diff --git a/platformio.ini b/platformio.ini
index 2dd0f64..6525dc6 100644
--- a/platformio.ini
+++ b/platformio.ini
@@ -36,6 +36,7 @@ build_flags =
     -D TS_64BIT_TYPES_SUPPORT=1
     -D TS_DECFRAC_TYPE_SUPPORT=1
     -D TS_BYTE_STRING_TYPE_SUPPORT=1
+    -D TS_NESTED_JSON=1
 
 # include src directory (otherwise unit-tests will only include lib directory)
 test_build_project_src = true
diff --git a/src/thingset.c b/src/thingset.c
index 45baac1..b5e450a 100644
--- a/src/thingset.c
+++ b/src/thingset.c
@@ -65,11 +65,17 @@ int ts_process(struct ts_context *ts, const uint8_t *request, size_t request_len
     }
 }
 
-void ts_set_authentication(struct ts_context *ts, uint16_t flags)
+void ts_set_authentication(struct ts_context *ts, uint8_t flags)
 {
     ts->_auth_flags = flags;
 }
 
+void ts_set_update_callback(struct ts_context *ts, const uint16_t subsets, void (*update_cb)(void))
+{
+    ts->_update_subsets = subsets;
+    ts->update_cb = update_cb;
+}
+
 struct ts_data_object *ts_get_object_by_name(struct ts_context *ts, const char *name,
                                              size_t len, int32_t parent)
 {
diff --git a/src/thingset.h b/src/thingset.h
index b59b154..3601b89 100644
--- a/src/thingset.h
+++ b/src/thingset.h
@@ -341,15 +341,15 @@ static inline void *ts_array_to_void(struct ts_array_info *ptr) { return (void *
 #define TS_ROLE_EXP     (1U << 1)       // expert user
 #define TS_ROLE_MKR     (1U << 2)       // maker
 
-#define TS_READ_MASK    0x00FF          // read flags stored in 4 least-significant bits
-#define TS_WRITE_MASK   0xFF00          // write flags stored in 4 most-significant bits
+#define TS_READ_MASK    0x0F          // read flags stored in 4 least-significant bits
+#define TS_WRITE_MASK   0xF0          // write flags stored in 4 most-significant bits
 
-#define TS_USR_MASK     (TS_ROLE_USR << 8 | TS_ROLE_USR)
-#define TS_EXP_MASK     (TS_ROLE_EXP << 8 | TS_ROLE_EXP)
-#define TS_MKR_MASK     (TS_ROLE_MKR << 8 | TS_ROLE_MKR)
+#define TS_USR_MASK     (TS_ROLE_USR << 4 | TS_ROLE_USR)
+#define TS_EXP_MASK     (TS_ROLE_EXP << 4 | TS_ROLE_EXP)
+#define TS_MKR_MASK     (TS_ROLE_MKR << 4 | TS_ROLE_MKR)
 
 #define TS_READ(roles)          ((roles) & TS_READ_MASK)
-#define TS_WRITE(roles)         (((roles) << 8) & TS_WRITE_MASK)
+#define TS_WRITE(roles)         (((roles) << 4) & TS_WRITE_MASK)
 #define TS_READ_WRITE(roles)    (TS_READ(roles) | TS_WRITE(roles))
 
 #define TS_USR_R        TS_READ(TS_ROLE_USR)
@@ -401,24 +401,30 @@ struct ts_data_object {
     /**
      * One of TS_TYPE_INT32, _FLOAT, ...
      */
-    const uint8_t type;
+    const uint32_t type : 4;
 
     /**
-     * Exponent (10^exponent = factor to convert to SI unit) for decimal fraction type,
-     * decimal digits to use for printing of floats in JSON strings or
-     * length of string buffer for string type
+     * Variable storing different detail information depending on th data type
+     *
+     * - FLOAT32: Decimal digits (precision) to use for printing in JSON strings.
+     *
+     * - DECFRAC: Exponent (10^exponent = factor to convert to internal unit). Example: If
+     *   a voltage measurement is internally stored as an integer in mV, use exponent -3 to
+     *   convert to the SI base unit V as exposed via ThingSet.
+     *
+     * - STRING or BYTES: Size of the internal buffer in bytes.
      */
-    const int16_t detail;
+    const int32_t detail : 12;
 
     /**
      * Flags to define read/write access
      */
-    const uint16_t access;
+    const uint32_t access : 8;
 
     /**
      * Flags to assign data item to different data item subsets (e.g. for publication messages)
      */
-    uint16_t subsets;
+    uint32_t subsets : 8;
 
 };
 
@@ -479,7 +485,18 @@ struct ts_context {
     /**
      * Stores current authentication status (authentication as "normal" user as default)
      */
-    uint16_t _auth_flags;
+    uint8_t _auth_flags;
+
+    /**
+     * Stores current authentication status (authentication as "normal" user as default)
+     */
+    uint8_t _update_subsets;
+
+    /**
+     * Callback to be called from patch function if a value belonging to _update_subsets
+     * was changed
+     */
+    void (*update_cb)(void);
 };
 
