| Rfc | 2258 |
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| Title | Internet Nomenclator Project |
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| Author | J. Ordille |
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| Date | January 1998 |
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| Format: | TXT, HTML |
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| Status: | INFORMATIONAL |
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|
Network Working Group J. Ordille
Request for Comments: 2258 Bell Labs, Lucent Technologies
Category: Informational January 1998
Internet Nomenclator Project
Status of this Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (1998). All Rights Reserved.
Abstract
The goal of the Internet Nomenclator Project is to integrate the
hundreds of publicly available CCSO servers from around the world.
Each CCSO server has a database schema that is tailored to the needs
of the organization that owns it. The project is integrating the
different database schema into one query service. The Internet
Nomenclator Project will provide fast cross-server searches for
locating people on the Internet. It augments existing CCSO services
by supplying schema integration, more extensive indexing, and two
kinds of caching -- all this in a system that scales as the number of
CCSO servers grows. One of the best things about the system is that
administrators can incorporate their CCSO servers into Nomenclator
without changing the servers. All Nomenclator needs is basic
information about the server.
This document provides an overview of the Nomenclator system,
describes how to register a CCSO server in the Internet Nomenclator
Project, and how to use the Nomenclator search engine to find people
on the Internet.
1. Introduction
Hundreds of organizations provide directory information through the
CCSO name service protocol [3]. Although the organizations provide a
wealth of information about people, finding any one person can be
difficult because each organization's server is independent. The
different servers have different database schemas (attribute names
and data formats). The 300+ CCSO servers have more than 900
different attributes to describe information about people. Very few
common attributes exist. Only name and email occur in more than 90%
of the servers [4]. No special support exists for cross-server
searches, so searching can be slow and expensive.
The goal of the Internet Nomenclator Project is to provide fast,
integrated access to the information in the CCSO servers. The
project is the first large-scale use of the Nomenclator system.
Nomenclator is a more general system than a white pages directory
service. It is a scalable, extensible information system for the
Internet.
Nomenclator answers descriptive (i.e. relational) queries. Users can
locate information about people, organizations, hosts, services,
publications, and other objects by describing their attributes.
Nomenclator achieves fast descriptive query processing through an
active catalog, and extensive meta-data and data caching. The active
catalog constrains the search space for a query by returning a list
of data repositories where the answer to the query is likely to be
found. Meta-data and data caching keep frequently used query
processing resources close to the user, thus reducing communication
and processing costs.
Through the Internet Nomenclator Project, users can query any CCSO
server, regardless of its attribute names or data formats, by
specifying the query to Nomenclator (see Figure 1). Nomenclator
provides a world view of the data in the different servers. Users
express their queries in this world view. Nomenclator returns the
answer immediately if it has been cached by a previous query. If not,
Nomenclator uses its active catalog to constrain the query to the
subset of relevant CCSO servers. The speed of the query is
increased, because only relevant servers are contacted. Nomenclator
translates the global query into local queries for each relevant CCSO
server. It then translates the responses into the format of the
world view.
--------------------------------------------------------------------
+-------------+ +-------------+
| | | |
World View | | Local View | |
Query | | Query | Relevant |
----------->| |------------>| |
| Nomenclator | | CCSO |
| | | |
<-----------| |<------------| Server |
World View | | Local View | |
Response | | Response | |
+-------------+ +-------------+
Figure 1: A Nomenclator Query
Nomenclator translates queries to and from
the language of the relevant CCSO servers.
--------------------------------------------------------------------
The Internet Nomenclator Project makes it easier for users to find a
particular CCSO server, but it does not send all queries to that
server. When Nomenclator constrains the search for a query answer,
it screens out irrelevant queries from ever reaching the server.
When Nomenclator finds an answer in its cache, it screens out
redundant queries from reaching the server. The server becomes
easier to find and use without experiencing the high loads caused by
exhaustive and redundant searches.
The Internet Nomenclator Project creates the foundation for a much
broader heterogeneous directory service for the Internet. The
current version of Nomenclator provides integrated access to CCSO and
relational database services. The Nomenclator System Architecture
supports fast, integrated searches of any collection of heterogeneous
directories. The Internet Nomenclator Project can be enhanced to
support additional name services, or provide intergated query
services for other application domains. The project is starting with
CCSO services, because the CCSO services are widely available and
successful.
Section 2 describes the Nomenclator system in more detail. Section 3
explains how to register a CCSO server as part of the project.
