Talk:Q16887380

set (Q36161)

set (Q36161) is mathematical object (Q246672), but group (Q16887380) is its non-mathematical analogue --Fractaler (talk) 11:35, 25 September 2017 (UTC)

More precise definition

See the larger discussion here. In response to a recent question in the project chat, I gave the following definition of "group."

To reverse engineer a definition for group (Q16887380), I translated all the descriptions to English. A summary of common descriptions are "entities with similar characteristics," "set of things or people," "group of living things," "two or more objects," or "entities with similar characteristics and coexistence." (My favorite Google translation, however, is: "what is and what is what is" 😂) My assesment, then, is that a "group" is an exaustive collection of two or more concurrent physical things (real or fictional) that have an mutual association or defining charactersitic. So examples of groups are: The Beatles (Q1299), the stars in our galaxy, and Bonnie and Clyde (Q219937). Examples that are not groups are John Lennon (only one item), the set {John Lennon and Paul McCartney} (not exhaustive), the set of real numbers (not physical), presidents of the United States (not concurrent), and the set { New York City (Q60) and Julius Caesar (Q1048) } (no association). So every group is a class (Q16889133), but not every class (Q16889133) is a group.

Does anybody object to this definition? If not, I will change the description to "collection of two or more concurrent people or physical items." (I trimmed down my definition a bit from what I said in the project chat because it is too long for a description). ~ The Erinaceous One 🦔 06:36, 19 September 2020 (UTC)

@The-erinaceous-one: I would object almost to all points of the definition of the group. 1) exhaustive? I think any subgroup is a group too. Note that {John Lennon and Paul McCartney} is a duet so it's a group. 2) two or more? There are set of 0 (Q39604693) and monad (Q39604065) items. 3) concurrent? probably I agree. 4) physical? no. There can be a group of digits, e.g. 5) association? probably yes, but this is not scientific thing. I would change to followint: "closed collection of (concurrent) entities having mutual association or defining characteristic". --Infovarius (talk) 15:14, 22 September 2020 (UTC)

@Infovarius: 1) I will yield that a group does not be exhaustive, in theory, but such a group would be arbitrary---and therefore not notable---so there is no reason to make such as group in Wikidata. We wouldn't want, for instance, an item that is "every state in the USA, except Kansas." 2) The "two or more" or more criteria was based on the descriptions. A "group with one member" also conflicts with the English meaning of "group," though that might differ for other languages. 4) A "group of digits" is a mathematical object so it would be better modeled as a mathematical set. But the are some nonphysical things that make sense as a "group," namely non-physical works of art, such as a group of stories or musical compositions. There could also be a group of events. But do we want to have a "group of integers" or other mathematical objects? If we do, then what's the difference between a group and a mathematical set? 5) Yes, I think it is okay for the definition to be fuzzy for some groups. For example, some groups are clusters--such as a group of islands--and the inclusion or exclusion of particular outlying items might vary between sources.

In your definition, what do you mean by "closed"? — The Erinaceous One 🦔 07:47, 23 September 2020 (UTC)

Hard to think at 3a.m. and I should admit that it is probably the same as "exhaustive"... --Infovarius (talk) 22:21, 24 September 2020 (UTC)

@Infovarius: On the other discussion page, we have proposed changes to Q16887380. Could we get your buy-in? User:The-erinaceous-one/types of collections#Wrap up: Phase 2. — The Erinaceous One 🦔 06:58, 27 October 2020 (UTC)

Proposed Change

Due to continuing discussion, our proposal has changed a bit. In order to refine the definition of Q16887380, we propose dividing it among three classes:

• set (Q28813620): A well-defined collection of entities. Analogous to a mathematical set.
• group (Q16887380): A well-defined collection of discrete entities who choose or are assigned to be part of a collective whole. Examples include people in a musical band, nations in the United Nations, buildings in a campus, and mice assigned to an experimental group. A geographic region is not a group (Q16887380) because it is a continuous, rather than discrete, set of points. The planets in our solar system are not a group because nobody assigned them as such. A group can have zero, one, or more members.
• cluster (Q21157127): A fuzzily-defined collection of multiple discrete entities that are clustered together, either physically or conceptually. Examples include a tornado outbreak (Q2696963) or group of works (Q17489659).

These three classes would have the following class hierarchy:

• collective entity (Q99527517)
  • set (Q28813620)
    • group (Q16887380)
  • cluster (Q21157127)

See the full discussion here. — The Erinaceous One 🦔 11:15, 1 November 2020 (UTC)