 /**
@@ -529,7 +546,16 @@ void ts_dump_json(struct ts_context *ts, ts_object_id_t obj_id, int level);
  * @param ts Pointer to ThingSet context.
  * @param flags Flags to define authentication level (1 = access allowed)
  */
-void ts_set_authentication(struct ts_context *ts, uint16_t flags);
+void ts_set_authentication(struct ts_context *ts, uint8_t flags);
+
+/**
+ * Configures a callback for notification if data belonging to specified subset(s) was updated.
+ *
+ * @param ts Pointer to ThingSet context.
+ * @param subsets Flags to select which subset(s) of data items should be considered
+ * @param update_cb Callback to be called after an update.
+ */
+void ts_set_update_callback(struct ts_context *ts, const uint16_t subsets, void (*update_cb)(void));
 
 /**
  * Retrieve data in JSON format for given subset(s).
@@ -676,7 +702,7 @@ int ts_bin_pub_can(struct ts_context *ts, int *start_pos, uint16_t subset, uint8
  *
  * @returns ThingSet status code
  */
-int ts_bin_import(struct ts_context *ts, uint8_t *data, size_t len, uint16_t auth_flags,
+int ts_bin_import(struct ts_context *ts, uint8_t *data, size_t len, uint8_t auth_flags,
                   uint16_t subsets);
 
 /**
@@ -760,11 +786,16 @@ class ThingSet
         ts_dump_json(&ts, obj_id, level);
     };
 
-    inline void set_authentication(uint16_t flags)
+    inline void set_authentication(uint8_t flags)
     {
         ts_set_authentication(&ts, flags);
     };
 
+    inline void set_update_callback(const uint16_t subsets, void (*update_cb)(void))
+    {
+        ts_set_update_callback(&ts, subsets, update_cb);
+    };
+
     inline int txt_export(char *buf, size_t size, const uint16_t subsets)
     {
         return ts_txt_export(&ts, buf, size, subsets);
@@ -790,7 +821,7 @@ class ThingSet
         return ts_bin_export(&ts, buf, size, subsets);
     };
 
-    inline int bin_import(uint8_t *buf, size_t size, uint16_t auth_flags, const uint16_t subsets)
+    inline int bin_import(uint8_t *buf, size_t size, uint8_t auth_flags, const uint16_t subsets)
     {
         return ts_bin_import(&ts, buf, size, auth_flags, subsets);
     };
@@ -880,7 +911,7 @@ class ThingSet
      *
      * @returns ThingSet status code
      */
-    inline int bin_sub(uint8_t *cbor_data, size_t len, uint16_t auth_flags, uint16_t subsets)
+    inline int bin_sub(uint8_t *cbor_data, size_t len, uint8_t auth_flags, uint16_t subsets)
         __attribute__((deprecated))
     {
         return ts_bin_import(&ts, cbor_data + 1, len - 1, auth_flags, subsets);
diff --git a/src/thingset_bin.c b/src/thingset_bin.c
index a7aca59..c47d5a1 100644
--- a/src/thingset_bin.c
+++ b/src/thingset_bin.c
@@ -345,7 +345,7 @@ int ts_bin_fetch(struct ts_context *ts, const struct ts_data_object *parent, uin
     }
 }
 
-int ts_bin_import(struct ts_context *ts, uint8_t *data, size_t len, uint16_t auth_flags,
+int ts_bin_import(struct ts_context *ts, uint8_t *data, size_t len, uint8_t auth_flags,
                   uint16_t subsets)
 {
     uint8_t resp_tmp[1] = {};   // only one character as response expected
@@ -358,10 +358,11 @@ int ts_bin_import(struct ts_context *ts, uint8_t *data, size_t len, uint16_t aut
 }
 
 int ts_bin_patch(struct ts_context *ts, const struct ts_data_object *parent,
-                 unsigned int pos_payload, uint16_t auth_flags, uint16_t subsets)
+                 unsigned int pos_payload, uint8_t auth_flags, uint16_t subsets)
 {
     unsigned int pos_req = pos_payload;
     uint16_t num_elements, element = 0;
+    bool updated = false;
 
     if ((ts->req[pos_req] & CBOR_TYPE_MASK) != CBOR_MAP) {
         return ts_bin_response(ts, TS_STATUS_BAD_REQUEST);
@@ -403,6 +404,9 @@ int ts_bin_patch(struct ts_context *ts, const struct ts_data_object *parent,
             else {
                 // actually deserialize the data and update object
                 num_bytes = cbor_deserialize_data_obj(&ts->req[pos_req], object);
+                if (ts->_update_subsets & object->subsets) {
+                    updated = true;
+                }
             }
         }
         else {
@@ -425,6 +429,9 @@ int ts_bin_patch(struct ts_context *ts, const struct ts_data_object *parent,
     }
 
     if (element == num_elements) {
+        if (updated && ts->update_cb != NULL) {
+            ts->update_cb();
+        }
         return ts_bin_response(ts, TS_STATUS_CHANGED);
     } else {
         return ts_bin_response(ts, TS_STATUS_BAD_REQUEST);
diff --git a/src/thingset_priv.h b/src/thingset_priv.h
index 562036d..c6bb9d8 100644
--- a/src/thingset_priv.h
+++ b/src/thingset_priv.h
@@ -114,7 +114,7 @@ int ts_txt_patch(struct ts_context *ts,  const struct ts_data_object *parent);
  * @param subsets Bitset to specifiy data item subsets to be considered, 0 to ignore
  */
 int ts_bin_patch(struct ts_context *ts, const struct ts_data_object *parent,
-                 unsigned int pos_payload, uint16_t auth_flags, uint16_t subsets);
+                 unsigned int pos_payload, uint8_t auth_flags, uint16_t subsets);
 
