Web 2.0 Series: Social Bookmarking
Social bookmarking occurs on web based services where shared lists of user-created Internet bookmarks are displayed. Social bookmarking sites generally organize their content using tags and are an increasingly popular way to locate, classify, rank, and share Internet resources through the practice of tagging, and inferences drawn from grouping and use of such tags. Both social bookmarking and tagging originated with the launch of a web site called del.icio.us in approximately 2003.
In such a system, users store lists of Internet resources, usually out of a personal interest in these resources. Often, these lists are publicly accessible, although some social bookmarking systems allow for privacy on a bookmark by bookmark basis. They also categorize their resources by the use of informally assigned, user-defined keywords or tags (see folksonomy). Most social bookmarking services allow users to search for bookmarks which are associated with given "tags", and rank the resources by the number of users which have bookmarked them. Many social bookmarking services also have implemented algorithms to draw inferences from the tag keywords that are assigned to resources by examining the clustering of particular keywords, and the relation of keywords to one another.
Such a system has several advantages over traditional automated resource location and classification software, such as search engine spiders. All tag-based classification of Internet resources (such as web sites) is done by human beings, who understand the content of the resource, as opposed to software which algorithmically attempts to determine the meaning of a resource. Additionally, as people bookmark resources that they find useful, resources that are of more use are bookmarked by more users. Thus, such a system will "rank" a resource based on its perceived utility. This is a more useful metric for end users than other systems which rank resources based on the number of external links pointing to it.
For example, imagine two resources: the first has many hyperlinks pointing to it, but is of limited use; the second has relatively few hyperlinks to it, but is of much more use to end users. Traditional search engines such as Google would tend to rank the first resource higher, while a social bookmarking system, whose rank is based on user evaluation of a resource's usefulness, would rank the second higher.
Since the classification and ranking of resources is a continuously evolving process, many social bookmarking services allow users to subscribe to syndication feeds (see RSS) based on tags, or collection of tag terms. This allows subscribers to become aware of new resources for a given topic, as they are noted, tagged, and classified by other users.
There are drawbacks to such tag-based systems as well: no standard set of keywords, no standard for the structure of such tags (e.g. singular vs. plural, capitalization, etc.), mistagging due to spelling errors, tags that can have more than one meaning, unclear tags due to synonym/antonym confusion, highly unorthodox and "personalized" tag schemas from some users, and no mechanism for users to indicate hierarchical relationships between tags (e.g. a site might be labeled as both cheese and cheddar, with no mechanism that might indicate that cheddar is a refinement or sub-class of cheese).
The separate (but related) tagging and social bookmarking services are, however, evolving rapidly, and these shortcomings will likely either be addressed in the near future or shown not to be relevant to these services.