Web2.0 in the light of HCIVisualizing Tags over TimeCS 260October 25, 2006Hannes HesseWeb 2.0 is the network as platform, spanning all connected devices; Web 2.0 applications are those that make the most of the intrinsic advantages of that platform: delivering software as a continually-updated service that gets better the more people use it, consuming and remixing data from multiple sources, including individual users, while providing their own data and services in a form that allows remixing by others, creating network effects through an "architecture of participation," and going beyond the page metaphor of Web 1.0 to deliver rich user experiences.What?Tagsvs. Taxonomies/articles/cats all articles on cats /articles/africa all articles on Africa /articles/africa/cats all articles on African cats /articles/cats/africa all articles on cats from Africa Taxonomieshierarchical, exclusiveTagsnon-hierarchical, inclusive Each choice reflects a decision about the relative importance of each characteristic. Folder names and levels are in themselves informative, in that, like tags, they describe the information held within them (Jones et al. 2005). Folders like 1. and 2. make central the fact that the folders are about “cats” and “africa” respectively, but elide all information about the other category. 3. and 4. organize the files by both categories, but establish the first as primary or more salient, and the second as secondary or more specific. However, looking in 3. for a file in 4. will be fruitless, and so checking multiple locations becomes necessary. Despite these limitations, there are several good reasons to impose such a hierarchy. Though there can be too many folders in a hierarchy, especially one created haphazardly, an efficiently organized file hierarchy neatly and unambiguously bounds a folder’s contents. Unlike a keyword-based search, wherein the seeker cannot be sure that a query has returned all relevant items, a folder hierarchy assures the seeker that all the files it contains are in one stable place. In contrast to a hierarchical file system, a non-exclusive, flat tagging system could, unlike the system described above, identify such an article as being about a great variety of things simultaneously, including africa and cats, as well as animals more generally, and cheetahs, more specifically. Like a Venn diagram, the set of all the items marked cats and those marked africa would intersect in precisely one way, namely, those documents that are tagged as being about African cats. Even this is not perfect, however. For example, a document tagged only cheetah would not be found in the intersection of africa and cats, though it arguably ought to; like the foldering example above, a seeker may still need to search multiple locations. “cats” “africa” “cats” AND “africa” Figure 1. A Venn diagram showing the intersection of “cats” and “africa”. Looking at it another way, tagging is like filtering; out of all the possible documents (or other items) that are tagged, a filter (i.e. a tag) returns only those items tagged with that tag. Depending on the implementation and query, a tagging system can, instead of providing the intersection of tags (thus, filtering), provide the union of tags; that is, all the items tagged with any of the given tags, rather than all of them. From a user perspective, navigating a tag system is similar to conducting keyword-based searches; regardless of the implementation, users are providing salient, descriptive terms in order to retrieve a set of applicable items. 2.1 Semantic and Cognitive Aspects of Classification Both tagging systems and taxonomies are beset by many problems that exist as a result of the necessarily imperfect, yet natural and evolving process of creating semantic relations between words and their referents. Three of these problems are polysemy, synonymy, and basic level variation. A polysemous word is one that has many (“poly”) related senses (“semy”). For example, a “window” may refer to a hole in the wall, or to the pane of glass that resides within it (Pustejovsky 1995). In practice, polysemy dilutes query results by returning related but potentially inapplicable items. Superficially, polysemy is similar to homonymy, where a word has multiple, unrelated meanings. However, homonymy is less a problem because homonyms can be largely ruled out in a tag-based search through the addition of a related term with which the unwanted homonym would not appear. There are, of course, cases where homonyms are semantically related but not polysemous; for example, searching for employment at Apple may be problematic because of conflicts with the CEO’s surname. Synonymy, or multiple words having the same or closely related meanings, presents a greater problem for tagging systems because inconsistency among the terms used in tagging can make it very difficult for one to be sure that all the relevant items have been found. It is difficult for a tagger to be consistent in the terms chosen for tags; for example, items about television may be tagged either television or tv . This problem is compounded in a collaborative system, where all taggers either need to widely agree on a convention, or else accept that they must issue multiple or more complex queries to cover many possibilities. Synonymy is a significant problem because it is impossible to know how many items “out there” one would have liked one’s query to have retrieved, but didn’t. Relatedly, plurals and parts of speech and spelling can stymie a tagging system. For example, if tags ca t and cats are distinct, then a query for one will not retrieve both, unless the system has the capability to perform such replacements built into it. Reflecting the cognitive aspect of hierarchy and categorization, the “basic level” problem is that related terms that describe an item vary along a continuum of specificity ranging from very general to very specific; as discussed above,