Section 4 briefly describes how to use Nomenclator. Section 5
provides a summary.
2. Nomenclator System
Nomenclator is a scalable, extensible information system for the
Internet. It supports descriptive (i.e. relational) queries. Users
locate information about people, organizations, hosts, services,
publications, and other objects by describing their attributes.
Nomenclator achieves fast descriptive query processing through an
active catalog, and extensive meta-data and data caching.
The active catalog constrains the search space for a query by
returning a list of data repositories where the answer to the query
is likely to be found. Components of the catalog are distributed
indices that isolate queries to parts of the network, and smart
algorithms for limiting the search space by using semantic,
syntactic, or structural constraints. Meta-data caching improves
performance by keeping frequently used characterizations of the
search space close to the user, thus reducing active catalog
communication and processing costs. When searching for query
responses, these techniques improve query performance by contacting
only the data repositories likely to have actual responses, resulting
in acceptable search times.
Administrators make their data available in Nomenclator by supplying
information about the location, format, contents, and protocols of
their data repositories. Experience with Nomenclator shows that
gathering a small amount of information from data owners can have a
substantial positive impact on the ability of users to retrieve
information. For example, each CCSO administrator provides a mapping
from the local view of data (i.e. the local schema) at the CCSO
server to Nomenclator's world view. The administrator also supplies
possible values for any attributes with small domains at the data
repository (such as the "city" or "state_or_province" attributes).
With this information, Nomenclator can isolate queries to a small
percentage of the CCSO data repositories, and provide an integrated
view of their data. Nomenclator provides tools that minimize the
effort that administrators expend in characterizing their data
repositories. Nomenclator does not require administrators to change
the format of their data or the access protocol for their database.
2.1 Components of a Nomenclator System
A Nomenclator system is comprised of a distributed catalog service
and a query resolver (see Figure 2). The distributed catalog service
gathers meta-data about data repositories and makes it available to
the query resolver. Meta-data includes constraints on attribute
values at a data repository, known patterns of data distribution
across several data repositories, search and navigation techniques,
schema and protocol translation techniques, and the differing schema
at data repositories.
--------------------------------------------------------------------
+-------------+ +-------------+
| | | |
World View | | Meta Data | |
Query | | Request | Distributed |
----------->| Query | ----------->| |
| Resolver | | Catalog |
| | | |
<-----------| (caches) | <-----------| Service |
World View | | Meta Data | |
Response | | Response | |
+-------------+ +-------------+
Figure 2: Components of a Nomenclator System
--------------------------------------------------------------------
Query resolvers at the user sites retrieve, use, cache, and re-use
this meta-data in answering user queries. The catalog is "active" in
two ways. First, some meta-data moves from the distributed catalog
service to each query resolver during query processing. Second, the
query resolver uses the initial meta-data, in particular the search
and navigation techniques, to generate additional meta-data that
guides query processing. Typically, one resolver process serves a
few hundred users in an organization, so users can benefit from
larger resolver caches.
Query resolvers cache techniques for constraining the search space
and the results of previously constrained searches (meta-data), and
past query answers (data) to speed future query processing. Meta-
data and data caching tailor the query resolver to the specific needs
of the users at the query site. They also increase the scale of a
Nomenclator system by reducing the load from repeated searches or
queries on the distributed catalog service, data repositories, and
communications network.
The distributed catalog service is logically one network service, but
it can be divided into pieces that are distributed and/or replicated.
Query resolvers access this distributed, replicated service using the
same techniques that work for multiple data repositories.
A Nomenclator system naturally includes many query resolvers.
Resolvers are independent, but renewable, query agents that can be as
powerful as the resources available at the user site. Caching
decreases the dependence of the resolver on the distributed catalog
service for frequently used meta-data, and on data repositories for
frequently used data. Caching thus improves the number of users that
can be supported and the local availability of the query service.
2.2 Meta-Data Techniques
The active catalog structures the information space into a collection
of relations about people, hosts, organizations, services and other
objects. It collects meta-data for each relation and structures it
into "access functions" for locating and retrieving data. Access
functions respond to the question: "Where is data to answer this
query?" There are two types of responses corresponding to the two
types of access functions. The first type of response is: "Look over
there." "Catalog functions" return this response; they constrain the
query search by limiting the data repositories contacted to those
having data relevant to the query. Catalog functions return a
referral to data access functions that will answer the query or to
additional catalog functions to contact for more detailed
information. The second response to "Where?" is: "Here it is!" "Data
access functions" return this response; they understand how to obtain
query answers from specific data repositories. They return tuples
that answer the query. Nomenclator supplies access functions for
common name services, such as the CCSO service, and organizations can
write and supply access functions for data in their repositories.
