Google Mail (GMail) offers the feature to nest a new label (Google-Gmail-speak for "tag") under another one. You get there following this path:
Gmail > Mail settings > Labels > "Create new label" > "Nest Label under:"
With this feature, you can define a label "sports" and nest another label "volleyball" under it. Then you get "sports" and "sports/volleyball" respectively.
Unfortunately Google has mixed two different concepts which results in bad usability: wrong behavior expectance.
When you are thinking of the concept of labels or tags, you probably get the following idea: whenever I label anything with "sports/volleyball", I expect to see those items (emails) also in "sports" since "volleyball" is a refinement of "sports".
When you are prefer to think of folders, you will get the expectance to find things stored in "sports/volleyball" only there.
Consider following situation:
labeled with "sports": "My sports plan.txt"\\ labaled with "sports/volleyball": "Beachvolleyball schedule.txt"\\
This is, what you see in Gmail interface with current implementation:
contained in "sports": "My sports plan.txt"\\ contained in "sports/volleyball": "Beachvolleyball schedule.txt"\\
This is, what you might expect from a label point of view:
contained in "sports": "My sports plan.txt" and "Beachvolleyball schedule.txt"\\ contained in "sports/volleyball": "Beachvolleyball schedule.txt"\\
Google tried to combine both worlds as they stated in a very interesting whitepaper. They designed the web interface of Gmail to satisfy people from the "folder-world" and people from the "label-world". This works pretty good so far. Until they start to break the metapher for the "label-world-people" by introducing hierarchical structures.
The logical concept of hierarchies with folders differs from the logical concept of hierarchies withing labels. Different folders always mean different contents. But labels that are super-labels of other labels mean the combined set of items labeled with all sub-labels and the super-label.
Another example of how hierarchical structures conflict with modern information handling.
Note: this blog entry was originally authored using Serendipity and converted to Org-mode format for publicvoit via a dumb script. This may result in bad format or even lost content. Please write a comment if you want to get in touch with me so that I can try to fix things.