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Versions: 00 01 rfc2552                                                 
Network Working Group                                          M. Blinov
                                                             M. Bessonov
Category: Informational                                     C. Clissmann
                                                           Teltec UCD-CS
                                                            October 1998

           Generic Architecture for Information Availability

Status of This Memo

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Distribution of this document is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (1998).  All Rights Reserved.


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

1.  Introduction

   Nowadays a large number of goods and services are offered on the
   electronic market by a huge and growing 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
   it. Customers and suppliers already can not deal with so much
   available information by themselves. High heterogeneity of existing
   protocols, formats and underlying networks also limits development of
   the electronic market.

   This results in a demand for brokerage systems, which can work as
   intermediary entities between customers and content suppliers.
   Brokerage systems assist a customer during the trading process and
   hide 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's ACTS programme for Research and
   Technological Development.  The GAIA brokerage system allows a
   customer to

Blinov,Bessonov,Clissman      Informational                     [Page 1]

   - search for a particular "product" (information, content or services),
     which he/she is interested in
   - locate the product, i.e. find supplier(s),
     from which this 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 according to requests
   of 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], which is due to be published in November 1999. 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 basic ideas and concepts of this standard.

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

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

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

   3. The Technology Mapping, which explains how the functional
      requirements of the GAIA brokerage system are mapped to the
      existing technologies.

   4. The GAIA Standard Profiles, which 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
   components. Further work on standards and frameworks for individual
   components of the GAIA environment uses the model and terminology
   provided by the Reference Model.

Blinov,Bessonov,Clissman      Informational                     [Page 2]

   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, which can be played
   by the GAIA actors. These are the Customer, the Broker and the
   Supplier.  These Roles are shown in the 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 to a Customer or other
   Broker at the same time. It plays the role of a Customer while
   interacting with another Broker or with a Supplier.

Blinov,Bessonov,Clissman      Informational                     [Page 3]

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 or 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 respond to the Customer. Four
   Actions are defined

   - Search
   - Locate
   - Order
   - Deliver

   These Actions are shown in the Figure 1.

Blinov,Bessonov,Clissman      Informational                     [Page 4]

     +--------+    .   .    +--------+    .   .    +-----------+
     |        |-- Search -->|        |-- Search -->|           |+
     |        |    :   :    |        |    :   :    |           ||
     |        |-- Locate -->|        |-- Locate -->|           ||
     |Customer|    :   :    | Broker |    :   :    |Supplier(s)||
     |        |-- Order --->|        |-- Order --->|           ||
     |        |    :   :    |        |    :   :    |           ||
     |        |<- Deliver --|        |<- Deliver --|           ||
     +--------+    :   :    +--------+    :   :    +-----------+|
                   :   :                  :   :     +-----------+
                  Helpers                Helpers
               <Authenticat|on> <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. In order to do this, the
   Customer provides the Broker with some description of the Product
   which it requires. On the basis of this description, the Broker
   carries out a search on behalf of the Customer and returns the result
   to it. The result of a Search Action is a set of unique identifiers
   referencing the Products matching the description provided by the

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. In order 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 methods of
   delivery available, 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 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

Blinov,Bessonov,Clissman      Informational                     [Page 5]

   Product directly to the Customer. To enable Order, the Customer
   provides the Broker/Supplier with Product source information, which
   may be a result of a Locate Action. The Order Action consists of a
   negotiation phase and (possibly) a purchase phase. During the
   negotiations phase the Customer obtains the quotation which 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 section 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 authentication and payment. The Helper
   entities are involved in the GAIA events to provide services,
   additional to the GAIA Actions, to the GAIA actors.


   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.


   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.

Blinov,Bessonov,Clissman      Informational                     [Page 6]


   As part of any GAIA Action, it may be necessary to carry out some
   security operations, such as encryption of data, verification of
   source and content integrity of Product, or digital signature of some
   data entity or entities. The particular security services and
   mechanisms which may be required, or the manner, in which they may be
   provided, is outside the scope of this document.

3.  The GAIA Functional Architecture

3.1.  The Concept

   The GAIA Functional Architecture decomposes the overall functionality
   of the GAIA Broker into a number of components, and describes the
   roles and relationships of the components, and the manner in which
   they interoperate.

   In order to work in a heterogeneous environment the GAIA Functional
   Architecture introduces three levels of abstract elements of the
   Broker: the Kernel, Functional Unit Managers (FUMs), and Functional
   Units (FUs) (see Figure 2).

