rfc2654.txt
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Network Working Group R. HedbergRequest for Comments: 2654 CatalogixCategory: Experimental B. Greenblatt Directory Tools and Application Services, Inc. R. Moats AT&T M. Wahl Innosoft International, Inc. August 1999 A Tagged Index Object for use in the Common Indexing ProtocolStatus of this Memo This memo defines an Experimental Protocol for the Internet community. It does not specify an Internet standard of any kind. Discussion and suggestions for improvement are requested. Distribution of this memo is unlimited.Copyright Notice Copyright (C) The Internet Society (1999). All Rights Reserved.Abstract This document defines a mechanism by which information servers can exchange indices of information from their databases by making use of the Common Indexing Protocol (CIP). This document defines the structure of the index information being exchanged, as well as the appropriate meanings for the headers that are defined in the Common Indexing Protocol. It is assumed that the structures defined here can be used by X.500 DSAs, LDAP servers, Whois++ servers, CSO Ph servers and many others.Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Background . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Object . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4. The Tagged Index Object . . . . . . . . . . . . . . . . . . . . 5 4.1. The Agreement . . . . . . . . . . . . . . . . . . . . . . . . 5 4.2. Content Type . . . . . . . . . . . . . . . . . . . . . . . . 8 4.3 Tagged Index BNF . . . . . . . . . . . . . . . . . . . . . . . 9 4.3.1. Header Descriptions . . . . . . . . . . . . . . . . . . . .10 4.3.2. Tokenization types . . . . . . . . . . . . . . . . . . . .11 4.3.3. Tag Conventions . . . . . . . . . . . . . . . . . . . . . .11 4.4. Incremental Indexing . . . . . . . . . . . . . . . . . . . .12Hedberg, et al. Experimental [Page 1] RFC 2654 Tagged Index Object for use in CIP August 1999 5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . .13 5.1 The original database . . . . . . . . . . . . . . . . . . . .13 5.1.1 "complete" consistency based full update . . . . . . . . . .14 5.1.2 "tag" consistency based full update . . . . . . . . . . . .14 5.1.3 "unique" consistency based full update . . . . . . . . . . .15 5.2 First update . . . . . . . . . . . . . . . . . . . . . . . . .16 5.2.1 "complete" consistency based incremental update . . . . . .16 5.2.2 "tag" consistency based incremental update . . . . . . . .17 5.2.3 "unique" consistency based incremental update . . . . . . .17 5.3 Second update . . . . . . . . . . . . . . . . . . . . . . . .18 5.3.1 "complete" consistency based incremental update . . . . . .18 5.3.2 "tag" consistency based incremental update . . . . . . . . .19 5.3.3 "unique" consistency based incremental update . . . . . . .20 6. Aggregation . . . . . . . . . . . . . . . . . . . . . . . . . .21 6.1 Aggregation of Tagged Index Objects . . . . . . . . . . . . .21 7. Security Considerations . . . . . . . . . . . . . . . . . . . .21 8. References . . . . . . . . . . . . . . . . . . . . . . . . . .22 9. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . .23 Full Copyright Statement . . . . . . . . . . . . . . . . . . . . .241. Introduction The Common Indexing Protocol (CIP) as defined in [1] proposes a mechanism for distributing searches across several instances of a single type of search engine to create a global directory. CIP provides a scalable, flexible scheme to tie individual databases into distributed data warehouses that can scale gracefully with the growth of the Internet. CIP provides a mechanism for meeting these goals that is independent of the access method that is used to access the data that underlies the indices. Separate from CIP is the definition of the Index Object that is used to contain the information that is exchanged among Index Servers. One such Index Object that has already been defined is the Centroid that is derived from the Whois++ protocol [2]. The Centroid does not meet all the requirements for the exchange of index information amongst information servers. For example, it does not support the notion of incremental updates natively. For information servers that contain millions of records in their database, constant exchange of complete dredges of the database is bandwidth intensive. The Tagged Index Object is specifically designed to support the exchange of index update information. This design comes at the cost of an increase in the size of the index object being exchanged. The Centroid is also not tailored to always be able to give boolean answers to queries. In the Centroid Model, "an index server will take a query in standard Whois++ format, search its collections of centroids and other forward information, determine which servers hold records which may fill that query, and thenHedberg, et al. Experimental [Page 2] RFC 2654 Tagged Index Object for use in CIP August 1999 notifies the user's client of the next servers to contact to submit the query." [2] Thus, the exchange of Centroids amongst index servers allows hints to be given about which information server actually contains the information. The Tagged Index Object labels the various pieces of information with identifiers that tie the individual object attributes back to an object as a whole. This "tagging" of information allows an index server to be more capable of directing a specific query to the appropriate information server. Again, this feature is added to the Tagged Index Object at the expense of an increase in the size of the index object.2. Background The Lightweight Directory Access Protocol (LDAP) is defined in [3], and it defines a mechanism for accessing a collection of information arranged hierarchically in such a way as to provide a globally distributed database which is normally called the Directory Information Tree (DIT). Some distinguishing characteristics of LDAP servers are that normally, several servers cooperate to manage a common subtree of the DIT. LDAP servers are expected to respond to requests that pertain to portions of the DIT for which they have data, as well as for those portions for which they have no information in their database. For example, the LDAP server for a portion of the DIT in the United States (c=US) must be able to provide a response to a Search operation that pertains to a portion of the DIT in Sweden (c=se). Normally, the response given will be a referral to another LDAP server that is expected to be more knowledgeable about the appropriate subtree. However, there is no mechanism that currently enables these LDAP servers to refer the LDAP client to the supposedly more knowledgeable server. Typically, an LDAP (v3) server is configured with the name of exactly one other LDAP server to which all LDAP clients are referred when their requests fall outside the subtree of the DIT for which that LDAP server has knowledge. This specification defines a mechanism whereby LDAP server can exchange index information that will allow referrals to point towards a clearly accurate destination. The X.500 series of recommendations defines the Directory Information Shadowing Protocol (DISP) [4] which allows X.500 DSAs to exchange information in the DIT. Shadowing allows various information from various portions of the DIT to be