 /**
  * POST request to append data.
diff --git a/src/thingset_txt.c b/src/thingset_txt.c
index 1ebb920..d8dd819 100644
--- a/src/thingset_txt.c
+++ b/src/thingset_txt.c
@@ -163,7 +163,21 @@ int ts_json_serialize_value(struct ts_context *ts, char *buf, size_t size,
         pos = snprintf(&buf[pos], size - pos, "[");
         for (unsigned int i = 0; i < ts->num_objects; i++) {
             if (ts->data_objects[i].subsets & (uint16_t)object->detail) {
+#if TS_NESTED_JSON
+                if (ts->data_objects[i].parent == 0) {
+                    pos += snprintf(&buf[pos], size - pos, "\"%s\",", ts->data_objects[i].name);
+                }
+                else {
+                    struct ts_data_object *parent_obj =
+                        ts_get_object_by_id(ts, ts->data_objects[i].parent);
+                    if (parent_obj != NULL) {
+                        pos += snprintf(&buf[pos], size - pos, "\"%s/%s\",",
+                                        parent_obj->name, ts->data_objects[i].name);
+                    }
+                }
+#else
                 pos += snprintf(&buf[pos], size - pos, "\"%s\",", ts->data_objects[i].name);
+#endif
             }
         }
         if (pos > 1) {
@@ -502,6 +516,7 @@ int ts_json_deserialize_value(struct ts_context *ts, char *buf, size_t len, jsmn
 int ts_txt_patch(struct ts_context *ts, const struct ts_data_object *parent)
 {
     int tok = 0;       // current token
+    bool updated = false;
 
     // buffer for data object value (largest negative 64bit integer has 20 digits)
     char value_buf[21];
@@ -598,6 +613,14 @@ int ts_txt_patch(struct ts_context *ts, const struct ts_data_object *parent)
 
         tok += ts_json_deserialize_value(ts, &ts->json_str[ts->tokens[tok].start], value_len,
             ts->tokens[tok].type, object);
+
+        if (ts->_update_subsets & object->subsets) {
+            updated = true;
+        }
+    }
+
+    if (updated && ts->update_cb != NULL) {
+        ts->update_cb();
     }
 
     return ts_txt_response(ts, TS_STATUS_CHANGED);
@@ -683,10 +706,15 @@ int ts_txt_create(struct ts_context *ts, const struct ts_data_object *object)
     }
     else if (object->type == TS_T_SUBSET) {
         if (ts->tokens[0].type == JSMN_STRING) {
-            struct ts_data_object *del_object = ts_get_object_by_name(ts, ts->json_str +
+#if TS_NESTED_JSON
+            struct ts_data_object *add_object = ts_get_object_by_path(ts, ts->json_str +
+                ts->tokens[0].start, ts->tokens[0].end - ts->tokens[0].start);
+#else
+            struct ts_data_object *add_object = ts_get_object_by_name(ts, ts->json_str +
                 ts->tokens[0].start, ts->tokens[0].end - ts->tokens[0].start, -1);
-            if (del_object != NULL) {
-                del_object->subsets |= (uint16_t)object->detail;
+#endif
+            if (add_object != NULL) {
+                add_object->subsets |= (uint16_t)object->detail;
                 return ts_txt_response(ts, TS_STATUS_CREATED);
             }
             return ts_txt_response(ts, TS_STATUS_NOT_FOUND);
@@ -708,8 +736,13 @@ int ts_txt_delete(struct ts_context *ts, const struct ts_data_object *object)
     }
     else if (object->type == TS_T_SUBSET) {
         if (ts->tokens[0].type == JSMN_STRING) {
+#if TS_NESTED_JSON
+            struct ts_data_object *del_object = ts_get_object_by_path(ts, ts->json_str +
+                ts->tokens[0].start, ts->tokens[0].end - ts->tokens[0].start);
+#else
             struct ts_data_object *del_object = ts_get_object_by_name(ts, ts->json_str +
                 ts->tokens[0].start, ts->tokens[0].end - ts->tokens[0].start, -1);
+#endif
             if (del_object != NULL) {
                 del_object->subsets &= ~((uint16_t)object->detail);
                 return ts_txt_response(ts, TS_STATUS_DELETED);
@@ -769,6 +802,49 @@ int ts_txt_exec(struct ts_context *ts, const struct ts_data_object *object)
     return ts_txt_response(ts, TS_STATUS_VALID);
 }
 
