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3.3.1 Acceptable User Input
User Input is defined in terms of
- Searchable Attributes
- Matching semantics
- Character sets
These, in conjunction with the DAG schema, defined in Appendix A,
form the basis of the required query expression. Individual queries
are discussed in more detail in the Client Access Point (DAG-CAP)
component descriptions for supported protocols.
Supported Query Types
The DAG system is designed to support fragment-matching queries on a
limited set of data attributes -- "Name", "Organizational Role",
"Organization", and "Locality". The selected permissible query
combinations of attributes are listed in Table 3.1. From the table
it can be seen that not all combinations of the three attributes are
supported -- only those that are needed for the desired
functionality.
Symbol Description
------- -----------
N Name
NL Name + Locality
NO Name + Organization
NOL Name + Organization + Locality
RO Role + Organization
ROL Role + Organization + Locality
Table 3.1 DAG-supported queries
The RO and ROL queries are separated from the rest as they are
searches for "virtual" persons -- roles within an organization (e.g.,
president, or customer service desk) for which one might want to find
contact information.
Matching Semantics
As befits the individual client query protocols, more string matching
expressions may be provided. The basic semantics of the DAG expect
the following to be available in all client access software (as
relevant):
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RFC 2967 TISDAG October 2000
- Full word, exact match
- Word substring match (E.g., "cat" would match "scatter")
- Case-sensitive and case-insensitive matching
TISDAG: LDAP/X.500, supports case-sensitivity as such but some of
the most used attributes, such as the commonName attribute, are
defined in the standard to be of the case-insensitive
attributetypes. The impact on the DAG system is that even if the
index collected from a LDAP/X.500 server might have upper and
lower case letters in the tokens, they can not be handled as such
since that would be inferring meaning in something which is
natively regarded as meaningless. The conclusion of the above is
that The Referral Index should be case-insensitive and case-
sensitivity should be supported by the SAPs if the native access
protocol supports it.
Character Sets
Wherever possible, the DAG System supports and promotes the use of
Unicode Version 2.0 for character sets (see [21]) specifically the
UTF-8 encoding (see Appendix A.2 of [21] or [20]) Accommodation is
made, where necessary, to support the deployed base of existing
software.
Specifically:
DAG/IP: All internal communications using the DAG/IP are carried out
in UTF-8.
TISDAG: not just UTF-8, but UTF-8 based on composed UNICODE
version 2 character encodings.
DAG-CAP input: Where specific access protocols permit selection of
character sets, DAG-CAPs must support UTF-8. They may additionally
support other anticipated character set encodings.
DAG-SAP communications with WDSPs: Where specific access protocols
permit selection of character sets, DAG-SAPs must support UTF-8 and
use UTF-8 whenever the remote WDSP supports it. They may
additionally support other character set encodings.
CIP Index Objects: The Index Objects supplied by the WDSPs to the DAG
system shall contain data encoded in UTF-8.
TISDAG: The same limitation as for DAG/IP, that is the basic data
should be UTF-8 encoded composed UNICODE version 2 character
encodings.
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RFC 2967 TISDAG October 2000
3.3.2 Data Output Spec
Schema Definition
The schema used for the DAG service is defined in Appendix A. This
is a very basic information schema, intended to carry the necessary
information for the DAG service, and not more. Although generic
"whitepages" schema definitions do exist the more sophisticated and
detailed the information presentation, the more difficult it is to
map the schema seamlessly across protocols of different paradigms.
Thus, the "KISS" ("Keep it simple, sir") principle seems appropriate
here.
Individual DAG-CAPs define how they express this schema.
Referral Definition
For client access protocols that make use of the concept of
referrals, DAG-CAP definitions will define the expression of
referrals in those protocols. The DAG/IP defines the expression of
referrals (see Appendix C).
Error conditions
Each DAG-CAP may provide more detailed error messages, but will
define minimally the support for the following error conditions:
- unrecognized query
- too many hits
Apart from these errors, the DAG-CAP may choose to refuse a query by
redirecting the end-user to a different DAG-CAP of the same protocol.
3.4 Directory Server Interface
The DAG will use the Common Indexing Protocol (CIP) server-server
protocol to obtain updated index objects from WDSPs. For query-
routing purposes, WDSPs are expected to provide Whois++, LDAPv2 or
LDAPv3 interface to their data (although their preferred access may
be something completely different). N.B.: In the responses from the
technical survey, all respondents currently provide access to their
service in one of these protocols.
In order to provide a useful and uniform service, WDSPs are expected
to provide 7x24 access to their whitepages information. WDSPs are
also expected to implement operations, administration, maintenance,
and provisioning processes designed to minimize service down time for
both planned and unplanned administration and maintenance activities.
