We humans are categorizing machines, which is to say, we like to create metaphorical buckets, and put things inside. But there are different kinds of buckets, and different ways to model them in OWL and gist. The most common bucket represents a kind of thing, such as Person, or Building. Things that go into those buckets are individuals of those kinds, e.g. Albert Einstein, or the particular office building you work in. We represent this kind of bucket as an owl:Class and we use rdf:type to put something into the bucket.
Another kind of bucket is when you have a group of things, like a jury or a deck of cards that are functionally connected in some way. Those related things go into the bucket (12 members of a jury, or 52 cards). We have a special class in gist called Collection, for this kind of bucket. A specific bucket of this sort will be an instance of a subclass of
OJs_Jury is an instance of the class
Jury, a subclass of
gist:Collection. We use
gist:memberOf to put things into the bucket. Convince yourself that these buckets do not represent a kind of thing. A jury is a kind of thing, a particular jury is not. We would use
rdf:type to connect OJ’s jury to the
Jury, and use
gist:memberOf to connect the specific jurors to OJ’s jury.
A third kind of bucket is a tag which represents a topic and is used to categorize individual items for the purpose of indexing a body of content. For example, the tag “Winter” might be used to index photographs, books and/or YouTube videos. Any content item that depicts or relates to winter in some way should be categorized using this tag. In gist, we represent this in a way that is structurally the same as how we represent buckets that are collections of functionally connected items. The differences are 1) the bucket is an instance of a subclass of
gist:Category, rather than of
gist:Collection and 2) we put things into the bucket using
gist:categorizedBy rather than
gist:memberOf . The Winter tag is essentially a bucket containing all the things that have been indexed or categorized using that tag.
Below is a summary table showing these different kinds of buckets, and how we represent them in OWL and gist.
|Kind of Bucket||Example||Representing the Bucket||Putting something in the Bucket|
|Individual of a Kind||John Doe is a Person||Instance of owl:Class||rdf:type|
|A bucket with functionally connected things inside||Sheila Woods is a member of OJ’s Jury||Instance of a subclass of gist:Collection||gist:memberOf|
|An index term for categorizing content||The book “Winter of our Discontent” has Winter as one of its tags||Instance of a subclass of gist:Category||gist:categorizedBy|