+#if TS_NESTED_JSON
+
+/* currently only supporting nesting of depth 1 */
+int ts_txt_export(struct ts_context *ts, char *buf, size_t buf_size, uint16_t subsets)
+{
+    unsigned int len = 1;
+    buf[0] = '{';
+    uint16_t prev_parent = 0;
+    unsigned int depth = 0;
+
+    for (unsigned int i = 0; i < ts->num_objects; i++) {
+        if (ts->data_objects[i].subsets & subsets) {
+            const uint16_t parent_id = ts->data_objects[i].parent;
+            if (prev_parent != parent_id) {
+                if (prev_parent != 0) {
+                    // close object of previous parent
+                    buf[len-1] = '}';    // overwrite comma
+                    buf[len++] = ',';
+                }
+                struct ts_data_object *parent = ts_get_object_by_id(ts, parent_id);
+                len += snprintf(&buf[len], buf_size - len, "\"%s\":{", parent->name);
+                prev_parent = parent_id;
+                depth = 1;
+            }
+            len += ts_json_serialize_name_value(ts, &buf[len], buf_size - len,
+                &ts->data_objects[i]);
+        }
+        if (len >= buf_size - 1 - depth) {
+            return 0;
+        }
+    }
+
+    buf[len-1] = '}';    // overwrite comma
+
+    if (depth == 1) {
+        buf[len++] = '}';
+    }
+
+    return len;
+}
+
+#else
+
 int ts_txt_export(struct ts_context *ts, char *buf, size_t buf_size, uint16_t subsets)
 {
     unsigned int len = 1;
@@ -789,6 +865,8 @@ int ts_txt_export(struct ts_context *ts, char *buf, size_t buf_size, uint16_t su
     return len;
 }
 
+#endif /* TS_NESTED_JSON */
+
 int ts_txt_statement(struct ts_context *ts, char *buf, size_t buf_size,
                      struct ts_data_object *object)
 {
diff --git a/src/ts_config.h b/src/ts_config.h
index 7f81927..42f432c 100644
--- a/src/ts_config.h
+++ b/src/ts_config.h
@@ -75,4 +75,24 @@
 #define TS_BYTE_STRING_TYPE_SUPPORT CONFIG_THINGSET_BYTE_STRING_TYPE_SUPPORT
 #endif
 
+/*
+ * The ThingSet specification v0.5 introduces a different data layout compared to previous
+ * versions where the data is grouped by entities of the device (like battery, actuator)
+ * instead of the data type (e.g. measurement, configuration). The data type is described by
+ * a single character prefix in the item name.
+ * The new grouping allows to have same item names in different groups, so for unambigous
+ * description of the data the nested structure has to be maintained in statements.
+ *
+ * With nested JSON enabled, requesting names for IDs will also return the entire path (as
+ * a JSON pointer) instead of just the data item name.
+ *
+ * This option is introduced to maintain compatibility with legacy firmware and will be
+ * enabled by default in the future.
+ */
+#if !defined(TS_NESTED_JSON) && !defined(CONFIG_THINGSET_NESTED_JSON)
+#define TS_NESTED_JSON 0        // default: no nested JSON for legacy code
+#elif !defined(TS_NESTED_JSON)
+#define TS_NESTED_JSON CONFIG_THINGSET_NESTED_JSON
+#endif
+
 #endif /* TS_CONFIG_H_ */
diff --git a/test/main.cpp b/test/main.cpp
index 7935e22..0edfaaa 100644
--- a/test/main.cpp
+++ b/test/main.cpp
@@ -55,7 +55,7 @@ void tests_text_mode()
     RUN_TEST(test_txt_patch_readonly);
     RUN_TEST(test_txt_patch_wrong_path);
     RUN_TEST(test_txt_patch_unknown_object);
-    RUN_TEST(test_txt_conf_callback);
+    RUN_TEST(test_txt_group_callback);
 
     // POST request
     RUN_TEST(test_txt_exec);
@@ -81,6 +81,9 @@ void tests_text_mode()
     // data export
     RUN_TEST(test_txt_export);
 
+    // update notification
+    RUN_TEST(test_txt_update_callback),
+
     UNITY_END();
 }
 
@@ -128,6 +131,9 @@ void tests_binary_mode()
     RUN_TEST(test_bin_export);
     RUN_TEST(test_bin_import);
 
+    // update notification
+    RUN_TEST(test_bin_update_callback),
+
     UNITY_END();
 }
 
diff --git a/test/test.h b/test/test.h
index a8be964..e488709 100644
--- a/test/test.h
+++ b/test/test.h
@@ -36,6 +36,7 @@ extern "C" {
 
 #define SUBSET_REPORT  (1U << 0)   // report subset of data items for publication
 #define SUBSET_CAN     (1U << 1)   // data nodes used for CAN bus publication messages
+#define SUBSET_NVM     (1U << 2)   // data that should be stored in EEPROM
 
 extern char manufacturer[];
 extern bool pub_report_enable;
@@ -69,13 +70,15 @@ extern struct ts_context ts;
 extern uint8_t req_buf[TS_REQ_BUFFER_LEN];
 extern uint8_t resp_buf[TS_RESP_BUFFER_LEN];
 
-extern bool conf_callback_called;
+extern bool group_callback_called;
+extern bool update_callback_called;
 extern bool dummy_called_flag;
 extern struct ts_array_info pub_serial_array;
 
