Hello, in my team at IBM we have used a different query parser than Lucene's in our products for quite a while. Recently we spent a significant amount of time in refactoring the code and designing a very generic architecture, so that this query parser can be easily used for different products with varying query syntaxes.
This work was originally driven by Andreas Neumann (who, however, left our team); most of the code was written by Luis Alves, who has been a bit active in Lucene in the past, and Adriano Campos, who joined our team at IBM half a year ago. Adriano is Apache committer and PMC member on the Tuscany project and getting familiar with Lucene now too. We think this code is much more flexible and extensible than the current Lucene query parser, and would therefore like to contribute it to Lucene. I'd like to give a very brief architecture overview here, Adriano and Luis can then answer more detailed questions as they're much more familiar with the code than I am. The goal was it to separate syntax and semantics of a query. E.g. 'a AND b', '+a +b', 'AND(a,b)' could be different syntaxes for the same query. We distinguish the semantics of the different query components, e.g. whether and how to tokenize/lemmatize/normalize the different terms or which Query objects to create for the terms. We wanted to be able to write a parser with a new syntax, while reusing the underlying semantics, as quickly as possible. In fact, Adriano is currently working on a 100% Lucene-syntax compatible implementation to make it easy for people who are using Lucene's query parser to switch. The query parser has three layers and its core is what we call the QueryNodeTree. It is a tree that initially represents the syntax of the original query, e.g. for 'a AND b': AND / \ A B The three layers are: 1. QueryParser 2. QueryNodeProcessor 3. QueryBuilder 1. The upper layer is the parsing layer which simply transforms the query text string into a QueryNodeTree. Currently our implementations of this layer use javacc. 2. The query node processors do most of the work. It is in fact a configurable chain of processors. Each processors can walk the tree and modify nodes or even the tree's structure. That makes it possible to e.g. do query optimization before the query is executed or to tokenize terms. 3. The third layer is also a configurable chain of builders, which transform the QueryNodeTree into Lucene Query objects. Furthermore the query parser uses flexible configuration objects, which are based on AttributeSource/Attribute. It also uses message classes that allow to attach resource bundles. This makes it possible to translate messages, which is an important feature of a query parser. This design allows us to develop different query syntaxes very quickly. Adriano wrote the Lucene-compatible syntax in a matter of hours, and the underlying processors and builders in a few days. We now have a 100% compatible Lucene query parser, which means the syntax is identical and all query parser test cases pass on the new one too using a wrapper. Recent posts show that there is demand for query syntax improvements, e.g improved range query syntax or operator precedence. There are already different QP implementations in Lucene+contrib, however I think we did not keep them all up to date and in sync. This is not too surprising, because usually when fixes and changes are made to the main query parser, people don't make the corresponding changes in the contrib parsers. (I'm guilty here too) With this new architecture it will be much easier to maintain different query syntaxes, as the actual code for the first layer is not very much. All syntaxes would benefit from patches and improvements we make to the underlying layers, which will make supporting different syntaxes much more manageable. So if there is interest we would like to contribute this work to Lucene. I think the amount of code (~6K LOC) is higher than in a usual patch, but also lower than some contrib modules. So I'm not sure if we could contribute it as a normal patch or maybe a software grant? We could also maybe think about adding it as a contrib module initially, and if people like it move it to the core at a later point. I'd actually prefer this approach over committing to the core directly, as it would make it easier to make Luis and Adriano contrib committers on the new module, which of course makes sense as nobody knows the code better than they do. -Michael --------------------------------------------------------------------- To unsubscribe, e-mail: java-dev-unsubscr...@lucene.apache.org For additional commands, e-mail: java-dev-h...@lucene.apache.org
