of voucher values for valid transactions in the user context.
diff --git a/doc/data.md b/doc/data.md
new file mode 100644
index 0000000..7a41f0c
--- /dev/null
+++ b/doc/data.md
@@ -0,0 +1,28 @@
+# Internals
+
+## Version
+
+This document describes component versions:
+
+* `urdt-ussd` `v0.5.0-beta`
+* `go-vise` `v0.2.2`
+
+
+## User profile data
+
+All user profile items are stored under keys matching the user's session id, prefixed with the 8-bit value `git.defalsify.org/vise.git/db.DATATYPE_USERDATA` (32), and followed with a 16-big big-endian value subprefix.
+
+For example, given the sessionId `+254123` and the key `git.grassecon.net/urdt-ussd/common.DATA_PUBLIC_KEY` (2) will be stored under the key:
+
+```
+0x322b3235343132330002
+
+prefix   sessionid       subprefix
+32       2b323534313233  0002
+```
+
+### Sub-prefixes
+
+All sub-prefixes are defined as constants in the `git.grassecon.net/urdt-ussd/common` package. The constant names have the prefix `DATA_`
+
+Please refer to inline godoc documentation for the `git.grassecon.net/urdt-ussd/common` package for details on each data item.