Access functions are implemented as remote or local services. Remote
access functions are services that are available through a standard
remote procedure call interface. Local access functions are
functions that are supplied with the query resolver. Local access
functions can be applied to a variety of indexing and data retrieval
tasks by loading them with meta-data stored in distributed catalog
service. Remote access functions are preferred over local ones when
the resources of the query resolver are inadequate to support the
access function. The owners of data may also choose to supply remote
access functions for privacy reasons if their access functions use
proprietary information or algorithms. Local functions are preferred
whenever possible, because they are highly replicated in resolver
caches. They can reduce system and network load by bringing the
resources of the active catalog directly to the users.
Remote access functions are simple to add to Nomenclator and local
access functions are simple to apply to new data repositories,
because the active catalog provides "referrals" that describe the
conditions for using access functions. For simplicity, this document
describes referral techniques for exact matching of query strings.
Extensions to these techniques in Nomenclator support matching query
strings that contain wildcards or word-based matching of query
strings in the style of the CCSO services.
Each referral contains a template and a list of references to access
functions. The template is a conjunctive selection predicate that
describes the scope of the access functions. Conjunctive queries
that are within the scope of the template can be answered with the
referral. When a template contains a wildcard value ("*") for an
attribute, the attribute must be present in any queries that are
processed by the referral. The system follows the following rule:
Query Coverage Rule:
If the set of tuples satisfying the selection predicate in a query
is covered by (is a subset of) the set of tuples satisfying the
template, then the query can be answered by the access functions in
the reference list of the referral.
For example, the query below:
select * from People where country = "US" and surname = "Ordille";
is covered by the following templates in Lines (1) through (3), but
not by the templates in Lines (4) and (5):
(1) country = "US" and surname = "*"
(2) country = "US" and surname = "Ordille"
(3) country = "US"
(4) organization = "*"
(5) country = "US" and surname = "Elliott"
Referrals form a generalization/specialization graph for a relation
called a "referral graph." Referral graphs are a conceptual tool
that guides the integration of different catalog functions into our
system and that supplies a basis for catalog function construction
and query processing. A "referral graph" is a partial ordering of
the referrals for a relation. It is constructed using the
subset/superset relationship: "S is a subset of G." A referral S is
a subset of referral G if the set of queries covered by the template
of S is a subset of the set of queries covered by the template of G.
S is considered a more specific referral than G; G is considered a
more general referral than S. For example, the subset relationship
exists between the pairs of referrals with the templates listed
below:
(1) country = "US" and surname = "Ordille"
is a subset of
country = "US"
(2) country = "US" and surname = "Ordille"
is a subset of
country = "US" and surname = "*"
(3) country = "US" and surname = "*"
is a subset of
country ="US"
(4) country = "US"
is a subset
"empty template"
but it does not exist between the pairs of referrals with the
following templates:
(5) country = "US"
is not a subset of
department = "CS"
(6) country = "US" and name = "Ordille"
is not a subset of
country = "US" and name = "Elliott"
In Lines (1) and (2), the more general referral covers more queries,
because it covers queries that list different values for surname. In
Line (3), the more general referral covers more queries, because it
covers queries that do not constrain surname to a value. In Line
(4), the specific referral covers only those queries that constrain
the country to "US" while the empty template covers all queries.
During query processing, wildcards in a template are replaced with
the value of the corresponding attribute in the query. For any query
covered by two referrals S and G such that S is a subset of G, the
set of tuples satisfying the template in S is covered by the set of
tuples satisfying the template in G. S is used to process the query,
because it provides the more constrained (and faster) search space.
The referral S has a more constrained logical search space than G,
because the set of tuples in the scope of S is no larger, and often
smaller, than the set in the scope of G. Moreover, S has a more
constrained physical search space than G, because the data
repositories that must contacted for answers to S must also be
contacted for answers to G, but additional data repositories may need
to be contacted to answer G.
In constraining a query, a catalog function always produces a
referral that is more specific than the referral containing the
catalog function. Wildcards ("*") in a template indicate which
attribute values are used by the associated catalog function to
generate a more specific referral. In other words, catalog functions
always follow the rule:
Catalog Function Constrained Search Rule:
Given a referral R with a template t and a catalog function cf,
and a query q covered by t, the result of using cf to process q,
cf(q), is a referral R' with template t' such that q is covered
by t' and R' is more specific than R.
