This means that the terms are written in a standardized form e.g. Lucene also performs a normalization when analyzing the data of which tokenization is a part. However, this does not apply if fixed terms consist of several words, such as “Christmas Eve.” Additional dictionaries are used for this, which can also be implemented in the Lucene code. The simplest way for tokenization to work is with the white space strategy: a term ends when a space occurs. These segments make it possible to search for terms (mostly single words). Segments are created from this amount of data using tokenization.
Apache lucene basics series#
Even if you break away from the level of bits and use content that can be read by humans instead, a document is still a series of characters: letters, punctuation marks, spaces. For a machine, a document is initially a collection of information. When documents are indexed, tokenization also takes place. For example, the field with the name title can have the value “Instructions for use for Apache Lucene.” So when creating the index, you can decide which metadata you want to include. These fields contain, for example, the name of the author, the title of the document, or the file name. However, from Lucene’s point of view, the documents themselves contain fields. The objects that Lucene works with are documents in every kind of form. To understand this, you have to go back one step. Developers decide which fields they want to include in the index during configuration. Lucene gives users the ability to configure this extraction individually. All terms must be taken from all the documents and stored in the index. In order to build an index, you first need to extract it. In principle, an inverted index is simply a table – the corresponding position is stored for each term.
Apache lucene basics pdf#
It not only searches HTML documents, but also works with e-mail and PDF files.Īn index – the heart of Lucene – is decisive for the search, since all terms of all documents are stored here. Lucene can also be used for archives, libraries, or even on your home desktop PC. This shows that Lucene is not solely used in the context of the world wide web, even if the searches are mostly found here. This means, quite simply: a program searches a series of text documents for one or more terms that the user has specified. Apache Solr and Elasticsearch are powerful extensions that give the search function even more possibilities. Originally, Lucene was written completely in Java, but now there are also ports to other programming languages. It is open source and free for everyone to use and modify.
Apache lucene basics software#
Lucene is a program library published by the Apache Software Foundation.
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