| Rfc | 1913 |
|---|
| Title | Architecture of the Whois++ Index Service |
|---|
| Author | C. Weider, J. Fullton, S.
Spero |
|---|
| Date | February 1996 |
|---|
| Format: | TXT, HTML |
|---|
| Status: | HISTORIC |
|---|
|
Network Working Group C. Weider
Request for Comments: 1913 Bunyip
Category: Standards Track J. Fullton
CNIDR
S. Spero
EIT
February 1996
Architecture of the Whois++ Index Service
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Abstract
The authors describe an architecture for indexing in distributed
databases, and apply this to the WHOIS++ protocol.
1. Purpose:
The WHOIS++ directory service [Deutsch, et al, 1995] is intended to
provide a simple, extensible directory service predicated on a
template-based information model and a flexible query language. This
document describes a general architecture designed for indexing
distributed databases, and then applys that architecture to link
together many of these WHOIS++ servers into a distributed, searchable
wide area directory service.
2. Scope:
This document details a distributed, easily maintained architecture
for providing a unified index to a large number of distributed
WHOIS++ servers. This architecture can be used with systems other
than WHOIS++ to provide a distributed directory service which is also
searchable.
3. Motivation and Introduction:
It seems clear that with the vast amount of directory information
potentially available on the Internet, it is simply not feasible to
build a centralized directory to serve all this information. If we
are to distribute the directory service, the easiest (although not
necessarily the best) way of building the directory service is to
build a hierarchy of directory information collection agents. In this
architecture, a directory query is delivered to a certain agent in
the tree, and then handed up or down, as appropriate, so that the
query is delivered to the agent which holds the information which
fills the query. This approach has been tried before, most notably
in some implementations of the X.500 standard. However, there are
number of major flaws with the approach as it has been taken. This
new Index Service is designed to fix these flaws.
3.1. The search problem
One of the primary assumptions made by recent implementations of
distributed directory services is that every entry resides in some
location in a hierarchical name space. While this arrangement is
ideal for reading the entry once one knows its location, it is not as
good when one is searching for the location in the namespace of those
entries which meet some set of criteria. If the only criteria we know
about a desired entry are items which do not appear in the namespace,
we are forced to do a global query. Whenever we issue a global query
(at the root of the namespace), or a query at the top of a given
subtree in the namespace, that query is replicated to "all" subtrees
of the starting point. The replication of the query to all subtrees
is not necessarily a problem; queries are cheap. However, every
server to which the query has been replicated must process that
query, even if it has no entries which match the specified criteria.
This part of the global query processing is quite expensive. A poorly
designed namespace or a thin namespace can cause the vast majority of
queries to be replicated globally, but a very broad namespace can
cause its own navigation problems. Because of these problems, search
has been turned off at high levels of the X.500 namespace.
3.2. The location problem
With global search turned off, one must know in advance how the name
space is laid out so that one can guide a query to a proper location.
Also, the layout of the namespace then becomes critical to a user's
ability to find the desired information. Thus there are endless
battles about how to lay out the name space to best serve a given set
of users, and enormous headaches whenever it becomes apparent that
the current namespace is unsuited to the current usages and must be
changed (as recently happened in X.500). Also, assuming one does
impose multiple hierarchies on the entries through use of the
namespace, the mechanisms to maintain these multiple hierarchies in
X.500 do not exist yet, and it is possible to move entries out from
under their pointers. Also, there is as yet no agreement on how the
X.500 namespace should look even for the White Pages types of
information that is currently installed in the X.500 pilot project.
3.3. The Yellow Pages problem
Current implementations of this hierarchical architecture have also
been unsuited to solving the Yellow Pages problem; that is, the
problem of easily and flexibly building special-purpose directories
(say of molecular biologists) and of automatically maintaining these
directories once they have been built. In particular, the attributes
appropriate to the new directory must be built into the namespace
because that is the only way to segregate related entries into a
place where they can be found without a global search. Also, there is
a classification problem; how does one adequately specify the proper
categories so that people other than the creator of the directory can
find the correct subtree? Additionally, there is the problem of
actually finding the data to put into the subtree; if one must
traverse the hierarchy to find the data, we have to look globally for
the proper entries.