 /* Helper functions (see test_context.c) */
 void dummy(void);
-void conf_callback(void);
+void group_callback(void);
+void update_callback(void);
 void reset_function(void);
 void auth_function(void);
 int _hex2bin(uint8_t *bin, size_t bin_size, const char *hex);
@@ -142,7 +145,7 @@ void test_txt_patch_array(void);
 void test_txt_patch_readonly(void);
 void test_txt_patch_wrong_path(void);
 void test_txt_patch_unknown_object(void);
-void test_txt_conf_callback(void);
+void test_txt_group_callback(void);
 void test_txt_exec(void);
 void test_txt_statement_subset(void);
 void test_txt_statement_group(void);
@@ -157,6 +160,7 @@ void test_txt_auth_reset(void);
 void test_txt_wrong_command(void);
 void test_txt_get_endpoint(void);
 void test_txt_export(void);
+void test_txt_update_callback(void);
 
 void test_bin_get_meas_ids_values(void);
 void test_bin_get_meas_names_values(void);
@@ -180,6 +184,7 @@ void test_bin_deserialize_bytes(void);
 void test_bin_patch_fetch_bytes(void);
 void test_bin_export(void);
 void test_bin_import(void);
+void test_bin_update_callback(void);
 
 #ifdef __cplusplus
 } /* extern "C" */
diff --git a/test/test_bin.c b/test/test_bin.c
index 4ed420c..f10b3bb 100644
--- a/test/test_bin.c
+++ b/test/test_bin.c
@@ -206,7 +206,8 @@ void test_bin_patch_rounded_float(void)
             0x05
     };
     const uint8_t resp_expected[] = {
-        TS_STATUS_CHANGED };
+        TS_STATUS_CHANGED
+    };
 
     TEST_ASSERT_BIN_REQ_EXP_BIN(req, sizeof(req), resp_expected, sizeof(resp_expected));
 
@@ -238,9 +239,8 @@ void test_bin_statement_group(void)
     const char resp_expected[] =
         "1F "
         "01 "                                       // ID of "info"
-        "83 "                                       // array with 3 elements
+        "82 "                                       // array with 2 elements
         "6B 4C 69 62 72 65 20 53 6F 6C 61 72 "      // "Libre Solar"
-        "1A 00 BC 61 4E "                           // int 12345678
         "68 41 42 43 44 31 32 33 34 ";              // "ABCD1234"
 
     int resp_len = ts_bin_statement_by_path(&ts, resp_buf, sizeof(resp_buf), "info");
@@ -428,7 +428,7 @@ void test_bin_export(void)
 {
     const char resp_expected[] =
         "A4 "                       // map with 4 elements
-        "18 1A 1A 00 BC 61 4E "     // int 12345678
+        "10 1A 00 BC 61 4E "        // int 12345678
         "18 71 FA 41 61 99 9a "     // float 14.10
         "18 72 FA 40 a4 28 f6 "     // float 5.13
         "18 73 16 ";                // int 22
@@ -437,3 +437,29 @@ void test_bin_export(void)
 
     TEST_ASSERT_BIN_RESP(resp_buf, resp_len, resp_expected);
 }
+
+void test_bin_update_callback(void)
+{
+    const uint8_t req[] = {
+        TS_PATCH,
+        0x18, ID_CONF,
+        0xA1,
+            0x18, 0x31,
+            0x05
+    };
+    const uint8_t resp_expected[] = {
+        TS_STATUS_CHANGED
+    };
+
+    update_callback_called = false;
+
+    // without callback
+    ts_set_update_callback(&ts, SUBSET_NVM, NULL);
+    TEST_ASSERT_BIN_REQ_EXP_BIN(req, sizeof(req), resp_expected, sizeof(resp_expected));
+    TEST_ASSERT_EQUAL(false, update_callback_called);
+
+    // with configured callback
+    ts_set_update_callback(&ts, SUBSET_NVM, update_callback);
+    TEST_ASSERT_BIN_REQ_EXP_BIN(req, sizeof(req), resp_expected, sizeof(resp_expected));
+    TEST_ASSERT_EQUAL(true, update_callback_called);
+}
diff --git a/test/test_context.c b/test/test_context.c
index 3efffce..40ad849 100644
--- a/test/test_context.c
+++ b/test/test_context.c
@@ -12,19 +12,25 @@ struct ts_context ts;
 uint8_t req_buf[TS_REQ_BUFFER_LEN];
 uint8_t resp_buf[TS_RESP_BUFFER_LEN];
 
-bool conf_callback_called;
+bool group_callback_called;
+bool update_callback_called;
 bool dummy_called_flag;
 struct ts_array_info pub_serial_array;
 
 
 void dummy(void)
 {
-    dummy_called_flag = 1;
+    dummy_called_flag = true;
 }
 
