The Cargo extension (https://www.mediawiki.org/wiki/Extension:Cargo) lets you declare a certain field as having "allowed values" (like "Blue, Red, Yellow"), but it doesn't allow for defining a field as holding a hierarchy of values. An example would be a field called "Topic", which can hold both major topics and minor sub-topics as values.
As I see it, the steps of such a project may look something like:
* Add support for declaring hierarchy fields
* Add support for querying hierarchy fields, using a new Cargo keyword, "WITHIN" (as in "where=City WITHIN 'Asia'"). This would need to work with both single-value fields and fields that hold multiple values.
* Add support for such fields within Cargo's Special:Drilldown interface - a line there might look like:
Fruits (23) * Vegetables (30) ("Vegetables" only (3) * Root vegetables (15) ("Root vegetables" only (1) * Carrots (12) * Turnips (2) ) * Peppers (12) )
* Add support for hierarchy fields in the Page Forms extension - so that such fields automatically get the right input type ("tree"), with the right values filled in
* Also make hierarchy fields easy to create in Page Forms' helper pages, like Special:CreateTemplate and Special:CreateClass
=Internship project details=
* Primary mentor: Nischay Nahata (@Nischayn22)
* Co-mentor: Yaron Koren (@Yaron_Koren), Tobias Oetterer (@Oetterer)
* Skills: PHP, SQL
* Estimated project time for a senior contributor: 2 weeks
** T29702 (may no longer be valid - this should be checked)
** T72704 (also may no longer be valid)