19.3.2.3 Technological and Infrastructure Requirements Implementing a recommendation service for BibSonomy required to tackle several problems, some of them we describe here.
First, having enough data available for recommendation algorithms to produce helpful recommendations is an important requirement one must address already in the design phase. The recommender needs access to the systems database and to what the user is currently posting (which could be accomplished, e.g., by (re)- loading recommendations using techniques like AJAX). Further data – like the full text of documents – could be supplied to tackle the cold-start problem (e.g., for content-based recommenders). The system must be able to handle large amounts of data, to quickly select relevant subsets and provide methods for preprocessing.
The available hardware and expected amount of data limits the choice of recommendation algorithms which can be used. Although some methods allow (partial) precomputation of recommendations, this needs extra memory and might not yield the same good results as online computation. Both hardware and network infrastructure must ensure short response times to deliver the recommendations to the user without too much delay. Together with a simple and non-intrusive user interface this ensures usability.
Further aspects which should be taken into account include implementation of logging of user events (e.g., clicking, key presses, etc.) to allow for efficient evaluation of the used recommendation methods in an online setting. Together with a live evaluation this also allows to tune the result selection strategies to dynamically choose the (currently) best recommendation algorithm for the user or resource at hand. The multiplexing of several available algorithms together with the simple inclusion of external recommendation services (by providing an open recommendation interface) is one of the recent developments in BibSonomy.
19.3.3 Tag Acquisition
The quality of tags can directly affect the recommendation performance of social tagging RS. Although folksonomies represent the “wisdom of crowds”, social tagging can present problems, such as tag sparsity (users tend to provide a constrained number of tags), polysemy (tags are subject to multiple interpretations), or tag idiosyncrasy (tags used for personal organization like “to read”, for example). All these problems can harm the quality of recommendations. For this reason, we consider alternative ways of acquiring tags. This will help us to better characterize the advantages and disadvantages of the social tagging process. We then examine the following tag acquisition methods:
• Expert Tagging: This approach usually relies on a small number of domain experts, who annotate resources using, mainly, structured vocabularies. Experts provide tags that are objective and cover multiple aspects. Pandora8 is a notable example of a system that uses experts for tagging music resources. The main advantage of using experts is the resulting well agreed tag vocabulary. This comes, of course, at the cost of manual work, which is both time consuming and expensive.
• Tagging based on annotation games: Games with a purpose (GWAP) [39], like the ESPGame9, is a breakthrough idea to use a game to employ humans for the purpose of annotation. Two players observe simultaneously the same image and are asked to enter tags until they both enter the same tag. Following the success of ESPGame, several others appeared (e.g., ListenGame10) in the