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Index
These are components that offer functionality for the index-service.
Indexes
There are two indexes with accompanying tools for constructing them.
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index-reverse is code for
word->documentindexes. There are two such indexes, one containing only document-word pairs that are flagged as important, e.g. the word appears in the title or has a high TF-IDF. This allows good results to be discovered quickly without having to sift through ten thousand bad ones first. -
index-forward is the
document->wordindex containing metadata about each word, such as its position. It is used after identifying candidate search results via the reverse index to fetch metadata and rank the results.
These indices rely heavily on the libraries/btree and libraries/array components.
Algorithms
- domain-ranking contains domain ranking algorithms.
- result-ranking contains logic for ranking search results by relevance.
Libraries
- index-query contains structures for evaluating search queries.
- index-journal contains tools for writing and reading index data.
Domain Ranking
Contains domain ranking algorithms. The domain ranking algorithms are based on the JGraphT library.
Two principal algorithms are available, the standard PageRank algorithm, and personalized pagerank; each are available for two graphs, the link graph and a similarity graph where each edge corresponds to the similarity between the sets of incident links to two domains, their cosine similarity acting as the weight of the links.
With the standard PageRank algorithm, the similarity graph does not produce anything useful, but something magical happens when you apply Personalized PageRank to this graph. It turns into a very good "vibe"-sensitive ranking algorithm.
It's unclear if this is a well known result, but it's a very interesting one for creating a ranking algorithm that is focused on a particular segment of the web.
Central Classes
- PageRankDomainRanker - Ranks domains using the PageRank or Personalized PageRank algorithm depending on whether a list of influence domains is provided.
Data sources
- LinkGraphSource - fetches the link graph
- InvertedLinkGraphSource - fetches the inverted link graph
- SimilarityGraphSource - fetches the similarity graph from the database
Note that the similarity graph needs to be precomputed and stored in the database for the similarity graph source to be available.
Useful Resources
Result Ranking
Contains various heuristics for deciding which search results are important with regard to a query. In broad strokes BM-25 is used, with a number of additional bonuses and penalties to rank the appropriate search results higher.