3.4. Solutions
The problems examined in this section can be addressed by a
combination of two new techniques: directory meshes and forward
knowledge.
4. Directory meshes and forward knowledge
We'll hold off for a moment on describing the actual architecture
used in our solution to these problems and concentrate on a high
level description of what solutions are provided by our conceptual
approach. To begin with, although every entry in WHOIS++ does indeed
have a unique identifier (resides in a specific location in the
namespace) the navigational algorithms to reach a specific entry do
not necessarily depend on the identifier the entry has been assigned.
The Index Service gets around the namespace and hierarchy problems by
creating a directory mesh on top of the entries. Each layer of the
mesh has a set of 'forward knowledge' which indicates the contents of
the various servers at the next lower layer of the mesh. Thus when a
query is received by a server in a given layer of the mesh, it can
prune the search tree and hand the query off to only those lower
level servers which have indicated that they might be able to answer
it. Thus search becomes feasible at all levels of the mesh. In the
current version of this architecture, we have chosen a certain set of
information to hand up the mesh as forward knowledge. This may or may
not be exactly the set of information required to construct a truly
searchable directory, but the protocol itself doesn't restrict the
types of information which can be handed around.
In addition, the protocols designed to maintain the forward knowledge
will also work perfectly well to provide replication of servers for
redundancy and robustness. In this case, the forward knowledge handed
around by the protocols is the entire database of entries held by the
replicated server.
Another benefit provided by the mesh of index servers is that since
the entry identification scheme has been decoupled from the
navigation service, multiple hierarchies can be built and easily
maintained on top of the existing data. Also, the user does not need
to know in advance where in the mesh the entry is contained.
Also, the Yellow Pages problem now becomes tractable, as the index
servers can pick and choose between information proffered by a given
server; because we have an architecture that allows for automatic
polling of data, special purpose directories become easy to construct
and to maintain.
5. Components of the Index Service:
5.1. WHOIS++ servers
The whois++ service is described in [Deutsch, et al, 1995]. As that
service specifies only the query language, the information model, and
the server responses, whois++ services can be provided by a wide
variety of databases and directory services. However, to participate
in the Index Service, that underlying database must also be able to
generate a 'centroid', or some other type of forward knowledge, for
the data it serves.
5.2. Centroids as forward knowledge
The centroid of a server is comprised of a list of the templates and
attributes used by that server, and a word list for each attribute.
The word list for a given attribute contains one occurrence of every
word which appears at least once in that attribute in some record in
that server's data, and nothing else.
A word is any token delimited by blank spaces, newlines, or the '@'
character, in the value of an attribute.
For example, if a whois++ server contains exactly three records, as
follows:
Record 1 Record 2
Template: User Template: User
First Name: John First Name: Joe
Last Name: Smith Last Name: Smith
Favourite Drink: Labatt Beer Favourite Drink: Molson Beer
Record 3
Template: Domain
Domain Name: foo.edu
Contact Name: Mike Foobar
the centroid for this server would be
Template: User
First Name: Joe
John
Last Name: Smith
Favourite Drink: Beer
Labatt
Molson
Template: Domain
Domain Name: foo.edu
Contact Name: Mike
Foobar
It is this information which is handed up the tree to provide forward
knowledge. As we mention above, this may not turn out to be the
ideal solution for forward knowledge, and we suspect that there may
be a number of different sets of forward knowledge used in the Index
Service. However, the directory architecture is in a very real sense
independent of what types of forward knowledge are handed around, and
it is entirely possible to build a unified directory which uses many
types of forward knowledge.
