rfc2552.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

Network Working Group                                          M. Blinov
Request for Comments: 2552                                   M. Bessonov
Category: Informational                                     C. Clissmann
                                                           Teltec UCD-CS
                                                                 Ireland
                                                              April 1999

                Architecture for Information Brokerage
                        in the ACTS Project GAIA

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 (1999).  All Rights Reserved.

Abstract

   This memo introduces a domain and supplier independent generic
   architecture for information brokerage, designed as part of the ACTS
   project GAIA (Generic Architecture for Information Availability).

1. Introduction

   Today a huge number of goods and services are offered on the
   electronic market by a large, and ever-increasing, number of
   suppliers.  However, there is still no efficient way for a customer
   to find a product or information, he/she is interested in and a
   supplier that can provide that product.  Customers and suppliers
   already can not deal with the quantity of available information by
   themselves.  The high heterogeneity of existing protocols, formats,
   and underlying networks also limits development of the electronic
   market.

   This results in a demand for brokerage systems that can work as
   intermediary entities between customers and content suppliers.
   Brokerage systems assist a customer during the trading process and
   hide the heterogeneity and distribution of information from the
   customer.  The design of domain and supplier independent generic
   architecture for such brokerage systems is an objective of the
   project GAIA (Generic Architecture for Information Availability).
   GAIA received part funding from the EU ACTS programme for Research
   and Technological Development.  The GAIA brokerage system allows a
   customer to



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RFC 2552                          GAIA                        April 1999


   - search for a particular "product" (information, content or
     services) that he/she is interested in
   - locate the product, i.e. find supplier(s) from whom the product is
     available
   - order the product from the supplier
   - receive delivery of the product by digital means

   All these actions are carried out by the broker in response to
   requests from the customer.  Broker services are accessible to the
   customer through the unified user interface.  The customer system
   does not have to support all the protocols involved in the trading
   process.

   Full specification of the GAIA Architecture is available in the GAIA
   Standard [1].  The GAIA Standard includes a description of the GAIA
   Reference Model, GAIA Functional Architecture, GAIA Standard
   Profiles, and specification of the GAIA interfaces.

   This memo does not aim to include the whole text of the GAIA
   Standard, but to present the basic ideas and concepts of this
   standard.

   The structure of this memo follows the structure of the GAIA
   Standard:

   1.  The GAIA Reference Model provides a common basis for the
       description and specification of brokerage systems, including the
       GAIA system.

   2.  The GAIA Functional Architecture defines functional elements of
       the GAIA Broker, their roles and relationships.

   3.  The GAIA Brokerage System Interfaces describes internal and
       external interfaces of the GAIA brokerage system.

   4.  The GAIA Standard Profiles specifies mandatory and optional
       profiles to which brokerage systems may conform.

2.  The GAIA Reference Model

   The Generic Architecture for Information Availability (GAIA)
   Reference Model outlines the operations and actors involved in
   finding, ordering, and delivering physical and digital objects and
   services ("Products") in a global brokered distributed information
   environment.  It provides an overall view of the GAIA environment,
   and illustrates the respective roles of and relationships between its





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RFC 2552                          GAIA                        April 1999


   components.  Further work on standards and frameworks for individual
   components of the GAIA environment uses the model and terminology
   provided by the Reference Model.

   The GAIA environment is a collection of actors and functions that are
   combined to support a procedure for information and services
   discovery, order, and delivery.  The actors play roles in the
   procedure, including initiation and execution of the Actions which
   are combined to make up the overall transaction.  The GAIA
   architecture provides a standardised and widely applicable framework
   for the provision and implementation of the brokered search and
   retrieve applications in a large-scale networked environment.

2.1.  GAIA Roles

   The GAIA model considers three principal roles that can be played by
   the GAIA actors.  These are the Customer, the Broker and the
   Supplier.  These Roles are shown in Figure 1 below.  It also
   considers a further class of active entities who play supporting
   roles in the Actions.  This latter class is known as GAIA "Helpers"
   and includes, for example, authentication and payment.  The actors
   are organisations and individuals in the supply chain.  Every GAIA
   actor plays at least one role at any given time.

2.1.1.  The Customer

   The aim of the Customer is to obtain some Products or information
   about some Products.  The Customer role initiates the GAIA
   transaction by requesting one or more GAIA Actions, and receives the
   results of the transaction.  The Customer may deal with actors
   playing either of the other two roles: the Broker or the Supplier.
   These actors may themselves play the role of the Customer while
   requesting further services from other Brokers.

2.1.2.  The Broker

   The Broker provides brokerage services to the Customer and the
   Supplier.  It responds to requests from the Customer to provide
   Products, or information about Products.  The Products that the
   Broker supplies to the Customer may originate from one or more
   Suppliers and/or Brokers.  The Broker's primary role is to act as a
   collector and collator of information from a number of different
   Suppliers, and to supply this information to the Customer, thus
   obviating the need for the Customer to deal with a variety of
   Suppliers.  A Broker can also be considered to act on behalf of a
   Supplier, distributing information about the Products available.  The
   actor playing the role of the Broker may play the role of a Supplier




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   to a Customer or other Broker at the same time.  The Broker may play
   the role of a Customer while interacting with another Broker or with
   a Supplier.

