The purpose of this document is to outline plans for making Apache Lucene work as a more general drop-in component. It makes the assumption that this is an objective for the Lucene user and development community.

The best reference is htDig, though it is not quite as sophisticated as Lucene, it has a number of features that make it desirable. It however is a traditional c-compiled app which makes it somewhat unpleasant to install on some platforms (like Solaris!).

This plan is being submitted to the Lucene developer community for an initial reaction, advice, feedback and consent. Following this it will be submitted to the Lucene user community for support. Although, I'm (Andy Oliver) capable of providing these enhancements by myself, I'd of course prefer to work on them in concert with others.

While I'm outlaying a fairly large feature set, these can be implemented incrementally of course (and are probably best if done that way).

The goal is to provide features to Lucene that allow it to be used as a drop-in search engine. It should provide many of the features of projects like htDig while surpassing them with unique Lucene features and capabilities such as easy installation on and java-supporting platform, and support for document fields and field searches. And of course, a pragmatic software license.

To reach this goal we'll implement code to support the following objectives that augment but do not replace the current Lucene feature set.

• Document Location Independence - meaning mapping real contexts to runtime contexts. Essentially, if the document is at /var/www/htdocs/mydoc.html, I probably want it indexed as http://www.bigevilmegacorp.com/mydoc.html.
• Standard methods of creating central indicies - file system indexing is probably less useful in many environments than is *remote* indexing (for instance http). I would suggest that most folks would prefer that general functionality be supported by Lucene instead of having to write code for every indexing project. Obviously, if what they are doing is *special* they'll have to code, but general document indexing across web servers would not qualify.
• Document interpretation abstraction - currently one must handle document object construction via custom code. A standard interface for plugging in format handlers should be supported.
• Mime and file-extension to document interpretation mapping.

Crawlers are data source executable code. They crawl a file system, ftp site, web site, etc. to create the index. These standard crawlers may not make ALL of Lucene's functionality available, though they should be able to make most of it available through configuration.

Abstract Crawler

The AbstractCrawler is basically the parent for all Crawler classes. It provides implementation for the following functions/properties:

• index path - where to write the index.
• cui - create or update the index
• root context - the start of the pathname that should be replaced by the replace with property or dropped entirely. Example: /opt/tomcat/webapps
• replace with - when specified replaces the root context. Example: http://jakarta.apache.org.
• replacement type - the type of replace with path: relative, URL or path.
• location - the location to start indexing at.
• doctypes - only index documents with these doctypes. If not specified all registered mime-types are used. Example: "xml,doc,html"
• recursive - if not specified is turned off.
• level - optional level of directory or links to traverse. By default is assumed to be infinite. Recursive must be turned on or this is ignored. Range: 0 - Long.MAX_VALUE.
• SleeptimeBetweenCalls - can be used to avoid flooding a machine with too many requests
• RequestTimeout - kill the crawler request after the specified period of inactivity.
• IncludeFilter - include only items matching filter. (can occur multiple times)
• ExcludeFilter - exclude only items matching filter. (can occur multiple times)
• ExpandOnly - use but do not index items that match this pattern (regex?) (can occur multiple times)
• NoExpand - Index but do not follow the links in items that match this pattern (regex?) (can occur multiple times)
• MaxItems - stops indexing after x documents have been indexed.
• MaxMegs - stops indexing after x megs have been indexed.. (should this be in specific crawlers?)
• properties - in addition to the settings (probably from the command line) read this properties file and get them from it. Command line options override the properties file in the case of duplicates. There should also be an environment variable or VM parameter to set this.

FileSystemCrawler

This should extend the AbstractCrawler and support any additional options required for a file system index.

HTTP Crawler

Supports the AbstractCrawler options as well as:

• span hosts - Whether to span hosts or not, by default this should be no.
• restrict domains - (ignored if span hosts is not enabled). Whether all spanned hosts must be in the same domain (default is off).
• try directories - Whether to attempt directory listings or not (so if you recurse and go to /nextcontext/index.html this option says to also try /nextcontext to get the dir listing)
• map extensions - (always/default/never/fallback). Whether to always use extension mapping, by default (fallback to mime type), NEVER or fallback if mime is not available (default).
• ignore robots - ignore robots.txt, on or off (default - off)

A configurable registry of document types, their description, an identifier, mime-type and file extension. This should map both MIME -> factory and extension -> factory.

This might be configured at compile time or by a properties file, etc. For example:

Description	Identifier	Extensions	MimeType	DocumentFactory
"Word Document"	"doc"	"doc"	"vnd.application/ms-word"	POIWordDocumentFactory
"HTML Document"	"html"	"html,htm"		HTMLDocumentFactory

An interface for classes which create document objects for particular file types. Examples: HTMLDocumentFactory, DOCDocumentFactory, XLSDocumentFactory, XML DocumentFactory.

A class that maps standard fields from the DocumentFactories into *fields* in the Document objects they create. I suggest that a regular expression system or xpath might be the most universal way to do this. For instance if perhaps I had an XML factory that represented XML elements as fields, I could map content from particular fields to their fields or suppress them entirely. We could even make this configurable.

for example:

• htmldoc.properties
• suppress=*
• author=content:g/author\:\ ........................................./
• author.suppress=false
• title=content:g/title\:\ ........................................./
• title.suppress=false

In this example we map html documents such that all fields are suppressed but author and title. We map author and title to anything in the content matching author: (and x characters). Okay my regular expresions suck but hopefully you get the idea.

We might also consider eliminating the DocumentFactory entirely by making an AbstractDocument from which the current document object would inherit from. I experimented with this locally, and it was a relatively minor code change and there was of course no difference in performance. The Document Factory classes would instead be instances of various subclasses of AbstractDocument.

My inspiration for this is HTDig (http://www.htdig.org/). While this goes slightly beyond what HTDig provides by providing field mapping (where HTDIG is just interested in Strings/numbers wherever they are found), it provides at least what I would need to use this as a drop-in for most places I contract at (with the obvious exception of a default set of content handlers which would of course develop naturally over time).

I am able to certainly contribute to this effort if the development community is open to it. I'd suggest we do it iteratively in stages and not aim for all of this at once (for instance leave out the field mapping at first).

Anyhow, please give me some feedback, counter suggestions, let me know if I'm way off base or out of line, etc. -Andy