diff --git a/src/modb_types.c b/src/modb_types.c
index afc175a..b7758b7 100644
--- a/src/modb_types.c
+++ b/src/modb_types.c
@@ -138,4 +138,178 @@ void freeGroups(struct group_t ***groups_ptr, size_t n_groups)
   free(groups);
   *groups_ptr = 0;
 }
+
+
+struct metadata_t *allocMetadata(void)
+{
+  struct metadata_t *metadata;
+
+  metadata = malloc(sizeof(struct metadata_t));
+  if (metadata == 0) {
+    fprintf(stderr, "[%d]malloc: (%d) %s\n", __LINE__, errno, strerror(errno));
+  }
+  memset(metadata, 0, sizeof(struct metadata_t));
+
+  return metadata;
+}
+struct metadata_t **allocMetadataList(size_t n_metadatas)
+{
+  struct metadata_t **metadatas;
+
+  metadatas = (struct metadata_t **)malloc(sizeof(struct metadata_t *) * n_metadatas);
+  if (metadatas == 0) {
+    fprintf(stderr, "[%d]malloc: (%d) %s\n", __LINE__, errno, strerror(errno));
+    return 0;
+  }
+  memset(metadatas, 0, sizeof(struct metadata_t *) * n_metadatas);
+
+  return metadatas;
+}
+void freeMetadata(struct metadata_t **metadata_ptr)
+{
+  struct metadata_t *metadata = *metadata_ptr;
+
+  if (metadata->ext != 0) {
+    freeMetadataExt(&metadata->ext);
+  }
+
+  if (metadata->object != 0) {
+    freeObject(&metadata->object);
+  }
+
+  if (metadata->n_groups > 0) {
+    if (metadata->group_ids != 0) {
+      free(metadata->group_ids);
+      metadata->group_ids = 0;
+    }
+    if (metadata->groups != 0) {
+      freeGroups(&metadata->groups, metadata->n_groups);
+    }
+    metadata->n_groups = 0;
+  }
+
+  if (metadata->owner != 0) {
+    freeUser(&metadata->owner);
+  }
+
+  if (metadata->title != 0) {
+    free(metadata->title);
+    metadata->title = 0;
+  }
+
+  free(metadata);
+  *metadata_ptr = 0;
+}
+void freeMetadataList(struct metadata_t ***metadata_list_ptr, size_t n_metadatas)
+{
+  size_t idx;
+  struct metadata_t **metadatas_list= *metadata_list_ptr;
+
+  for (idx = 0; idx < n_metadatas; idx++) {
+    if (*(metadatas_list + idx) != 0) {
+      freeMetadata((metadatas_list + idx));
+    }
+  }
+
+  free(metadatas_list);
+  *metadata_list_ptr = 0;
+}
+
+struct object_t *allocObject(void)
+{
+  struct object_t *object;
+
+  object = malloc(sizeof(struct object_t));
+  if (object == 0) {
+    fprintf(stderr, "[%d]malloc: (%d) %s\n", __LINE__, errno, strerror(errno));
+  }
+  memset(object, 0, sizeof(struct object_t));
+
+  return object;
+}
+struct object_t **allocObjects(size_t n_objects)
+{
+  struct object_t **objects;
+
+  objects = (struct object_t **)malloc(sizeof(struct object_t *) * n_objects);
+  if (objects == 0) {
+    fprintf(stderr, "[%d]malloc: (%d) %s\n", __LINE__, errno, strerror(errno));
+    return 0;
+  }
+  memset(objects, 0, sizeof(struct object_t *) * n_objects);
+
+  return objects;
+}
+void freeObject(struct object_t **object_ptr)
+{
+  struct object_t *object = *object_ptr;
+
+  if (object->data != 0) {
+    free(object->data);
+    object->data = 0;
+  }
+
+  free(object);
+  *object_ptr = 0;
+}
+void freeObjects(struct object_t ***objects_ptr, size_t n_objects)
+{
+  size_t idx;
+  struct object_t **objects = *objects_ptr;
+
+  for (idx = 0; idx < n_objects; idx++) {
+    if (*(objects + idx) != 0) {
+      freeObject(objects + idx);
+    }
+  }
+
+  free(objects);
+  *objects_ptr = 0;
+}
+
+struct metadata_ext_t *allocMetadataExt(void)
+{
+  struct metadata_ext_t *metadata_ext;
+
+  metadata_ext = malloc(sizeof(struct metadata_ext_t));
+  if (metadata_ext == 0) {
+    fprintf(stderr, "[%d]malloc: (%d) %s\n", __LINE__, errno, strerror(errno));
+  }
+  memset(metadata_ext, 0, sizeof(struct metadata_ext_t));
+
+  return metadata_ext;
+}
+struct metadata_ext_t **allocMetadataExts(size_t n_metadata_exts)
+{
+  struct metadata_ext_t **metadata_exts;
+
+  metadata_exts = (struct metadata_ext_t **)malloc(sizeof(struct metadata_ext_t *) * n_metadata_exts);
+  if (metadata_exts == 0) {
+    fprintf(stderr, "[%d]malloc: (%d) %s\n", __LINE__, errno, strerror(errno));
+    return 0;
+  }
+  memset(metadata_exts, 0, sizeof(struct metadata_ext_t *) * n_metadata_exts);
+
+  return metadata_exts;
+}
+void freeMetadataExt(struct metadata_ext_t **metadata_ext_ptr)
+{
+  struct metadata_ext_t *metadata_ext = *metadata_ext_ptr;
+
+  free(metadata_ext);
+  *metadata_ext_ptr = 0;
+}
+void freeMetadataExts(struct metadata_ext_t ***metadata_exts_ptr, size_t n_metadata_exts)
+{
+  size_t idx;
+  struct metadata_ext_t **metadata_exts = *metadata_exts_ptr;
+
+  for (idx = 0; idx < n_metadata_exts; idx++) {
+    if (*(metadata_exts + idx) != 0) {
+      freeMetadataExt(metadata_exts + idx);
+    }
+  }
+
+  free(metadata_exts);
+  *metadata_exts_ptr = 0;
 }
diff --git a/src/modb_types.h b/src/modb_types.h
index e9214b2..5eb4dc4 100644
--- a/src/modb_types.h
+++ b/src/modb_types.h
@@ -43,16 +43,95 @@ struct group_t {
   size_t n_members;
 };
 
