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Originally Posted by Huisie
My method seemed easier - I was merely manipulating info that was already there rather than having to create it.
I couldn't create a custom column from that list, though.
Does this matter, as long as I am able to sort by "Genre", one way or another?
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What matters is that what you do works for you.
Quote:
General confusion:
To this novice, it appears custom columns can also be user categories and/or groups.
I can't understand the difference between columns, user categories and groups.
I know you gave an explanation (quoted below) but I can't get my head around it:
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I am probably diving into the deep end, but here goes...
We are dealing with two basic concepts, 'thing' and the 'idea of thing'. For example, consider a stone. The stone exists, you can throw it, etc. It is a 'thing' or (what I like better) an 'instance'. Now consider telling a friend over the phone that you have the stone. Your friend is left with an 'idea of stone', not an 'instance of stone'. Suppose your friend gets interested and calls other friends to find out what stones they have. Your friend's 'idea of stone' now encompasses many instances of stone. In other words, for your friend, 'stone' is a category, not an instance. A third party might note that 'stone' has two very different meanings. It is ambiguous; its meaning depends on context.
Now assume that your friend gets a stone. Suddenly your friend must deal with 'instance' and 'idea' at the same time, and must work out a system for knowing which meaning applies, when. We have the same problem in calibre. A term can describe an instance, a category, or both . The questions then become "How do we disambiguate between the meanings?" and "How do we manipulate the meanings?" To do this in a computer program like calibre, we must have a way of concretely representing (modeling) the various meanings of information.
In calibre, we can say that a column (any column) is a category, representing the 'idea of something'. A row is a book, an instance of something. The cell (row/column) is therefore an instance of a category. For example, the Authors column contains names of authors (instances at an abstract level). The Titles column contains instances of titles. If you create a custom column, then one hopes that the column contains instances consistently fitting a category (idea).
The difficulty that arises is that an instance might fit into more than one category. For example, an author can be categorized by nationality, location, style, gender, genre, hair color, and a host of other notions, none of which are conveyed by the idea 'Author'. Tags are even worse, because the notion of tag is much more abstract than author. Calibre deals with this difficulty by providing 'user categories'. When you create a user category, you are working with the 'idea' of something. What you put into the category are the instances that somehow are connected to that idea. You might create a category called Spanish Authors, an 'idea' that would provide more information about authors. You might create a category called 'Bad Things', another idea which could contain instances of almost any kind (tag, author, publisher, etc).
Bottom line: categories represent an 'idea' about and are independent of a book. Categories can exist even if the library is empty. Columns are categories. Book metadata is a row of tags, authors, etc representing 'instances' of category defined by the columns. User categories are similar to columns in that they convey additional 'ideas' about instances.
Regarding hierarchical items: it could be argued that they are both a category and an instance. However, for convenience we must pick one definition. In calibre, a hierarchical item exists only if it appears on a book, so it is an instance, not a category.