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38 lines
1.7 KiB
Markdown
38 lines
1.7 KiB
Markdown
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# Search Engine
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The Search Engine powers the Search input in the note list and the Goto Anything dialog.
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## Search algorithm
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### Discretely using only the most critical parameter in sorting
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Sorting occurs as the Search Engine processes results, after searching for and weighting these results.
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Parameters include fuzziness, title matching, weight (based on BM25 and age), the completed status of to-dos, and the note's age.
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The Search Engine uses only the first relevant parameter to determine the order, rather than a weighted average.
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In effect, this means search results with note title matches will appear above all results that only matched the note body,
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regardless of weight or other parameters.
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### Determining weight as a sorting parameter
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The Search Engine determines the weight parameter using both [BM25](https://en.wikipedia.org/wiki/Okapi_BM25)
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and the number of days since last user update.
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#### BM25
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The Search Engine determines BM25 based on "term frequency-inverse document frequency."
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The "TF–IDF" value increases proportionally to the number of times a word appears in the document
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and is offset by the number of documents in the corpus that contain the word, which helps to adjust
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for the fact that some words appear more frequently in general.
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BM25 returns weight zero for a search term that occurs in more than half the notes.
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So terms that are abundant in all notes to have zero relevance w.r.t. BM25.
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#### Days since last user update
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Sorting increases the BM25 weight by the inverse number of days since the note was updated.
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Recent notes will, therefore, be weighted highly in the search results.
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This time-based weight decays logarithmically, becoming less of a factor than BM25 after months have passed.
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