Lucene is a high-performance, scalable information retrieval (search) library developed by Apache Foundation, which can be used for implementing free-text search in web applications. Lucene provides a simple-to-use API, which will provide powerful indexing and searching capability to your web application. To read more about Lucene visit http://lucene.apache.org/.
The most important components of the Lucene search library are explained as follows:
Index: Lucene index is the data store that holds all the indexed documents; queries are executed against the index to fetch the documents.
Document: A document is the default building block for a Lucene index; documents can be compared to records in a table. Each document holds a number of fields upon which queries can be executed.
Field: Each Lucene document comprises of one or more fields; it is not necessary that all the fields are indexed, fields can also be stored without indexing.