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From "Adriano Crestani (JIRA)" <>
Subject [jira] Commented: (LUCENE-1567) New flexible query parser
Date Tue, 09 Jun 2009 03:30:07 GMT


Adriano Crestani commented on LUCENE-1567:

I went through the new QP and listed what exactly needs to be changed:

QueryNode class has 2 methods: set(List<QueryNode>), add(List<QueryNode>) and
List<QueryNode> getChildren(). All the generics would be removed. I don't see any back
compatibility problem if we add generics in future, we could hardcode the type checking if
we release with 1.4 and any user impl of this class will need to do the same and follow the

ModifierQueryNode has an enum called Modifier with values MOD_NOT, MOD_NONE and MOD_REQ. An
enum can be almost completely reproduced on 1.4 using: 

final public static class Modifier implements Serializable {

   final public static Modifier MOD_NOT = new Modifier();

   final public static Modifier MOD_NOT = new Modifier();

   final public static Modifier MOD_NOT = new Modifier();

   private Modifier() { // empty constructor }

   // we might add some Enum methods, like name(), etc...


The only back compatibility problem I see when we change the Modifier to enum again is if
on the version 1.4 the user checks for Modifier.class.isEnum()...does anybody see any other
back-compatibility issue?

The last thing that will need to be changed is on the QueryBuilder and LuceneQueryBuilder.
The returns an Object and when LuceneQueryBuilder implements it, it specializes
the return to Query, which will start throwing Object instead if we change to 1.4. On this
case I don't see any back-compatibility issue also.

Regarding the new QP framework, I don't see any problem about back compatibility, because
Lucene will only be Java 1.5 on version 3.0, and back compatibility may be broken. But...

I would see nothing wrong with having a jdk 1.4 version if we were 100% compatible with the
old queryparser,
but since that is not the case, I don't think it is worth it. (the wrapper we built does not
support the case where users extend the old queryparser class and overwrite methods to add
new functionality)

I agree with Luis, if we only release the new QP framework 2.9, we will definitely brake the
back-compatiblity of the old QP, so, why not release the old and the new QP together on 2.9?

Suggestions? :)

Best Regards,
Adriano Crestani Campos
Adriano Crestani Campos

> New flexible query parser
> -------------------------
>                 Key: LUCENE-1567
>                 URL:
>             Project: Lucene - Java
>          Issue Type: New Feature
>          Components: QueryParser
>         Environment: N/A
>            Reporter: Luis Alves
>            Assignee: Grant Ingersoll
>         Attachments: lucene_trunk_FlexQueryParser_2009March24.patch, lucene_trunk_FlexQueryParser_2009March26_v3.patch,
> From "New flexible query parser" thread by Micheal Busch
> 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.

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