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RFC 2967 TISDAG October 2000
4.0 Architecture
4.1 Software Components
The conceptual architecture of the DAG is represented in Figure 4.1.
General architectural specifications are described below, followed by
individual component specifications Sections 5.5 through 5.12.
4.1.1 Internal Communications
Communications between components of the DAG will be by TCP/IP
connections, using the DAG-Internal Protocol (DAG/IP). DAG/IP is
used by DAG-CAPs to communicate with the Referral Index and DAG-SAPs.
Thus, the DAG/IP defines
- the DAG-CAPs' range of query ability in the Referral Index (to
gather referrals in response to the end-user's requests)
- the responses (and their formats) of the Referral Index to the
DAG-CAP requests
- the DAG-CAPs' range of query ability to the DAG-SAPs for pursuing
referrals when the DAG-CAP needs to do chaining for the client
access software
- the responses (and their formats) of the DAG-SAPs to the DAG-CAPs.
The detail of the planned DAG/IP is given in Appendix C. The detail
of the DAG-CAP--Referral Index and DAG-CAP--DAG-SAP interactions is
given in the definitions of individual DAG-CAPs and DAG-SAPs, below
(Sections 5.5 through 5.12).
4.1.2 Referral Index
The Referral Index is responsible for maintaining the index of WDSP
information, and providing a list of reasonable referrals in response
to DAG-CAP search requests. These "referrals" provide pointers to
identify WDSPs that may have information that matches the end-user's
query.
4.1.3 DAG-CAPs
Individual DAG-CAPs are responsible for providing a particular client
access protocol interface to the DAG service. DAG-CAPs receive end-
user queries in a particular query access protocol, convert the
request into a query for the Referral Index ( i.e., expressed in
DAG/IP), and then convert the Referral Index's response into a form
that is appropriate for the client access protocol. This may mean
passing back the referrals directly, calling on DAG-SAPs to do the
work of translating the referral into results ("chaining"), or a
combination of both.
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RFC 2967 TISDAG October 2000
+-------------------------------------+
|+====+ |
HTTP <-->+| |<------+ (Full chaining) |
|| | | |
|+====+ | |
| | +----+|
| | Referral-->| ||
| | Result <--| |+<--> Whois++
| | +----+|
|+====+ | |
SMTP <-->+| |<------+ (Full chaining) |
|| | | |
|+====+ | |
| | +----+|
| | Referral-->| ||
| | Result <--| |+<--> LDAPv2
| | +----+|
|+====+ | |
Whois++<-->+| |<------+ (Chain LDAPv2/3) |
|| | | |
|+====+ | |
| | +----+|
| | Referral-->| ||
| | Result <--| |+<--> LDAPv3
| | +----+|
|+====+ | |
LDAPv2 <-->+| |<------+ (Full chaining) |
|| | | |
|+====+ | |
| | |
|+====+ | |
LDAPv3 <-->+| |<------+ (Chain Whois++) |
|| | | |
|+====+ | |
| | |
| v |
| +-----------------------+ |
| | Referral Index |<---------------> Common
| | | | Indexing Protocol
| +-----------------------+ | (CIP)
+-------------------------------------+
All internal communications are in DAG/IP.
Figure 4.1 Conceptual Architecture of the DAG
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RFC 2967 TISDAG October 2000
4.1.4 DAG-SAPs
Individual DAG-SAPs are called upon (by DAG-CAPs) to take DAG-
generated referrals and pursue them -- issuing the indicated query at
the specified WDSP service. Results from individual WDSPs are
converted back into DAG/IP-specific format for the DAG-CAP that made
the request. Each DAG-SAP is responsible for handling referrals to
WDSPs of a particular protocol (e.g., LDAPv2, Whois++, etc).
4.2 Important Architectural Notes
This section notes some of the thinking that has driven the
architectural and software design specification for the DAG system.
This helps to provide the context in which to understand the software
specifications that follow, and should give clues for the eventual
extension of the DAG system. This section also acts, in some ways,
as an FAQ (Frequently Asked Questions) section, as the content is
shaped by questions received during the tech spec development phase.
It attempts to illuminate context that may not otherwise be apparent
on a first reading of the software specifications.
4.2.1 2 Distinct Functions: Referrals and Chaining
At all times, it must be kept in mind that the primary function of
the DAG system is to provide users with referrals to WDSP services
that may have the information they seek. Since it is the case that
not all supported client protocols can handle referrals, the DAG
system also provides a chaining service to pursue referrals that the
user's client software cannot handle itself. This chaining service
does attempt to match the user's query against data from WDSPs, but
this is to be seen as a secondary, or support function of the DAG
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