Raising Awareness

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An Introduction to Tags and Tagging

What is a Tag?

Wikipedia defines a tag as "a non-hierarchical keyword or term assigned to a piece of information (such as an internet bookmark, digital image, or computer file)" [1]. Tags, which are a form of metadata, allow resources to be more easier found.


In the pre-Internet era, library catalogues used keywords to help users find titles on specific topics. Later, publishers of early Web sites started to use keywords to help people to find content. Then around 2003, tagging was developed by the social bookmarking site Delicious, and subsequently used by other social software services such as Flickr, YouTube and Technorati.

Tag Features

A list of typical characteristics of tags is given below:

  • Tags are chosen by the creator and/or by the viewer of the tagged item.
  • Tags are not part of a formal subject indexing term set.
  • Tags are informal and personal.
  • An item may have multiple tags assigned to it.
  • There is no 'wrong' tag.

Tag Clouds

Web sites that use tags often display the tags visually as a tag cloud. These usually take the form of an alphabetical list of tags and use font size and/or colour to identify the most frequently used tags. This enables viewers to either pick from the alphabetical list or to easily spot the most popular tags.

Tag Cloud Types

A number of different types of tag clouds may be found. For example:

  • The size represents the number of times that tag has been applied to a single item.
  • The size represents the number of items to which a specific tag has been applied.
  • The size represents the number of items in a content category.


In situations where many users add tags to lots of items, a collection of tags is built up over time. Such a collection tags may be referred to as a folksonomy. A more formal definition of folksonomy is a set of keywords that is built up collaboratively without a pre-determined hierarchical structure.

Users of tagging systems can see the tags already applied by other people and will often, therefore, choose to use existing tags. However, they will create new tags if no existing tag is suitable or if the existing ones are not specific enough.

Hash Tags (# Tags)

Hash tags (also written as 'hashtags') are used in messages using services such as Twitter. The hash symbol (#) is placed before the word to be treated as a tag, as in the example below.

#goji berries are the new #superfood

This enables tweets on a specific topic to be found by searching on the hash tag.

Adding Tags

Systems vary in how you enter tags. When a single text box is provided and you want to enter more than one tag, you will need to use a separator between the tags. The most popular separator is the space character but some systems use other separators; e.g. quotation marks. Other systems only allow one tag to be entered at a time; in these cases you will have to repeat the process to add further tags.

'Official' Tags

Events and conferences increasingly are creating 'official' tags. These tags can then be used by participants for blog posts, photos of the event, presentation slides and other supporting materials and resources. This use of a consistent tag maximises the effectiveness of searching for resources relating to specific events.


  1. Tag (metadata), Wikipedia,
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