+struct metadata_t {
+  unsigned int id;
+
+  char *type;
+  size_t type_len;
+
+  char *title;
+  size_t title_len;
+
+  unsigned int owner_id;
+  struct user_t *owner;
+
+  int64_t created_on;
+  int64_t updated_on;
+  int64_t deleted_on;
+
+  unsigned int *group_ids;
+  struct group_t **groups;
+  size_t n_groups;
+
+  struct object_t *object;
+  struct metadata_ext_t *ext;
+};
+
+struct object_t {
+  unsigned int id;
+
+  char *data;
+  size_t data_len;
+};
+
+struct metadata_ext_t {
+  unsigned int id;
+
+// TODO: dynamic extended metadata definition
+//  struct metadata_ext_value_t **meta_ext;
+//  size_t n_meta_ext;
+};
+
+//struct metadata_ext_value_t {
+//  char *key;
+//  enum e_column_type_t type;
+//  union {
+//    void *vptr;_ptr
+
+//    int8_t int8;
+//    uint8_t uint8;
+
+//    int16_t int16;
+//    uint16_t uint16;
+
+//    int32_t int32;
+//    uint32_t uint32;
+
+//    int64_t int64;
+//    uint64_t uint64;
+
+//    float flt;
+//    double dbl;
+
+//    char *ptr_str;
+//  } value;
+//  size_t value_len;
+//};
 
 struct user_t *allocUser(void);
 struct user_t **allocUsers(size_t n_users);
 void freeUser(struct user_t **user);
-void freeUsers(struct user_t **users, size_t n_users);
+void freeUsers(struct user_t ***users_ptr, size_t n_users);
 
 struct group_t *allocGroup(void);
 struct group_t **allocGroups(size_t n_groups);
 void freeGroup(struct group_t **group);
-void freeGroups(struct group_t **groups, size_t n_groups);
+void freeGroups(struct group_t ***groups_ptr, size_t n_groups);
+
+struct metadata_t *allocMetadata(void);
+struct metadata_t **allocMetadataList(size_t n_metadatas);
+void freeMetadata(struct metadata_t **metadata);
+void freeMetadataList(struct metadata_t ***metadata_list_ptr, size_t n_metadatas);
+
+struct object_t *allocObject(void);
+struct object_t **allocObjects(size_t n_objects);
+void freeObject(struct object_t **object);
+void freeObjects(struct object_t ***objects_ptr, size_t n_objects);
+
+struct metadata_ext_t *allocMetadataExt(void);
+struct metadata_ext_t **allocMetadataExts(size_t n_metadata_exts);
+void freeMetadataExt(struct metadata_ext_t **metadata_ext);
+void freeMetadataExts(struct metadata_ext_t ***metadata_exts_ptr, size_t n_metadata_exts);
 
 
 #endif // H__MODB_TYPES__