-void conf_callback(void)
+void group_callback(void)
 {
-    conf_callback_called = 1;
+    group_callback_called = true;
+}
+
+void update_callback(void)
+{
+    update_callback_called = true;
 }
 
 void reset_function()
diff --git a/test/test_data.c b/test/test_data.c
index 71ba011..e1c04fd 100644
--- a/test/test_data.c
+++ b/test/test_data.c
@@ -70,12 +70,11 @@ struct ts_array_info float32_array = {B, sizeof(B)/sizeof(float), 2, TS_T_FLOAT3
 uint8_t bytes[300] = {};
 struct ts_bytes_buffer bytes_buf = { bytes, 0 };
 
-void dummy(void);
-void conf_callback(void);
-
-
 struct ts_data_object data_objects[] = {
 
+    TS_ITEM_UINT32(0x10, "t_s", &timestamp,
+        ID_ROOT, TS_ANY_RW, SUBSET_REPORT),
+
     // DEVICE INFORMATION /////////////////////////////////////////////////////
 
     TS_GROUP(ID_INFO, "info", TS_NO_CALLBACK, ID_ROOT),
@@ -83,21 +82,18 @@ struct ts_data_object data_objects[] = {
     TS_ITEM_STRING(0x19, "Manufacturer", manufacturer, 0,
         ID_INFO, TS_ANY_R, 0),
 
-    TS_ITEM_UINT32(0x1A, "Timestamp_s", &timestamp,
-        ID_INFO, TS_ANY_RW, SUBSET_REPORT),
-
     TS_ITEM_STRING(0x1B, "DeviceID", device_id, sizeof(device_id),
-        ID_INFO, TS_ANY_R | TS_MKR_W, 0),
+        ID_INFO, TS_ANY_R | TS_MKR_W, SUBSET_NVM),
 
     // CONFIGURATION //////////////////////////////////////////////////////////
 
-    TS_GROUP(ID_CONF, "conf", &conf_callback, ID_ROOT),
+    TS_GROUP(ID_CONF, "conf", &group_callback, ID_ROOT),
 
     TS_ITEM_FLOAT(0x31, "BatCharging_V", &bat_charging_voltage, 2,
-        ID_CONF, TS_ANY_RW, 0),
+        ID_CONF, TS_ANY_RW, SUBSET_NVM),
 
     TS_ITEM_FLOAT(0x32, "LoadDisconnect_V", &load_disconnect_voltage, 2,
-        ID_CONF, TS_ANY_RW, 0),
+        ID_CONF, TS_ANY_RW, SUBSET_NVM),
 
     // INPUT DATA /////////////////////////////////////////////////////////////
 
diff --git a/test/test_shim.cpp b/test/test_shim.cpp
index 0d95ff7..f212e9a 100644
--- a/test/test_shim.cpp
+++ b/test/test_shim.cpp
@@ -9,6 +9,6 @@ void test_shim_get_object(void)
 {
     ThingSet ts(&data_objects[0], data_objects_size);
 
-    ThingSetDataObject *object = ts.get_object(ID_INFO);
+    ThingSetDataObject *object = ts.get_object(0x10);   // timestamp object "t_s"
     TEST_ASSERT_EQUAL_PTR(&data_objects[0], object);
 }
diff --git a/test/test_txt.c b/test/test_txt.c
index 508869a..7f8853a 100644
--- a/test/test_txt.c
+++ b/test/test_txt.c
@@ -96,13 +96,13 @@ void test_txt_patch_unknown_object(void)
     TEST_ASSERT_TXT_REQ("=conf {\"i3\" : 52}", ":A4 Not Found.");
 }
 
-void test_txt_conf_callback(void)
+void test_txt_group_callback(void)
 {
-    conf_callback_called = 0;
+    group_callback_called = false;
 
     TEST_ASSERT_TXT_REQ("=conf {\"i32\":52}", ":84 Changed.");
 
-    TEST_ASSERT_EQUAL(1, conf_callback_called);
+    TEST_ASSERT_EQUAL(true, group_callback_called);
 }
 
 void test_txt_exec(void)
@@ -114,26 +114,46 @@ void test_txt_exec(void)
     TEST_ASSERT_EQUAL(1, dummy_called_flag);
 }
 
+#if TS_NESTED_JSON
+
+void test_txt_statement_subset(void)
+{
+    const char expected[] = "#report {\"t_s\":12345678,"
+        "\"meas\":{\"Bat_V\":14.10,\"Bat_A\":5.13,\"Ambient_degC\":22}}";
+
+    int resp_len = ts_txt_statement_by_path(&ts, (char *)resp_buf, TS_RESP_BUFFER_LEN, "report");
+
+    TEST_ASSERT_TXT_RESP(resp_len, expected);
+
+    resp_len = ts_txt_statement_by_id(&ts, (char *)resp_buf, TS_RESP_BUFFER_LEN, ID_REPORT);
+
+    TEST_ASSERT_TXT_RESP(resp_len, expected);
+}
+
+#else
+
 void test_txt_statement_subset(void)
 {
     int resp_len = ts_txt_statement_by_path(&ts, (char *)resp_buf, TS_RESP_BUFFER_LEN, "report");
 
