Nested Classifications

Overview of the Nested Classifications labeling tool in Ango Hub

Ango Hub allows annotators to answer multiple, nested questions regarding individual labels, relations, or top-level classifications.

In the example above, we ask annotators to draw a polygon. Then, they answer questions related to the polygon they’ve just drawn. Each question’s answer determines which question will be asked next.

Here, if annotators select the “clothing” answer, they will be shown a question asking what type of clothing it is. If then they select “shirt” they will be asked the shirt’s gender, and so on.

You may nest classifications under existing classifications conditionally (i.e. to appear once a user selected a specific answer) or unconditionally (the nested classification appears regardless of what answer the user picks.)

Setting Up Nested Classifications on Ango Hub

From the project’s Settings tab, enter the Category Schema section.

Click on the label or relation on which you’d like to ask nested questions. In our example, we expand a “Vehicle” bounding box.

Click on the Add Classification button towards the bottom.

If you are adding a nested classification to a tool or relation class, you will be prompted to select the type of classification you need.

If you are adding a nested classification to another classification, you will be prompted to select the classification answer that should be selected by the user for the nested classification to trigger. (More on classification in Ango Hub.)

If you are nesting a classification under an existing classification, and if you wish for the nested classification to appear regardless of the answer picked by the user, pick the Any option from the dropdown:

If you are adding a classification to a Text-type classification tool, the nested classification will be displayed regardless of the text being input as soon as the user starts entering text.

The Add Classification button will not appear for classifications if no options have been added.

A new labeling tool will appear. Fill up its title and description as before, and add options if available.

From here, if you click on Add Classification again, you can nest a further question. For example, we can show annotators a free text tool if they answer “Other.”

Enable the Required toggle on a nested classification if labelers must answer it before submitting the task. Required conditional classifications are enforced only when their parent answer makes them visible.

How to Answer Nested Questions

In the labeling editor, right-click on the annotation where you’d like to answer the nested questions. You can also expand an annotation or relation in the Objects panel and answer its questions there.

A contextual menu will appear. Clicking on it will expand the questions if available.

Relation questions are available wherever relations are supported, except in 3D MSFT projects and the DICOM series editor. When a required relation question is unanswered or an answer does not match its configured format, Ango Hub blocks submission and identifies the relation that needs attention.