2.1.3.  The Supplier

   The Supplier is the source of the Product supplied to the Customer.
   The Supplier provides the Broker with information about the Product
   that it can supply.  The Supplier may supply its Product directly to
   the Customer, or to the Broker for forwarding to the Customer.  An
   actor playing the role of a Supplier may also play the role of a
   Broker.  A Supplier may deal with a large number of Brokers and
   Customers over a number of GAIA transactions.

2.1.4.  Helpers

   A Helper is an application layer entity playing a supporting role in
   a GAIA transaction.  Helpers provide some service needed in the
   supply chain, but outside the core functionality of the Broker.
   Examples include a global directory service, payment service, or
   authentication service.

   The authentication Helper is concerned with facilitating the
   authentication of one actor to another.

   The payment Helper is concerned with supporting a mechanism for
   payment to one actor by another.

   In any given GAIA transaction, there will be one or more Customers
   (usually one), one or more Brokers, and one or more Suppliers.  A
   description of the Product sought by the Customer is provided by the
   Customer to the Broker.  The Broker may involve other Brokers in the
   search for the Product.  When a Supplier of the Product is discovered
   by the Broker, this information is included in the response of the
   Broker to the Customer.  During the course of the Action, it may be
   necessary to call upon the services of one or more Helpers.

2.2.  GAIA Actions

   Each GAIA transaction is made up of one or more Actions.  These
   Actions are requests by the Customer to the Broker or the Supplier to
   carry out some operation and to return a response.  Four Actions are
   defined:

   - Search
   - Locate
   - Order
   - Deliver



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RFC 2552                          GAIA                        April 1999


   These Actions are shown in Figure 1.

   +--------+    .   .    +--------+    .   .    +-----------+
   |        |-- Search -->|        |-- Search -->|           |+
   |        |    :   :    |        |    :   :    |           ||
   |        |-- Locate -->|        |-- Locate -->|           ||
   |Customer|    :   :    | Broker |    :   :    |Supplier(s)||
   |        |-- Order --->|        |-- Order --->|           ||
   |        |    :   :    |        |    :   :    |           ||
   |        |<- Deliver --|        |<- Deliver --|           ||
   +--------+    :   :    +--------+    :   :    +-----------+|
                 :   :                  :   :     +-----------+
                Helpers                Helpers
             <Authentication> <Payment> <Security>

   Figure 1 GAIA Roles and Actions

2.2.1.  Search

   The Search Action is carried out when the Customer asks the Broker to
   find some information on its behalf.  To do this, the Customer
   provides the Broker with some description of the Product it requires.
   On the basis of this description, the Broker carries out a search on
   behalf of the Customer and returns the result.  The result of a
   Search Action is a set of unique identifiers referencing the Products
   matching the description provided by the Customer.

2.2.2.  Locate

   The Locate Action is carried out when the Customer asks the Broker to
   provide it with information regarding the location and source of some
   Product.  To allow the Broker to do this, the Customer provides an
   unambiguous identification of the Product, which may be the result of
   a Search Action.  The Broker returns information to the Customer
   about a source or sources for the Product.  These data include the
   Terms of Availability information such as available methods of
   delivery, time of delivery, costs, etc.  However, this information
   can not be considered final since some special terms and conditions
   may apply, e.g. discounts for some categories of Customers.  The
   final version of the Terms of Availability is established during the
   negotiation phase of the Order Action.

2.2.3.  Order

   The Order Action is carried out when the Customer asks the Broker to
   obtain a Product on its behalf, or asks the Supplier to sell the
   Product directly to the Customer.  To enable an Order, the Customer
   provides the Broker/Supplier with Product source information, which



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RFC 2552                          GAIA                        April 1999


   may be a result of a Locate Action.  The Order Action consists of a
   negotiation phase and (possibly) a purchase phase.  During the
   negotiation phase the Customer obtains the quotation that contains
   the final version of the Terms of Availability for the (batch of)
   Products he is considering purchasing.  If the Customer finds these
   conditions satisfactory, he commits to the purchase.  Alternatively,
   if the Broker or Supplier supports telepresence services for the
   human interaction with the Supplier or Broker representatives, these
   may be used during the negotiations.

2.2.4.  Deliver

   The Deliver Action is carried out when the Broker provides the
   Customer with some requested Product.  The Product may be
   information, some physical object, or metadata.  The Deliver Action
   may be in response to an Order Action, a Search Action, or a Locate
   Action.

   While the Actions presented in this section may logically be taken to
   form an integrated sequence, this is not necessarily the case.
   Actions may take place independently, rather than as a part of a
   four-Action whole.  For example, Order and Deliver Actions may occur
   on the basis of information obtained by the Customer using some other
   mechanism than GAIA Search and Locate Actions.

2.3.  GAIA Helper Events

   During any of the GAIA Actions outlined above, it may be necessary to
   carry out some supporting activity.  These activities are called GAIA
   Helper events.  They include, for example, authentication and
   payment.  The Helper entities are involved in the GAIA events to
   provide services, additional to the GAIA Actions, to the GAIA actors.

   Authentication

   In order to verify the identity of one GAIA actor to another, an
   authentication exchange may need to take place.  This may occur
   during any of the GAIA Actions.  The manner or method of
   authentication is outside the scope of this document.

   Payment

   It may be necessary for payment to take place during a GAIA
   transaction.  In this situation, one GAIA actor pays one or more
   other GAIA actors.  The manner or method of payment is outside the
   scope of this document.