Apache lucene and text meaning - lucene

I have a question about searching process in lucene/.
I use this code for search
Directory directory = FSDirectory.GetDirectory(#"c:\index");
Analyzer analyzer = new StandardAnalyzer();
QueryParser qp = new QueryParser("content", analyzer);
qp.SetDefaultOperator(QueryParser.Operator.AND);
Query query = qp.Parse(search string);
In one document I've set "I want to go shopping" for a field and in other document I've set "I wanna go shopping".
the meaning of both sentences is same!
is there any good solution for lucene to understand meaning of sentences or kind of normalize the scentences ? for example save the fields like "I wanna /want to/ go shopping" and remove the comment with regexp in result.

Lucene provides filter to normalize words and even map similar words.
PorterStemFilter -
Stemming allows words to be reduced to their roots.
e.g. wanted, wants would be reduced to root want and search for any of those words would match the document.
However, wanna does not reduce to root want. So it may not work in this case.
SynonymFilter -
would help you to map words similar in a configuration file.
so wanna can be mapped to want and if you search for either of those, the document must match.
you would need to add the filters in your analysis chain.

Related

How to search in lucene where there is only a single token for a field

I am creating an index where the documents are only a single term.
I am indexing domain names, so the field "domain" would look like:
example.com
thisiscool.com
justtesting.org
cnn.com
I am creating my search terms etc. programatically, and because all my document field is just a single term, it appears as though my searches won't work as they are since there is only a single term and if I add multiple terms in a boolean query it will never find anything.
How should I be searching given I have only a single term? I want to make this as efficient as possible.
Query term = new TermQuery("domain", "this")
Query term2 = new TermQuery("domain", "cool")
// add to boolean query
bq.add(term, Occur.MUST)
bq.add(term2, Occur.MUST)
indexSearcher.search(bq, 100)
I was expecting to get "thisiscool.com" back, but I get 0 hits. My guess is because lucene can't break things down into tokens, so it will never find any document that has both tokens "this" and "cool".
How should I be searching given this scenerio?
Apply a wildcard to your search clause.
Query term = new TermQuery("domain", "this*");
Query term2 = new TermQuery("domain", "cool*"); // *cool* won't work sadly
However, that might not work because the logic is going to result in a query like this, where the domain has to begin with "this" as well as "cool"
bq.add(term, Occur.MUST)
bq.add(term2, Occur.MUST)
=> +domain:this* +domain:cool*
Query term = new TermQuery("domain", "this*cool*");
=> +domain:this*cool* // probably gets hits
If you're using newer versions then you can use regular expressions in queries:
http://lucene.apache.org/core/6_6_0/core/org/apache/lucene/util/automaton/RegExp.html
The above example isn't actually how you should do this. I tested it out, and it doesn't even really work. What you'll want to do is build specialized queries, such as PrefixQuery, WildcardQuery, or RegexpQuery.
Additionally, if you're not using QueryParser or something that takes an Analyzer, queries have to match exactly to what's in your index. If domain is a TextField it might have been lowercased or had something else happen to it, so you'll need to know that too.
I'd just use regex.
RegExp r = new RegExp("this.*cool");
Query q = new RegexpQuery(new Term("domain", r.toString()));
It can be slow, but if you don't prefix with any char it should be perfectly fine. I'm also not entirely sure how to ignore case with this, but that might be default.

Space issue in Lucene.NET C#

I want to search sentence which has space in full text search.
Ex: Tom is a very good boy in class.
I want to Search the key word "very good".
I'm using white space tokenizer to create/search index. But it is not finding the keyword if it is separated by space.
Code:
Query searchItemQuery = new WildcardQuery(new Term(string-field-name, searchkeyword.ToLower()));
I've tried with split but it is not working properly.
Do anyone suggest me a solution for this problem?
Thanks,
Vijay
Since, you are working with tokenized string, every word is a separate term.
In order too find a phrase consisting of multiple terms, you would need to use PhraseQuery instead of WildcardQuery.
Like this:
PhraseQuery phraseQuery = new PhraseQuery();
phraseQuery.Add(new Term(string-field-name, "very"));
phraseQuery.Add(new Term(string-field-name, "good"));
Note also, that you are using wildcard query. Wildcards in phrase query are a bit complex. Check this post for details: Lucene - Wildcards in phrases
And finally, I would suggest to consider using QueryParser instead of constructing query manually.