5.3. Index servers and Index server Architecture
A whois++ index server collects and collates the centroids (or other
forward knowledge) of either a number of whois++ servers or of a
number of other index servers. An index server must be able to
generate a centroid for the information it contains. In addition, an
index server can index any other server it wishes, which allows one
base level server (or index server) to participate in many
hierarchies in the directory mesh.
5.3.1. Queries to index servers
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 then
notifies the user's client of the next servers to contact to submit
the query (referral in the X.500 model). An index server can also
contain primary data of its own; and thus act a both an index server
and a base level server. In this case, the index server's response to
a query may be a mix of records and referral pointers.
5.3.2. Index server distribution model and centroid propogation
The diagram on the next page illustrates how a mesh of index servers
might be created for a set of whois++ servers. Although it looks like
a hierarchy, the protocols allow (for example) server A to be indexed
by both server D and by server H.
whois++ index index
servers servers servers
for for
whois++ lower-level
servers index servers
_______
| |
| A |__
|_______| \ _______
\----------| |
_______ | D |__ ______
| | /----------|_______| \ | |
| B |__/ \----------| |
|_______| | F |
/----------|______|
/
_______ _______ /
| | | |-
| C |--------------| E |
|_______| |_______|-
\
\
_______ \ ______
| | \----------| |
| G |--------------------------------------| H |
|_______| |______|
Figure 1: Sample layout of the Index Service mesh
In the portion of the index tree shown above, whois++ servers A and B
hand their centroids up to index server D, whois++ server C hands its
centroid up to index server E, and index servers D and E hand their
centroids up to index server F. Servers E and G also hand their
centroids up to H.
The number of levels of index servers, and the number of index
servers at each level, will depend on the number of whois++ servers
deployed, and the response time of individual layers of the server
tree. These numbers will have to be determined in the field.
5.3.3. Centroid propogation and changes to centroids
Centroid propogation is initiated by an authenticated POLL command
(sec. 5.2). The format of the POLL command allows the poller to
request the centroid of any or all templates and attributes held by
the polled server. After the polled server has authenticated the
poller, it determines which of the requested centroids the poller is
allowed to request, and then issues a CENTROID-CHANGES report (sec.
5.3) to transmit the data. When the poller receives the CENTROID-
CHANGES report, it can authenticate the pollee to determine whether
to add the centroid changes to its data. Additionally, if a given
pollee knows what pollers hold centroids from the pollee, it can
signal to those pollers the fact that its centroid has changed by
issuing a DATA-CHANGED command. The poller can then determine if and
when to issue a new POLL request to get the updated information. The
DATA-CHANGED command is included in this protocol to allow
'interactive' updating of critical information.
5.3.4. Centroid propogation and mesh traversal
When an index server issues a POLL request, it may indicate to the
polled server what relationship it has to the polled. This
information can be used to help traverse the directory mesh. Two
fields are specified in the current proposal to transmit the
relationship information, although it is expected that richer
relationship information will be shared in future revisions of this
protocol.
One field used for this information is the Hierarchy field, and can
take on three values. The first is 'topology', which indicates that
the indexing server is at a higher level in the network topology
(e.g. indexes the whole regional ISP). The second is 'geographical',
which indicates that the polling server covers a geographical area
subsuming the pollee. The third is 'administrative', which indicates
that the indexing server covers an administrative domain subsuming
the pollee.
The second field used for this information is the Description field,
which contains the DESCRIBE record of the polling server. This allows
users to obtain richer metainformation for the directory mesh,
enabling them to expand queries more effectively.
5.3.5. Query handling and passing algorithms
When an index server receives a query, it searches its collection of
centroids and determines which servers hold records which may fill
that query. As whois++ becomes widely deployed, it is expected that
some index servers may specialize in indexing certain whois++
templates or perhaps even certain fields within those templates. If
an index server obtains a match with the query "for those template
fields and attributes the server indexes", it is to be considered a
match for the purpose of forwarding the query.
5.3.5.1. Query referral
Query referral is the process of informing a client which servers to
contact next to resolve a query. The syntax for notifying a client
is outlined in section 5.5.