Catalog functions make it possible to import a portion of the indices
for the information space into the query resolver. Since they
generate referrals, the resolver can cache the most useful referrals
for a relation and call the catalog function as needed to generate
new referrals.
The resolver query processing algorithm obtains an initial set of
referrals from the distributed catalog service. It then navigates
the referral graph, calling catalog functions as necessary to obtain
additional referrals that narrow the search space. Sometimes, two
referrals that cover the query have the relationship of general to
specific to each other. The resolver eliminates unnecessary access
function processing by using only the most specific referral along
each path of the referral graph.
The search space for the query is initially set to all the data
repositories in the relation. As the resolver obtains referrals to
sets of relevant data repositories (and their associated data access
functions) it forms the intersection of the referrals to constrain
the search space further. The intersection of the referrals includes
only those data repositories listed in all the referrals.
Intersection combines independent paths through the referral graph to
derive benefit from indices on different attributes.
2.3 Meta-Data and Data Caching
A Nomenclator query resolver caches the meta-data that result from
calling catalog functions. It also caches the responses for queries.
If the predicate of a new query is covered by the predicate of a
previous query, Nomenclator calculates the response for the new query
from the cached response of the old query. Nomenclator timestamps
its cache entries to provide measures of the currentness of query
responses and selective cache refresh. The timestamps are used to
calculate a t-bound on query responses [5][1]. A t-bound is the time
after which changes may have occurred to the data that are not
reflected in the query response. It is the time of the oldest cache
entry used to calculate the response. Nomenclator returns a t-bound
with each query response. Users can request more current data by
asking for responses that are more recent than this t-bound. Making
such a request flushes older items from the cache if more recent
items are available. Query resolvers calculate a minimum t-bound
that is some refresh interval earlier than the current time.
Resolvers keep themselves current by replacing items in the cache
that are earlier than the minimum t-bound.
2.4 Scale and Performance
Three performance studies of active catalog and meta-data caching
techniques are available [5]. The first study shows that the active
catalog and meta-data caching can constrain the search effectively in
a real environment, the X.500 name space. The second study examined
the performance of an active catalog and meta-data caching for single
users on a local area network. The experiments showed that the
techniques to eliminate data repositories from the search space can
dramatically improve response time. Response times improve, because
latency is reduced. The reduction of latency in communications and
processing is critical to large-scale descriptive query optimization.
The experiments also showed that an active catalog is the most
significant contributor to better response time in a system with low
load, and that meta-data caching functions to reduce the load on the
system. The third study used an analytical model to evaluate the
performance and scaling of these techniques for a large Internet
environment. It showed that meta-data caching plays an essential
role in scaling the distributed catalog service to millions of users.
It also showed that constraining the search space with an active
catalog contributes significantly to scaling data repositories to
millions of users. Replication and data caching also contribute to
the scale of the system in a large Internet environment.
3. Registering a CCSO Server
The Internet Nomenclator Project supports the following home page:
http://cm.bell-labs.com/cs/what/nomenclator
The home page provides a variety of information and services.
Administrators can register their CCSO servers through services on
this home page. The registration service collects CCSO server
location information, contact information for the administrator of
the CCSO server, implicit and explicit constraints on entries in the
server's database, and a mapping from the local schema of the CCSO
server to the schema of the world view.
The implicit and explicit constraints on the server's database are
the fuel for Nomenclator's catalog functions. The registration
center currently collects constraints on organization name,
department, city, state or province name, country, phone number,
postal code, and email address. These constraints are automatically
incorporated into Nomenclator's distributed catalog service. They
are used by catalog functions in query resolvers to constrain
searches to relevant CCSO servers. For example, a database only
contains information about the computer science and electrical
engineering departments at a French university. The department,
organization and country attributes are constrained. Nomenclator
uses these constraints to prevent queries about other departments,
organizations or countries from being sent to this CCSO server.
The mapping from the local schema of the CCSO server to the schema of
the world view allows Nomenclator to translate queries and responses
for the CCSO server. The registration center currently collects this
mapping by requesting an example of how to translate a typical entry
in the CCSO server into the world view schema and, optionally, an
example of how to translate a canonical entry in the world view
schema into the local schema of the CCSO server [4]. These examples
are then used to generate a mapping program that is stored in the
distributed catalog service. The CCSO data access function in the
query resolver interprets these programs to translate queries and
responses communicated with that CCSO server. We plan to release the
mapping language to CCSO server administrators, so administrators can
write and maintain the mapping for their servers. We have
experimented with more than 20 mapping programs. They are seldom
more than 50 lines, and are often shorter. It typically takes one or
two lines to map an attribute.