-    TEST_ASSERT_TXT_RESP(resp_len, "#report {\"Timestamp_s\":12345678,\"Bat_V\":14.10,\"Bat_A\":5.13,\"Ambient_degC\":22}");
+    TEST_ASSERT_TXT_RESP(resp_len, "#report {\"t_s\":12345678,\"Bat_V\":14.10,\"Bat_A\":5.13,\"Ambient_degC\":22}");
 
     resp_len = ts_txt_statement_by_id(&ts, (char *)resp_buf, TS_RESP_BUFFER_LEN, ID_REPORT);
 
-    TEST_ASSERT_TXT_RESP(resp_len, "#report {\"Timestamp_s\":12345678,\"Bat_V\":14.10,\"Bat_A\":5.13,\"Ambient_degC\":22}");
+    TEST_ASSERT_TXT_RESP(resp_len, "#report {\"t_s\":12345678,\"Bat_V\":14.10,\"Bat_A\":5.13,\"Ambient_degC\":22}");
 }
 
+#endif /* TS_NESTED_JSON */
+
 void test_txt_statement_group(void)
 {
     int resp_len = ts_txt_statement_by_path(&ts, (char *)resp_buf, TS_RESP_BUFFER_LEN, "info");
 
-    TEST_ASSERT_TXT_RESP(resp_len, "#info {\"Manufacturer\":\"Libre Solar\",\"Timestamp_s\":12345678,\"DeviceID\":\"ABCD1234\"}");
+    TEST_ASSERT_TXT_RESP(resp_len, "#info {\"Manufacturer\":\"Libre Solar\",\"DeviceID\":\"ABCD1234\"}");
 
     resp_len = ts_txt_statement_by_id(&ts, (char *)resp_buf, TS_RESP_BUFFER_LEN, ID_INFO);
 
-    TEST_ASSERT_TXT_RESP(resp_len, "#info {\"Manufacturer\":\"Libre Solar\",\"Timestamp_s\":12345678,\"DeviceID\":\"ABCD1234\"}");
+    TEST_ASSERT_TXT_RESP(resp_len, "#info {\"Manufacturer\":\"Libre Solar\",\"DeviceID\":\"ABCD1234\"}");
 }
 
 void test_txt_pub_list_channels(void)
@@ -150,20 +170,40 @@ void test_txt_pub_enable(void)
     TEST_ASSERT_TRUE(pub_report_enable);
 }
 
+#if TS_NESTED_JSON
+
+void test_txt_pub_delete_append_object(void)
+{
+    /* before change */
+    TEST_ASSERT_TXT_REQ("?report", ":85 Content. [\"t_s\",\"meas/Bat_V\",\"meas/Bat_A\",\"meas/Ambient_degC\"]");
+    /* delete "Ambient_degC" */
+    TEST_ASSERT_TXT_REQ("-report \"meas/Ambient_degC\"", ":82 Deleted.");
+    /* check if it was deleted */
+    TEST_ASSERT_TXT_REQ("?report", ":85 Content. [\"t_s\",\"meas/Bat_V\",\"meas/Bat_A\"]");
+    /* append "Ambient_degC" again */
+    TEST_ASSERT_TXT_REQ("+report \"meas/Ambient_degC\"", ":81 Created.");
+    /* check if it was appended */
+    TEST_ASSERT_TXT_REQ("?report", ":85 Content. [\"t_s\",\"meas/Bat_V\",\"meas/Bat_A\",\"meas/Ambient_degC\"]");
+}
+
+#else
+
 void test_txt_pub_delete_append_object(void)
 {
     /* before change */
-    TEST_ASSERT_TXT_REQ("?report", ":85 Content. [\"Timestamp_s\",\"Bat_V\",\"Bat_A\",\"Ambient_degC\"]");
+    TEST_ASSERT_TXT_REQ("?report", ":85 Content. [\"t_s\",\"Bat_V\",\"Bat_A\",\"Ambient_degC\"]");
     /* delete "Ambient_degC" */
     TEST_ASSERT_TXT_REQ("-report \"Ambient_degC\"", ":82 Deleted.");
     /* check if it was deleted */
-    TEST_ASSERT_TXT_REQ("?report", ":85 Content. [\"Timestamp_s\",\"Bat_V\",\"Bat_A\"]");
+    TEST_ASSERT_TXT_REQ("?report", ":85 Content. [\"t_s\",\"Bat_V\",\"Bat_A\"]");
     /* append "Ambient_degC" again */
     TEST_ASSERT_TXT_REQ("+report \"Ambient_degC\"", ":81 Created.");
     /* check if it was appended */
-    TEST_ASSERT_TXT_REQ("?report", ":85 Content. [\"Timestamp_s\",\"Bat_V\",\"Bat_A\",\"Ambient_degC\"]");
+    TEST_ASSERT_TXT_REQ("?report", ":85 Content. [\"t_s\",\"Bat_V\",\"Bat_A\",\"Ambient_degC\"]");
 }
 
+#endif /* TS_NESTED_JSON */
+
 void test_txt_auth_user(void)
 {
     /* authorize as expert user */
@@ -233,9 +273,41 @@ void test_txt_get_endpoint(void)
     TEST_ASSERT_EQUAL_UINT16(0xE1, object->id);
 }
 
