Hierarchical tagging

ThreeTags uses a hierarchical tagging system that allows users to arrange notes and bookmarks in many ways suitable for their purposes. Hierarchical tagging system is a combination of the conventional hierarchical system (folders/directories) and the “flat” tagging system (categories) employed by many web-based services.

Hierarchical system (directories)

In the hierarchical system files are kept organized by storing related files in the same directory (or folder). Together, the directories form a hierarchy, or tree structure. A typical file system may contain thousands of directories.

Virtual folders remind us the physical folders one can use to organize the papers or a bookshelf in a library. It stems of physical characteristics of objects. If you have a book, you can put it in only one place, and then to find it again, you have to describe which shelf it is on in no uncertain terms. It is organized into non-overlapping categories that get more detailed at lower and lower levels, and any concept is supposed to fit in one and only one category. This scheme is a response to physical constraints on storage, and hierarchy is a good way to manage physical objects.

However, this system has several important weaknesses. First of all, items do not always fit exactly inside one and only one category, so populating the hierarchy becomes problematic. Secondly, hierarchies are inflexible, and require a certain prediction of their future use. Last but not least, large hierarchies, even if well-thought-out, are often difficult to navigate if some items do not obviously fall into one and only one category.

Tagging (categories)

The tagging system has been introduced to overcome these weaknesses, and it is successfully used by many Web 2.0 applications.

What is a tag? A tag is a non-hierarchical keyword assigned to any item of information. A tag describes this item and helps to locate in later on. Users choose tags informally, basically adding everything that would help them describe an item. This flexibility allows people to classify their collections of items in the way that they find useful.

People often find it hard to be consistent at organizing things, and tagging allows it not to be a disadvantage, where inconsistency in folder-based categorization often result in difficulties finding items needed. Tagging allows users to put one item in multiple categories, and items with multiple tags assigned to them are usually easier to find.

However, large collections of tagged items often grow “messy”. The more tags a user has, the more the user needs to organize the tags themselves – a “flat” list of several hundred tags can be unwieldy and difficult to search through.

Hierarchical Tagging

Hierarchical tagging solves this problem by allowing users to organize tags themselves in simple hierarchies.

Examples below illustrate the benefits and typical uses of hierarchical tags. As is the convention at www.threetags.com, tags are separated by semicolons; sub-tags are separated from parent tags by colons.

1. Shopping list

A list of shopping items might have the following taxonomy (a system of categories):

• Shopping: groceries: vegetables
• Shopping: groceries: meat
• Shopping: groceries: drinks
• Shopping: toys
• Shopping: patio furniture

In this example hierarchical tags are used as simple folders, as most shopping items can be easily assigned to a single category. Note that a “flat” tagging system would be not as convenient in this case.

2. Contact list

A list of personal contacts can be organized as this:

• People: family
• People: friend
• People: friend: Toronto
• People: friend: Vancouver
• People: school classmate
• People: college classmate
• People: colleague

This example illustrates the flexibility of the hierarchical tagging system: as a college classmate can be a colleague and a friend, a purely hierarchical taxonomy would, first of all, force the user to make an unnecessary choice as to whether to classify the person as a classmate, a colleague, or a friend; secondly, users cannot see all their friends in a list together, as in the purely hierarchical system a “Friend/Vancouver” item would not show in the parent “Friend” folder/category.