replicated amongst participating DSAs. The design point of DISP is improved at the exchange of entire portions of the DIT, whereas the design point of CIP and the Tagged Index Object is optimized at the exchange of structural index information about the DIT, and improving the performance of tree navigation amongst various information servers. The Tagged Index Object is more appropriate for the exchange of index information than is DISP. DISP is more targeted at DIT distribution and faultHedberg, et al. Experimental [Page 3] RFC 2654 Tagged Index Object for use in CIP August 1999 tolerance. DISP is thus more appropriate for the exchange of the data in order to spread the load amongst several information servers. DISP is tailored specifically to X.500 (and other hierarchical directory systems), while the Tagged Index Object and CIP can be used in a wide variety of information server environments. While DISP allows an individual directory server to collect information about large parts of the DIT, it would require a huge database to collect all the replicas for a significant portion of the DIT. Furthermore, as X.525 states: "Before shadowing can occur, an agreement, covering the conditions under which shadowing may occur is required. Although such agreements may be established in a variety of ways, such as policy statements covering all DSAs within a given DMD ...", where a DMD is a Directory Management Domain. This is owing to the case that the data in the DIT is being exchanged amongst DSA rather than only the information required to maintain an Index. In many environments such an agreement is not appropriate, and to collect information for a meaningful portion of the DIT, many agreements may need to be arranged.3. Object What is desired is to have an information server (or network of information servers) that can quickly respond to real world requests, like: - What is Tim Howes's email address? This is much harder than; What email address does Tim Howes at Netscape have ? - What is the X.509 certificate for Fred Smith at compuserve.com? One certainly doesn't want to search CompuServe's entire directory tree to find out this one piece of information. I also don't want to have to shadow the entire CompuServe directory subtree onto my server. If this request is being made because Fred is trying to log into my server, I'd certainly want to be able to respond to the BIND in real time. - Who are all the people at Novell that have a title of programmer? all these requests can reasonably be translated into LDAP or Whois++, and other directory access protocol queries. They can also be serviced in a straightforward way by the users home information server if it has the appropriate reference information into the database that contains the source data. Here, the first server would be able to "chain" the request for the user. Alternatively, a precise referral could be returned. If the home information server wants to service (i.e chain) the request based on the indexHedberg, et al. Experimental [Page 4] RFC 2654 Tagged Index Object for use in CIP August 1999 information that it has on hand, this servicing could be done several different means: - issuing LDAP operations to the remote directory server - issuing DSP operations to the remote directory server - issuing DAP operations to the remote directory server - issuing Whois++ operations to the remote Whois++ server - ...4. The Tagged Index Object This section defines a Tagged Index Object that can be exchanged by Information Servers using CIP. While often it is acceptable for Information Servers to make use of the Centroid definition (from [2]) to exchange index information, the goals in defining a new construct are multi-pronged: - When the Information Server receives a search request that warrants that a referral be returned, allow the server to return a referral that will point client to a server that is most likely able to answer the request correctly. False positive referrals (the search turns up hits in the index object that generate referrals to servers that don't hold the desired information) can be reduced, depending on the choice of attribute tokenization types that are used. - Potentially allow incremental updates that will then consume substantially less bandwidth then if full updates always had to be used.4.1. The Agreement Before a Tagged Index Object can be exchanged, the organization that administers the object supplier and the organization that administers the object consumer must reach an agreement on how the servers will communicate. This agreement contains the following: - "index-type": This specification describes the index type "x- tagged-index-1" - "dsi": An OID that uniquely identifies the subtree and scope. This field is not explicitly necessary, as it may not provide information beyond what is contained in the "base-uri" below.Hedberg, et al. Experimental [Page 5] RFC 2654 Tagged Index Object for use in CIP August 1999 - "base-uri": One or more URI's that will form the base of any referrals created based on the index object that is governed by this agreement. For example, in the LDAP URL format [8] the base-uri would specify (among other items): the LDAP host, the base object to which this index object refers (e.g. c=SE), and the scope of the index object (e.g. single container). - "supplier": The hostname and listening portnumber of the supplier server, as well as any alternative servers holding that same naming contexts, if the supplier is unavailable. - "consumeraddr": This is a URI of the "mailto:" form, with the RFC 822 email address of the consumer server. Further versions of this draft allow other forms of URI, so that the consumer may retrieve the update via the WWW, FTP or CIP. - "updateinterval": The maximum duration in seconds between occurances of the supplier server generating an update. If the consumer server has not received an update from the supplier server after waiting this long since the previous update, it is likely that the index information is now out of date. A typical value for a server with frequent updates would be 604800 seconds, or every week. Servers whose DITs are only modified annually could have a much longer update interval. - "attributeNamespace": Every set of index servers that together wants to support a specific usage of indeces, has to agree on which attributenames to use in the index objects. The participating directory servers also has to agree on the mapping from local attributenames to the attributenames used in the index. Since one specific index server might be involved in several such sets, it has to have some way to connect a update to the proper set of indexes. One possible solution to this would be to use different DSIs. - "consistencybase": How consistency of the index is maintained over incremental updates: "complete" - every change or delete concerning one object has to contain all tokens connected to that object. This method must be supported by any server who wants to comply with this standard. "tag" - starting at a full update every incremental update refering back to this full updated has to maintain state- information regarding tags, such that a object within the original database is assigned the same tagnumber every time. This method is optional.⌨️ 快捷键说明
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