Phylogeny

When the phylogeny is included in relationships among items, terms are defined as follows.

Metaphorical words like "parent," "child," "ancestor," and "descendant" are often used to show the relationship between the items. This parent-child relationship is decided when the item is uploaded.

Definition

1. The items that have constituent items are called "original/root item" and shown as $I^◯$.

2. The items that does not have constituent items are called "derivative/non-root item" and shown as $I^-$.

3. Among the items that share the same constituent, the ones that are uploaded earlier are called "parent items" and the ones uploaded later are called "child items."

4. Among the items that share the same root, the ones that are uploaded earlier are called "ancestral items" and the ones uploaded later are called "descendant items."

5. For a certain item $I$, the child item is shown as$I^{-1}$ and the parent item as$I^{1}$.