+#if TS_NESTED_JSON
+
+void test_txt_export(void)
+{
+    const char expected[] =
+        "{\"t_s\":12345678,\"meas\":{\"Bat_V\":14.10,\"Bat_A\":5.13,\"Ambient_degC\":22}}";
+
+    int resp_len = ts_txt_export(&ts, (char *)resp_buf, TS_RESP_BUFFER_LEN, SUBSET_REPORT);
+    resp_buf[resp_len] = '\0';
+
+    TEST_ASSERT_TXT_RESP(resp_len, expected);
+}
+
+#else
+
 void test_txt_export(void)
 {
     int resp_len = ts_txt_export(&ts, (char *)resp_buf, TS_RESP_BUFFER_LEN, SUBSET_REPORT);
 
-    TEST_ASSERT_TXT_RESP(resp_len, "{\"Timestamp_s\":12345678,\"Bat_V\":14.10,\"Bat_A\":5.13,\"Ambient_degC\":22}");
+    TEST_ASSERT_TXT_RESP(resp_len, "{\"t_s\":12345678,\"Bat_V\":14.10,\"Bat_A\":5.13,\"Ambient_degC\":22}");
+}
+
+#endif /* TS_NESTED_JSON */
+
+void test_txt_update_callback(void)
+{
+    update_callback_called = false;
+
+    // without callback
+    ts_set_update_callback(&ts, SUBSET_NVM, NULL);
+    TEST_ASSERT_TXT_REQ("=conf {\"BatCharging_V\":52}", ":84 Changed.");
+    TEST_ASSERT_EQUAL(false, update_callback_called);
+
+    // with configured callback
+    ts_set_update_callback(&ts, SUBSET_NVM, update_callback);
+    TEST_ASSERT_TXT_REQ("=conf {\"BatCharging_V\":52}", ":84 Changed.");
+    TEST_ASSERT_EQUAL(true, update_callback_called);
 }
diff --git a/zephyr/Kconfig.thingset b/zephyr/Kconfig.thingset
index d744f28..5e3e0a7 100644
--- a/zephyr/Kconfig.thingset
+++ b/zephyr/Kconfig.thingset
@@ -58,6 +58,23 @@ config THINGSET_CPP_LEGACY
           ThingSet protocol library. Enable if your C++ code uses
           DataNode or ArrayInfo instead of ThingSetDataNode or ThingSetArrayInfo.
 
+config THINGSET_NESTED_JSON
+        bool "Use nested JSON for statements"
+        default n
+        help
+          The ThingSet specification v0.5 introduces a different data layout compared to previous
+          versions where the data is grouped by entities of the device (like battery, actuator)
+          instead of the data type (e.g. measurement, configuration). The data type is described by
+          a single character prefix in the item name.
+          The new grouping allows to have same item names in different groups, so for unambigous
+          description of the data the nested structure has to be maintained in statements.
+
+          With nested JSON enabled, requesting names for IDs will also return the entire path (as
+          a JSON pointer) instead of just the data item name.
+
+          This option is introduced to maintain compatibility with legacy firmware and will be
+          enabled by default in the future.
+
 module = THINGSET
 module-str = thingset
 source "subsys/logging/Kconfig.template.log_config"
diff --git a/zephyr/tests/src/main.c b/zephyr/tests/src/main.c
index ea0db66..759cab4 100644
--- a/zephyr/tests/src/main.c
+++ b/zephyr/tests/src/main.c
@@ -47,7 +47,7 @@ void test_main(void)
         ztest_unit_test_setup_teardown(test_txt_patch_readonly, setup, teardown),
         ztest_unit_test_setup_teardown(test_txt_patch_wrong_path, setup, teardown),
         ztest_unit_test_setup_teardown(test_txt_patch_unknown_object, setup, teardown),
-        ztest_unit_test_setup_teardown(test_txt_conf_callback, setup, teardown),
+        ztest_unit_test_setup_teardown(test_txt_group_callback, setup, teardown),
         /* Text mode: POST request */
         ztest_unit_test_setup_teardown(test_txt_exec, setup, teardown),
         /* Text mode: statements (pub/sub messages) */
@@ -66,6 +66,8 @@ void test_main(void)
         ztest_unit_test_setup_teardown(test_txt_get_endpoint, setup, teardown),
         /* Text mode: exporting of data */
         ztest_unit_test_setup_teardown(test_txt_export, setup, teardown),
+        /* Text mode: update notification */
+        ztest_unit_test_setup_teardown(test_txt_update_callback, setup, teardown),
 
         /* Bin mode: GET request */
         ztest_unit_test_setup_teardown(test_bin_get_meas_ids_values, setup, teardown),
@@ -98,7 +100,9 @@ void test_main(void)
 #endif
         /* Bin mode: exporting/importing of data */
         ztest_unit_test_setup_teardown(test_bin_export, setup, teardown),
-        ztest_unit_test_setup_teardown(test_bin_import, setup, teardown)
+        ztest_unit_test_setup_teardown(test_bin_import, setup, teardown),
+        /* Bin mode: update notification */
+        ztest_unit_test_setup_teardown(test_bin_update_callback, setup, teardown)
     );
 
     ztest_run_test_suite(thingset_tests);