With so many systems, items are grouped into hierarchies. This is used especially with computer systems. It is argued that this is the way the things are organised, but this is mistaken.
Consider your Web browsing. You might want to save a link as a bookmark (also called a favourite). Many browsers allow you to put the bookmark in a category. The hierarchy is all bookmarks – category – bookmarks in that category.
Similarly, how do you categorise your E-mail?
This is less than totally useful. It works for many cases, but it fails when you have items that fit in more than one category.
Sets make much more sense.
I like humour, and I have a category for humour. I like business articles, too. Why can I not specify that the bookmark is in both humour and business?
I also like good articles about programming. These might be connected with business; why can I not specify that the bookmark is in both business and programming? The article might be humorous, too, and why can I not have it in all three categories?
For the three categories, there are seven combinations. Do I have to create all seven? If I then wanted to find all business articles, I would have to look at four bookmark categories (business, business-programming, business-humour, business-programming-humour).
This might not be the end of it. If I want a category of courses one can take, there would be fifteen possible combinations, and all could happen.
The next number is 31.
I would like to be able to specify that my bookmark is to go into more than one category. It would be easy enough to put it in just one category for those who do not care about this issue.
How about it browser and E-mail programmers?