How can I perform a fuzzy search for all words provided in a Lucene.net search

I am trying to teach myself Lucene.Net to implement on my site. I understand how to do almost everything I need except for one issue. I am trying to figure out how to allow a fuzzy search for all search terms in a search string.
So for example if I have a document with the string The big red fox, I am trying to get bag fix to match it.
The problem is, it seems like in order to perform fuzzy searches, I have to add ~ to every search term the user enters. I am unsure of the best way to go about this. Right now I am attempting this by
string queryString = "bag rad";
queryString = queryString.Replace("~", string.Empty).Replace(" ", "~ ") + "~";
The first replace is due to Lucene.Net throwing an exception if the search string has a ~ already, apparently it can't handle ~~ in a phrase. This method works, but it seems like it will get messy if I start adding fuzzy weight values.
Is there a better way to default all words to allow for fuzzyness?
You might want to index your documents as bi-grams or tri-grams. Take a look at the CJKAnalyzer to see how they do it. You will want to download the source and look at the source.

Using MultiFieldQueryParser

Am using MultiFieldQueryParser for parsing strings like a.a., b.b., etc
But after parsing, its removing the dots in the string.
What am i missing here?
Thanks.
I'm not sure the MultiFieldQueryParser does what you think it does. Also...I'm not sure I know what you're trying to do.
I do know that with any query parser, strings like 'a.a.' and 'b.b.' will have the periods stripped out because, at least with the default Analyzer, all punctuation is treated as white space.
As far as the MultiFieldQueryParser goes, that's just a QueryParser that allows you to specify multiple default fields to search. So with the query
title:"Of Mice and Men" "John Steinbeck"
The string "John Steinbeck" will be looked for in all of your default fields whereas "Of Mice and Men" will only be searched for in the title field.
What analyzer is your parser using? If it's StopAnalyzer then the dot could be a stop word and is thus ignored. Same thing if it's StandardAnalyzer which cleans up input (includes removing dots).
(Repeating my answer from the dupe. One of these should be deleted).
The StandardAnalyzer specifically handles acronyms, and converts C.F.A. (for example) to cfa. This means you should be able to do the search, as long as you make sure you use the same analyzer for the indexing and for the query parsing.
I would suggest you run some more basic test cases to eliminate other factors. Try to user an ordinary QueryParser instead of a multi-field one.
Here's some code I wrote to play with the StandardAnalyzer:
StringReader testReader = new StringReader("C.F.A. C.F.A word");
StandardAnalyzer analyzer = new StandardAnalyzer();
TokenStream tokenStream = analyzer.tokenStream("title", testReader);
System.out.println(tokenStream.next());
System.out.println(tokenStream.next());
System.out.println(tokenStream.next());
The output for this, by the way was:
(cfa,0,6,type=<ACRONYM>)
(c.f.a,7,12,type=<HOST>)
(word,13,17,type=<ALPHANUM>)
Note, for example, that if the acronym doesn't end with a dot then the analyzer assumes it's an internet host name, so searching for "C.F.A" will not match "C.F.A." in the text.

How to make Lucene match all words in query?

I am using Lucene to allow a user to search for words in a large number of documents. Lucene seems to default to returning all documents containing any of the words entered.
Is it possible to change this behaviour? I know that '+' can be use to force a term to be included but I would like to make that the default action.
Ideally I would like functionality similar to Google's: '-' to exclude words and "abc xyz" to group words.
Just to clarify
I also thought of inserting '+' into all spaces in the query. I just wanted to avoid detecting grouped terms (brackets, quotes etc) and potentially breaking the query. Is there another approach?
This looks similar to the Lucene Sentence Search question. If you're interested, this is how I answered that question:
String defaultField = ...;
Analyzer analyzer = ...;
QueryParser queryParser = new QueryParser(defaultField, analyzer);
queryParser.setDefaultOperator(QueryParser.Operator.AND);
Query query = queryParser.parse("Searching is fun");
Like Adam said, there's no need to do anything to the query string. QueryParser's setDefaultOperator does exactly what you're asking for.
Why not just preparse the user search input and adjust it to fit your criteria using the Lucene query syntax before passing it on to Lucene. Alternatively, you could just create some help documentation on how to use the standard syntax to create a specific query and let the user decide how the query should be performed.
Lucene has a extensive query language as described here that describes everything you want except for + being the default but that's something you can simple handle by replacing spaces with +. So the only thing you need to do is define the format you want people to enter their search queries in (I would strongly advise to adhere to the default Lucene syntax) and then you can write the transformations from your own syntax to the Lucene syntax.
The behavior is hard-coded in method addClause(List, int, int, Query) of class org.apache.lucene.queryParser.QueryParser, so the only way to change the behavior (other than the workarounds above) is to change that method. The end of the method looks like this:
if (required && !prohibited)
clauses.addElement(new BooleanClause(q, BooleanClause.Occur.MUST));
else if (!required && !prohibited)
clauses.addElement(new BooleanClause(q, BooleanClause.Occur.SHOULD));
else if (!required && prohibited)
clauses.addElement(new BooleanClause(q, BooleanClause.Occur.MUST_NOT));
else
throw new RuntimeException("Clause cannot be both required and prohibited");
Changing "SHOULD" to "MUST" should make clauses (e.g. words) required by default.