5.3.6 Loop control
Since there are no a priori restrictions on which servers may poll
which other servers, and since a given server may participate in many
sub-meshes, mechanisms must be installed to allow the detection of
cycles in the polling relationships. This is accomplished in the
current protocol by including a hop-count on polling relationships.
Each time a polled server generates forward information, it informs
the polling server about its current hopcount, which is the maximum
of the hopcounts of all the servers it polls, plus 1. A base level
server (one which polls no other servers) will have a hopcount of 0.
When a server decides to poll a new server, if its hopcount goes up,
then it must information all the other servers which poll it about
its new hopcount. A maximum hopcount (8 in the current version) will
help the servers detect polling loops.
A second approach to loop detection is to do all the work in the
client; which would determine which new referrals have already
appeared in the referral list, and then simply iterate the referral
process until there are no new servers to ask. An algorithm to
accomplish this in WHOIS++ is detailed in [Faltstrom 95].
6. Syntax for operations of the Index Service:
The syntax for each protocol componenet is listed below. In addition,
each section contains a listing of which of these attributes is
required and optional for each of the componenet. All timestamps must
be in the format YYYYMMDDHHMM and in GMT.
6.1. Data changed syntax
The data changed template look like this:
# DATA-CHANGED
Version-number: // version number of index service software, used to
// insure compatibility. Current value is 1.0
Time-of-latest-centroid-change: // time stamp of latest centroid
// change, GMT
Time-of-message-generation: // time when this message was generated,
// GMT
Server-handle: // IANA unique identifier for this server
Host-Name: // Host name of this server (current name)
Host-Port: // Port number of this server (current port)
Best-time-to-poll: // For heavily used servers, this will identify
// when the server is likely to be lightly
// loaded so that response to the poll will be
//speedy, GMT
Authentication-type: // Type of authentication used by server, or NONE
Authentication-data: // data for authentication
# END // This line must be used to terminate the data changed
// message
Required/optional table
Version-Number REQUIRED
Time-of-latest-centroid-change REQUIRED
Time-of-message-generation REQUIRED
Server-handle REQUIRED
Host-Name REQUIRED
Host-Port REQUIRED
Best-time-to-poll OPTIONAL
Authentication-type OPTIONAL
Authentication-data OPTIONAL
6.2. Polling syntax
# POLL:
Version-number: // version number of poller's index software, used to
// insure compatibility
Type-of-poll: // type of forward data requested. CENTROID or QUERY
// are the only one currently defined
Poll-scope: // Selects bounds within which data will be returned.
// See note.
Start-time: // give me all the centroid changes starting at this
// time, GMT
End-time: // ending at this time, GMT
Template: // a standard whois++ template name, or the keyword ALL,
// for a full update.
Field: // used to limit centroid update information to specific
// fields, is either a specific field name, a list of field
// names, or the keyword ALL
Server-handle: // IANA unique identifier for the polling server.
// this handle may optionally be cached by the polled
// server to announce future changes
Host-Name: // Host name of the polling server.
Host-Port: // Port number of the polling server.
Hierarchy: // This field indicates the relationship which the poller
// bears to the pollee. Typical values might include
// 'Topology', 'Geographical", or "Administrative"
Description: // This field contains the DESCRIBE record of the
// polling server
Authentication-type: // Type of authentication used by poller, or NONE
Authentication-data: // Data for authentication
# END // This line must by used to terminate the poll message
Note: For poll type CENTROID, the allowable values for Poll Scope are
FULL and RELATIVE. Support of the FULL value is required, this
provides a complete listing of the centroid or other forward
information. RELATIVE indicates that these are the relative changes
in the centroid since the last report to the polling server.
For poll type QUERY, the allowable values for Poll Scope are a blank
line, which indicates that all records are to be returned, or a valid
WHOIS++ query, which indicates that just those records which satisfy
the query are to be returned. N.B. Security considerations may
require additional authentication for successful response to the
Blank Line Poll Scope. This value has been included for server
replication.
