# Identifying Objects

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In the `MetaData` component, objects in ILIAS are generally identified by
three parameters:

1. **obj_id:** The `obj_id` of the object if it is a repository object, else the
   `obj_id` of its parent repository object. If the object does not have
   a fixed parent  (e.g. MediaObject), then this parameter is 0.
2. **sub_id:** The `obj_id` of the object. If the object is a repository object by
   itself and not a sub-object, then you can set this parameter to 0, but
   we recommend passing the `obj_id` again.
3. **type:** The type of the object (and not its parent's), e.g. `'crs'` or `'lm'`.

For example, consider three different objects:

- a Group with `obj_id` 123,
- a Page with `obj_id` 54 in an ILIAS Learning Module with `obj_id` 456,
- and a MediaObject with `obj_id` 789.

The corresponding ID-triples would then be

|             | **obj_id** | **sub_id** | **type**
|-------------|------------|------------|----------
| Group       | 123        | 123        | grp
| Page in LM  | 456        | 54         | pg
| MediaObject | 0          | 789        | mob