# Arbital "parent" relationship

Most pages in Ar­bital can be con­nected. We call these con­nec­tions re­la­tion­ships. Par­ent-child re­la­tion­ship is one of the mul­ti­ple re­la­tion­ship types and is the tight­est way to con­nect pages on Ar­bital. This re­la­tion­ship is used to in­di­cate that the child is a crit­i­cal com­po­nent of the par­ent, or that the par­ent is the sum of its chil­dren. For ex­am­ple, the SI units par­ent page will have kilo­gram, sec­ond, me­ter, etc… as chil­dren pages.

It’s perfectly fine for a page not to have any par­ents or chil­dren. It can still be found by search­ing, and can be used as a tag, req­ui­site, or link.

### When to cre­ate a par­ent-child relationship

When the child doesn’t make sense out­side of the con­text of the par­ent. For ex­am­ple:

• Chap­ter 2 of “Harry Pot­ter and The Sorcerer’s Stone” doesn’t make a lot of sense by it­self. So it’s a child of “Harry Pot­ter and The Sorcerer’s Stone (book)” page, which is it­self a child of “Harry Pot­ter (book se­ries)” page.

When there is some well-known, es­tab­lished hi­er­ar­chy. For ex­am­ple:

• “C. lu­pus (species)”, or com­monly known as gray wolf, is a child of the “Ca­nis (genus)” page, which is a child of “Canidae (fam­ily)” page, etc… This tax­on­omy of biolog­i­cal or­ganisms is pretty well es­tab­lished.

When the par­ent is defined as the sum of some parts. For ex­am­ple:

• Arith­metic is ad­di­tion, sub­trac­tion, mul­ti­pli­ca­tion and di­vi­sion by defi­ni­tion. So “Arith­metic” page will have those pages as chil­dren.

More gen­er­ally the par­ent-child re­la­tion­ship sug­gest a “is-a” or a “is-a-part-of” con­netion. Some­times it’s also sim­ply used for or­ga­niz­ing pages in a hi­er­ar­chy to make it eas­ier to find them.

### When not to cre­ate a par­ent-child relationships

Just be­cause two con­cepts are of­ten as­so­ci­ated. For ex­am­ple:

• Chloro­phyll, an im­por­tant bio­molecule used for pho­to­syn­the­sis, is usu­ally as­so­ci­ated with plants. But not all plants have chloro­phyll, and chloro­phyll can oc­cur out­side of plants, e.g. in al­gae.

Just be­cause two con­cepts are closely re­lated. For ex­am­ple:

• Plants, chloro­phyll, and pho­to­syn­the­sis are pretty closely re­lated. But pho­to­syn­the­sis as a pro­cess can hap­pen in things other than plants or us­ing a mechanism that doesn’t in­volve chloro­phyll. And some plants don’t even have chloro­phyll.

Some­times it can be un­clear if the pages should have a par­ent-child re­la­tion­ship. If you run into a case you can’t clearly re­solve, please post it here, so we can dis­cuss it, learn from it, and re­fine these defi­ni­tions.

Parents:

• This gives a few clear ex­am­ples, but does not help much with slightly less clear judge­ments (e.g. should Nick Bostrom be a child of Peo­ple or just tagged with it?). Clas­sifi­ca­tion sys­tems are tricky and of­ten sub­jec­tive, prob­a­bly worth tak­ing a close look at Wik­i­data and other similar pro­jects for in­spira­tion when we want to work out de­tailed guidelines for this.

• Child, be­cause “Nick Bostrom is a per­son” and “Nick is a part of the ‘peo­ple’ ob­ject” and with­out “Nick Bostrom” the ob­ject “peo­ple” is not com­plete.

You’d add the tag “Peo­ple” if the page talks about that con­cept, eg a page about peo­ple of New York.

• If ap­plied to all “is a” state­ments, some pages are go­ing to have a lot of par­ents even­tu­ally. This is prob­a­bly fine, but worth com­ing back to and re­con­sid­er­ing once we’ve seen the sys­tem in wide­spread use imo.