A polling server may wish to index different types of information
than the polled server has collected. The POLLED-FOR command will
indicate which servers the polled server has contacted.
Required/Optional Table
Version-Number REQUIRED, value is 1.0
Type-Of-Poll REQUIRED, values CENTROID and QUERY are required
Poll-scope REQUIRED If Type-of-poll is CENTROID, FULL is required,
RELATIVE is optional
If Type-of-poll is QUERY, Blank line is
required, and WHOIS++-type queries are
required
Start-time OPTIONAL
End-Time OPTIONAL
Template REQUIRED
Field REQUIRED
Server-handle REQUIRED
Host-Name REQUIRED
Host-Port REQUIRED
Hierarchy OPTIONAL
Description OPTIONAL
Authentication-Type: OPTIONAL
Authentication-data: OPTIONAL
Example of a POLL command:
# POLL:
Version-number: 1.0
Type-of-poll: CENTROID
Poll-scope: FULL
Start-time: 199501281030+0100
Template: ALL
Field: ALL
Server-handle: BUNYIP01
Host-Name: services.bunyip.com
Host-Port: 7070
Hierarchy: Geographical
# END
6.3. Centroid change report
As the centroid change report contains nested multiply-occuring
blocks, each multiply occurring block is surrounded *in this paper*
by curly braces '{', '}'. These curly braces are NOT part of the
syntax, they are for identification purposes only.
The syntax of a Data: item is either a list of words, one word per
line, or the keyword:
ANY
The keyword ANY as the only item of a Data: list means that any value
for this field should be treated as a hit by the indexing server.
The field Any-field: needs more explanation than can be given in the
body of the syntax description below. It can take two values, True or
False. If the value is True, the pollee is indicating that there are
fields in this template which are not being exported to the polling
server, but wishes to treat as a hit. Thus, when the polling server
gets a query which has a term requesting a field not in this list for
this template, the polling server will treat that term as a 'hit'.
If the value is False, the pollee is indicating that there are no
other fields for this template which should be treated as a hit. This
field is required because the basic model for the WHOIS++ query
syntax requires that the results of each search term be 'and'ed
together. This field allows polled servers to export data only for
non-sensitive fields, yet still get referrals of queries which
contain sensitive terms.
IMPORTANT: The data listed in the centroid must be in the ISO-8859-1
character set in this version of the indexing protocol. Use of any
other character set is a violation of the protocol. Note that the
base-level server is also specified to use ISO-8859-1 [Deutsch, et
al, 1995].
# CENTROID-CHANGES
Version-number: // version number of pollee's index software, used to
// insure compatibility
Start-time: // change list starting time, GMT
End-time: // change list ending time, GMT
Server-handle: // IANA unique identifier of the responding server
Case-sensitive: // states whether data is case sensitive or case
// insensitive. values are TRUE or FALSE
Authentication-type: // Type of authentication used by pollee, or NONE
Authentication-data: // Data for authentication
Compression-type: // Type of compression used on the data, or NONE
Size-of-compressed-data: // size of compressed data if compression
// is used
Operation: // One of 3 keywords: ADD, DELETE, FULL
// ADD - add these entries to the centroid for this server
// DELETE - delete these entries from the centroid of this
// server
// FULL - the full centroid as of end-time follows
{ // The multiply occurring template block starts here
# BEGIN TEMPLATE
Template: // a standard whois++ template name
Any-field: // TRUE or FALSE. See beginning of 6.3 for explanation.
{ // the template contains multiple field blocks
# BEGIN FIELD
Field: // a field name within that template
Data: // Either the keyword *ANY*, or
// the word list itself, one per line, cr/lf terminated,
// each line starting with a dash character ('-').
# END FIELD
} // the field ends with END FIELD
# END TEMPLATE
} // the template block ends with END TEMPLATE
# END CENTROID-CHANGES // This line must be used to terminate the
// centroid change report
For each template, all fields must be listed, or queries will not be
referred correctly.