4. Using Nomenclator
The Internet Nomenclator Project currently provides a centralized
query service on the Internet. The project runs a Nomenclator query
resolver that is accessible through its Web page (see the URL in
Section 3) and the Simple Nomenclator Query Protocol (SNQP) [2].
The service answers queries that are a conjunction of string values
for attributes. A variety of matching techniques are supported
including exact string matching, matching with wildcards, and word-
based matching in the style of the CCSO service. Our web interface
uses the Simple Nomenclator Query Protocol (SNQP) [2]. Programmers
can create their own interfaces by using this protocol to communicate
with the Nomenclator query resolver. They will require the host name
and port number for the query resolver which they can obtain from the
Nomenclator home page. SNQP, and hence the web interface, are
defined for US-ASCII. Support for other character sets will require
further work.
Subsequent phases of the project will provide enhanced services such
as providing advice about the cost of queries and ways to constrain
queries further to produce faster response times, and allowing users
to request more current data. We also plan to distribute query
resolvers, so users can benefit from running query resolvers locally.
Local query resolvers reduce latency for the user, and distribute
query processing load throughout the network.
5. Summary
The Internet Nomenclator Project augments existing CCSO services by
supplying schema integration and fast cross-server searches. The key
to speed in descriptive query processing is an active catalog, and
extensive meta-data and data caching. The Nomenclator system is the
result of research in distributed systems [5][6][7][4]. It can be
extended to incorporate other name servers, besides the CCSO servers,
and to address distributed search and retrieval challenges in other
application domains. In addition to providing a white pages service,
the Internet Nomenclator Project will evaluate how an active catalog,
meta-data caching and data caching perform in very large global
information system. The ultimate goal of the project is to refine
these techniques to provide the best possible global information
systems.
6. Security Considerations
In the Internet Nomenclator Project, the participants' data are
openly available and read-only. Since the risk of tampering with
queries and responses is considered low, this version of Nomenclator
does not define procedures for protecting the information in its
queries and responses.
7. References
[1] H. Garcia-Molina, G. Wiederhold. "Read-Only Transactions in
a Distributed Database," ACM Transactions on Database Systems
7(2), pp. 209-234. June 1982.
[2] Elliott, J., and J. Ordille, "The Simple Nomenclator Query
Protocol (SNQP)," RFC 2259, January 1998.
[3] S. Dorner, P. Pomes. "The CCSO Nameserver: A Description,"
Computer and Communications Services Office Technical Report,
University of Illinois, Urbana, USA. 1992. Avaialble in the
current "qi" distribution from
<URL:ftp://uiarchive.cso.uiuc.edu/local/packages/ph>
[4] A. Levy, J. Ordille. "An Experiment in Integrating Internet
Information Sources," AAAI Fall Symposium on AI Applications in
Knowledge Navigation and Retrieval, November 1995.
<URL:http://cm.bell-labs.com/cm/cs/doc/95/11-01.ps.gz>
[5] J. Ordille. "Descriptive Name Services for Large Internets,"
Ph. D. Dissertation. University of Wisconsin. 1993.
<URL:http://cm.bell-labs.com/cm/cs/doc/93/12-01.ps.gz>
[6] J. Ordille, B. Miller. "Distributed Active Catalogs and
Meta-Data Caching in Descriptive Name Services," Thirteenth
International IEEE Conference on Distributed Computing Systems,
pp. 120-129. May 1993.
<URL:http://cm.bell-labs.com/cm/cs/doc/93/5-01.ps.gz>
[7] J. Ordille, B. Miller. "Nomenclator Descriptive Query
Optimization in Large X.500 Environments," ACM SIGCOMM
Symposium on Communications Architectures and Protocols, pp.
185-196, September 1991.
<URL:http://cm.bell-labs.com/cm/cs/doc/91/9-01.ps.gz>
8. Author's Address
Joann J. Ordille
Bell Labs, Lucent Technologies
Computing Sciences Research Center
700 Mountain Avenue, Rm 2C-301
Murray Hill, NJ 07974 USA
EMail: joann@bell-labs.com
9. Full Copyright Statement
Copyright (C) The Internet Society (1998). All Rights Reserved.
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