A lid that is a container
On this page11
A product on a shelf appears with a role, and the role is recorded on the membership
Not on the product. Which means the same product can appear as a container in one group and as a closure in another, and seven products across the catalog do exactly that.
All seven have a component kind of closure
A cap for a roller ball bottle, a lip balm tube cap, a deodorant lid, a round tub lid, two round pail lids and a square pail lid. Every one of them is a lid by classification.
And one of the seven is on this shelf
So this group includes a product whose classification says closure and whose role here may be either, depending on which membership row is read.
Which is not an error, and the reason is physical
A shallow round pail lid is a tray. Anybody sorting beads or sequins on a bench has used a lid as a dish, and the routing layer records that use.
So component kind and role can disagree and the disagreement carries information
Component kind says what the product is in the supplier catalog. Role says what it is doing in a particular use case. Collapsing the two would lose the second.
It does mean a count has to be careful about which field it uses
Counting products by component kind gives one answer. Counting shelf rows by role gives another. On a shelf with a dual role row the two differ by one.
Seven rows out of 2,150 is a small effect and a precise one
Which is the useful kind of finding: it changes nothing for most purposes and it tells anybody building a count exactly where the discrepancy comes from.
And it is the third schema observation on this shelf
Three buying flags that are not independent, a third product class that is almost unrouted, and a role field that belongs to the membership rather than to the product.
All three were found by enumerating a field rather than filtering one
Which is the method this library keeps arriving at. The trains and dioramas property found a contradictory family name the same way, and the personal small items property found five urea closures.
The shelf itself is the shared one plus three rows
253 containers and 289 closures against the 251 and 288 that nine groups share identically. The knit and crochet property describes the three extra rows and the sewing notions property enumerates the rest.