Required/Optional table
Version-number REQUIRED, value is 1.0
Start-time REQUIRED (even if the centroid type is FULL)
End-time REQUIRED (even if the centroid type is FULL)
Server-handle REQUIRED
Case-Sensitive OPTIONAL
Authentication-Type OPTIONAL
Authentication-Data OPTIONAL
Compression-type OPTIONAL
Size-of-compressed-data OPTIONAL (even if compression is used)
Operation OPTIONAL, if used, upport for all three values is required
Tokenization-type OPTIONAL
#BEGIN TEMPLATE REQUIRED
Template REQUIRED
Any-field REQUIRED
#BEGIN FIELD REQUIRED
Field REQUIRED
Data REQUIRED
#END FIELD REQUIRED
#END TEMPLATE REQUIRED
#END CENTROID-CHANGES REQUIRED
Example:
# CENTROID-CHANGES
Version-number: 1.0
Start-time: 197001010000
End-time: 199503012336
Server-handle: BUNYIP01
# BEGIN TEMPLATE
Template: USER
Any-field: TRUE
# BEGIN FIELD
Field: Name
Data: Patrik
-Faltstrom
-Malin
-Linnerborg
#END FIELD
#BEGIN FIELD
Field: Email
Data: paf@bunyip.com
-malin.linnerborg@paf.se
# END FIELD
# END TEMPLATE
# END CENTROID-CHANGES
6.4 QUERY and POLLEES responses
The response to a QUERY command is done in WHOIS++ format.
6.5. Query referral
When referrals are included in the body of a response to a query,
each referral is listed in a separate SERVER-TO-ASK block as shown
below.
# SERVER-TO-ASK
Version-number: // version number of index software, used to insure
// compatibility
Body-of-Query: // the original query goes here
Server-Handle: // WHOIS++ handle of the referred server
Host-Name: // DNS name or IP address of the referred server
Port-Number: // Port number to which to connect, if different from the
// WHOIS++ port number
# END
Required/Optional table
Version-number REQUIRED, value should be 1.0
Body-of-query OPTIONAL
Server-Handle REQUIRED
Host-Name REQUIRED
Port-Number OPTIONAL, must be used if different from port 63
Example:
# SERVER-TO-ASK
Version-Number: 1.0
Server-Handle: SUNETSE01
Host-Name: sunic.sunet.se
Port-Number: 63
# END
7: Reply Codes
In addition to the reply codes listed in [Deutsch 95] for the basic
WHOIS++ client/server interaction, the following reply codes are used
in version 1.0 of this protocol.
113 Requested method not available Unable to provide a requested
compression method. Contacted
server will send requested
data in different format.
227 Update request acknowledged A DATA-CHANGED transmission
has been accepted and logged
for further action.
503 Required attribute missing A REQUIRED attribute is
missing in an interaction.
504 Desired server unreachable The desired server is
unreachable.
505 Desired server unavailable The desired server fails to
respond to requests, but host
is still reachable.
8. References
[Deutsch 95] Deutsch, et al., "Architecture of the WHOIS++ service",
RFC 1835, August 1995.
[Faltstrom 95] Faltstrom, P., et al., "How to Interact with a WHOIS++
Mesh, RFC 1914, February 1996.
9. Security Considerations
Security issues are not discussed in this memo.
10. Authors' Addresses
Chris Weider
Bunyip Information Systems, Inc.
310 St. Catherine St. West
Montreal, PQ H2X 2A1
CANADA
Phone: +1-514-875-8611
Fax: +1-514-875-6134
EMail: clw@bunyip.com
Jim Fullton
MCNC Center for Communications
Post Office Box 12889
3021 Cornwallis Road
Research Triangle Park
North Carolina 27709-2889
Phone: 410-795-5422
Fax: 410-795-5422
EMail: fullton@cnidr.org
Simon Spero
EMail: ses@eit.com