Dr. Dobb's Journal - May 2008 - (Page 46)

d05zeid_p3db 3/18/08 8:42 AM Page 46 State of the Art GETTING BETTER SEARCH RESULTS method is Boolean, Probabilistic, or Vector. For a Boolean retrieval method, Ri is a scalar 1 for all i. In other words, a Boolean method only retrieves objects that exactly match the query: Ri = 1 for all i For a probabilistic retrieval method, Ri equals ρ(Q|Oi), which is the probability that a user’s query is met by retrieved object Oi. A probabilistic method retrieves information based on some threshold probability that the object is what the user wants: Ri = ρ(Q|Oi) for all i • Internal criteria are criteria derived from the relationships determined during the retrieval process. • External criteria are criteria determined in a new step unrelated to the retrieval process. Of course, combinations of internal and external criteria can also be used. For best-match retrieval methods, the objects can be displayed in order according to their relationship to the query. Objects with higher probabilities or higher correlation values are displayed first. The relationships are used as the criteria for displaying the objects. For exact-match retrieval methods, internal criteria do not provide a way to display the results because all retrieved objects have a relationship of 1. External criteria are often used to display the results of search engines. Perhaps the best-known example of external display criteria is the PageRank method used by Google that ranks pages according to how many other pages are linked to it. Other methods include the Hub-Threshold Kleinberg algorithm. I use the term Pi to generally represent ranking methods. Regardless of which kind of ranking criteria is used, there is often also a display threshold. Retrieved objects that have a ranking below the display threshold are not shown to users. An object with a very low ranking is thought to be irrelevant and its relationship with the query is thought to be random, rather than due to any relationship that would be significant to users. For a vector space retrieval method, Ri equals (Q,Oi), which is the correlation between a user’s query and some object Oi. A vector space method retrieves information that is similar to another object that the user desires: Ri = (Q,Oi) for all i In addition to relationships between a query and the retrieved objects, note that there are relationships between various retrieved objects, represented by the arrows Rik between objects Oi and Ok. I make use of this fact for post-process filtering. Information Display Once the information objects are retrieved from the domain, they must be displayed to users. There are two types of criteria that can be used for this display in order to rank the retrieved objects. Post-Retrieval Filtering What I propose is another step after retrieval and display to further refine the results and reduce the number of retrieved objects to one that is reasonable to examine. There are several ways this can be accomplished using combinations of object filters, new query filters, negative query filters, threshold filters, and object relationship filters. Object filtering is the process of letting users eliminate individual objects or whole sets of objects from the user information domain DU. This can be done by letting users specify objects to remove or categories of objects to remove. The removal process is dependent on the type of information being retrieved. When the retrieved objects are files, the criteria used to remove objects might be file name, location (path name), size, modification date, or creation date. With regard to CodeMatch, the general file filtering, specific file filtering, and folder filtering are examples of object filtering. In the case of a search engine, a user could specify to remove certain websites from the search results, or users could specify certain web page names to be removed. Users could also click on certain specific pages to be removed. New query filtering refers to using a new query on the retrieved user domain DU to create a new domain DU' that is a subset of DU. Some search engines provide this kind of filtering by allowing the user to further search the retrieved results with a new Boolean expression of keywords. Negative query filtering refers to applying a query to the retrieved information in order to eliminate objects. For instance, suppose the 46 Dr. Dobb’s Journal l www.ddj.com l May 2008 http://www.entrek.com http://www.entrek.com http://www.ddj.com

Table of Contents Feed for the Digital Edition of Dr. Dobb's Journal - May 2008

Dr. Dobb's Journal - May 2008 Contents Friday Night Fish Fry Alia Vox Developer Diaries Software Development Goes to the Movies Cat: A Functional Stack-Based Little Language Mojax: Mobile Ajax Framework Kernel-Mode Databases Getting Better Search Results Effective Concurrency The Agile Edge

Dr. Dobb's Journal - May 2008

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