IMAPEXT T. Sirainen
Internet-Draft April 16, 2009
Intended status: Standards Track
Expires: October 18, 2009
IMAP4 Extension for Fuzzy Search
draft-ietf-morg-fuzzy-search-00
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Abstract
This document describes an IMAP protocol extension enabling server to
perform searches with inexact string matching and assigning relevancy
scores for matched messages.
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Note
A revised version of this draft document will be submitted to the RFC
editor as a Proposed Standard for the Internet Community. Discussion
and suggestions for improvement are requested, and should be sent to
morg@ietf.org.
1. Conventions used in this document
In examples, "C:" indicates lines sent by a client that is connected
to a server. "S:" indicates lines sent by the server to the client.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [Kwds].
2. Introduction
When humans perform searches in IMAP clients, they typically want to
see the most relevant search results first. IMAP servers are able to
do this in the most efficient way when they're free to internally
decide how searches should match messages. This document describes a
new SEARCH=FUZZY extension that provides such functionality.
3. The FUZZY Search Key
FUZZY search key takes another search key as its argument. For this
search key server is allowed to perform all string matching in an
implementation-defined manner instead of performing a strict
substring search as requred by [RFC3501]. It MUST NOT modify the
behavior of search keys that don't compare strings. For example:
C: A01 SEARCH FUZZY (SUBJECT "Helo mom" SMALLER 5000 SEEN)
S: * SEARCH 1 5 10
S: A01 OK Search completed.
Besides matching messages with subject "Helo mom", the above search
may also match messages with subjects "Hello mom", "Hello mother", or
anything else the server decides that might be a good match.
However, the result MUST NOT contain messages that don't have a \Seen
flag set or whose size is 5000 bytes or more.
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4. Relevancy Scores for Search Results
The server SHOULD assign a search relevancy score for each matched
message when the FUZZY search key is given. This allows the client
to show the most relevant search results first. Relevancy scores are
meaningful only when compared to other relevancy scores from the same
server. This means that this specification doesn't define a "best
relevancy" score. Instead the values are represented by an 32 bit
integer and implementations can decide how high values they want to
use. For example some implementations might decide to use only
values 1-5 while others might decide to use the full 32 bit range.
If server advertises the ESEARCH capability as defined by [ESEARCH],
the relevancy scores can be retrieved using the new RELEVANCY return
option for SEARCH:
C: A02 SEARCH RETURN (RELEVANCY ALL) FUZZY TEXT "Helo"
S: * ESEARCH (TAG "A02") ALL 1,5,10 RELEVANCY (4 107 42)
S: A02 OK Search completed.
RELEVANCY return option SHOULD NOT be used unless FUZZY search key is
also given, otherwise servers MAY decide to give the same relevancy
score to all messages.
5. Extensions to SORT
If server advertises the SORT capability as defined by [SORT], the
results can be sorted by the new RELEVANCY sort criteria:
C: A03 SORT (RELEVANCY) UTF-8 FUZZY SUBJECT "Helo"
S: * SORT 5 10 1
S: A03 OK Sort completed.
The message with the highest score is returned first. As with
RELEVANCY return option, RELEVANCY sort criteria SHOULD NOT be used
unless FUZZY search key is also given.
[[anchor6: TODO: Describe also RELEVANCY with ESORT.]]
6. Formal Syntax
The following syntax specification uses the augmented Backus-Naur
Form (BNF) as described in [ABNF]. It includes definitions from
[RFC3501], [IMAP-ABNF] and [SORT].
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capability =/ "SEARCH=FUZZY"
score = number
;; <number> from [RFC3501]
score-list = "(" [score *(SP score)] ")"
search-key =/ "FUZZY" SP search-key
search-return-data =/ "RELEVANCY" SP score-list
;; Conforms to <search-return-data>, from [IMAP-ABNF]
search-return-opt =/ "RELEVANCY"
;; Conforms to <search-return-opt>, from [IMAP-ABNF]
sort-key =/ "RELEVANCY"
7. Security Considerations
This document is believed not to have any security implications.
8. IANA Considerations
IMAP4 capabilities are registered by publishing a standards track or
IESG approved experimental RFC. The registry is currently located
at:
http://www.iana.org/assignments/imap4-capabilities
This document defines the X-DRAFT-I00-SEARCH=FUZZY [[anchor7: Note to
RFC Editor: fix before publication]] IMAP capability. IANA is
requested to add it to the registry.
9. Acknowledgements
Alexey Melnikov has helped with this document.
10. Normative References
[ABNF] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 5234, January 2008.
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[ESEARCH] Melnikov, A. and D. Cridland, "IMAP4 Extension to SEARCH
Command for Controlling What Kind of Information Is
Returned", RFC 4731, November 2006.
[IMAP-ABNF]
Melnikov, A. and C. Daboo, "Collected Extensions to IMAP4
ABNF", RFC 4466, April 2006.
[Kwds] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997.
[RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
4rev1", RFC 3501, March 2003.
[SORT] Crispin, M. and K. Murchison, "Internet Message Access
Protocol - SORT and THREAD Extensions", RFC 5256,
June 2008.
Author's Address
Timo Sirainen
Email: tss@iki.fi
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