Like many other Web 2.0 systems, Piggydb supports tagging to classify knowledge fragments.
While tagging is simply for classifying a piece of information and allowing it to be found again by browsing or searching, in the context of folksonomy, its simplicity (non-hierarchical keywords) enables organizing information by many people collaboratively, known as “collective intelligence”, and connecting like-minded people.
Piggydb is not a social networking application, so it concentrates on the classifying nature of tagging. In terms of classifying, tagging has many advantages over existing systems such as directories/folders and categories. Tagging is generally more flexible and less brain-racking, and is used to resolve the “Bat problem”.
The ‘Bat problem’ was coined by Japanese economist Yukio Noguchi to describe a problem which arises when classifying information and goods. Material things and information can have multiple attributes that are used descriptively depending on the context (Bats have the properties of both birds and beasts – http://mythfolklore.net/aesopica/milowinter/43.htm).
However, tagging also has its own problems. One of them is losing the grasp of the entire set of tags when the number of tags is growing. Piggydb offers hierarchical tagging to tackle this problem.
Hierarchical tagging allows you to classify a tag through other tags, exactly like knowledge fragments, and the classification is transitive; that is, if there is a tag “cat” classified with a tag “animal” and you classify some fragments with “cat”, then those fragment will be classified as an “animal” also. The hierarchical tagging feature allows you to classify fragments more naturally, and drill down a large number of fragments more easily and smoothly.