        GAIA Broker:
                       [  Kernel  ]                Kernel
                         /       \                 level
                        /         \
         [Functional Unit]     [Functional Unit]   Technology-independent
         [    Manager    ]     [    Manager    ]   action-dependent
              /    \                 /    \        level
             /      \               /      \
     [Functional][Functional] [Functional][Functional]  Technology
     [Unit      ][Unit      ] [Unit      ][Unit      ]  dependent

     Figure 2 Levels of the architecture

   Functional Units are the technology dependent parts of the
   architecture.  They perform required transactions in terms of a
   particular protocol.  All FUs are covered by a technology-independent
   interface. FUs are grouped according to the trading action they
   participate in, e.g. search FUs or locate FUs. Each group of FUs is
   governed by the corresponding Functional Unit Manager.

Blinov,Bessonov,Clissman      Informational                     [Page 7]

   Functional Unit Managers contain technology independent functions for
   particular actions. In order to use a particular technology FUM uses
   the services of attached FUs. There may be several FUs associated
   with a FUM, allowing the FUM to operate in different technology
   contexts.  There is one FUM in the system for every area of
   functionality, e.g.  search, locate, order. The Kernel is responsible
   for managing the activity of different FUMs (corresponding to
   different actions) and synchronising events between them.

   The GAIA Functional Architecture establishes the relationships
   between the existing technologies (standards and protocols) that are
   combined in the GAIA Standard, in the context of a brokerage system.
   It is to be expected that new technologies will evolve which will be
   viable alternatives to those selected. The abstract and modular
   nature of the Functional Architecture allows the replacement of one
   technology with a new one without disruption to the rest of the
   brokerage system.

3.2.  Functional Units

   The brokerage system provides a number of services to its users.
   These services are supported by the functions of the brokerage
   system. These include, for example,

   - searching
   - ordering
   - payment

   Each of these functions can be provided by a number of different
   candidate technologies. However, the operations that are required to
   be carried out remain the same - regardless of the selected
   technologies, the functional requirements do not change. The required
   operations are described in terms of abstract primitives, which can
   be mapped to the protocol instructions of the technology selected to
   support the function. A mapping component, called a Functional Unit
   (FU), is defined for each candidate technology, and converts calls to
   abstract primitives into protocol instructions. The FU acts as an
   adaptor between its particular technology and the rest of the
   brokerage system.

   Functional Units are defined for each candidate technology that can
   be used to fulfil a particular functional need of the brokerage
   system. A Functional Unit accepts abstract primitive invocations, and
   maps them to calls to the particular technology to which it is
   dedicated. The results of these calls are translated into the
   corresponding abstract primitives and returned by the FU, as shown in
   the Figure 3.

Blinov,Bessonov,Clissman      Informational                     [Page 8]

               * The rest of the Broker *
                      |  -abstract primitives
                   | Functional |
                   |    Unit    |
                      |  -technology-specific commands
               * Technology functions *

     Figure 3 GAIA Functional Unit

3.3.  Functional Unit Managers

   As noted above, a number of different candidate technologies can be
   used to fulfil a particular functional requirement of the brokerage
   system.  Depending on the details of the GAIA transaction (underlying
   network, Customer system capabilities, etc.), different technologies
   may be more useful during different transactions. As a result, each
   candidate technology has its own Functional Unit, which is invoked
   when that particular technology is required.

   A number of different Functional Units can exist which fulfil the
   same functional requirement of the brokerage system. In order to
   select the most appropriate FU (and technology), the brokerage system
   needs to know which is the most useful at any particular time,
   generally the one supported by the target Supplier system. This is
   the responsibility of the Functional Unit Manager, or FUM. Each
   function of the brokerage system has a single FUM, which is invoked
   in terms of abstract primitives by the Broker Kernel. This FUM
   selects the most appropriate of the candidate technologies, and calls
   the corresponding FU.

   The interface between the FUM and the corresponding FUs is defined
   for every FUM in an open, platform-independent, programming-language-
   independent manner. These interfaces do not depend on any particular
   technology. It allows configuring the set of technologies, supported
   by the Broker, by attaching different subsets of FUs. If a new
   technology is to be supported by the Broker, a new FU implementing
   this technology can be created according to the specification of the
   interface and attached to the corresponding FUM.

Blinov,Bessonov,Clissman      Informational                     [Page 9]

               |       Functional Unit Manager        |
                      ^                       ^
                      | -abstract primitives- |
                      v                       v
                 +------------+        +------------+
                 | Functional |        | Functional |
                 |    Unit    |        |    Unit    |
                 +------------+        +------------+
                  ^                                ^
                  | -technology-specific commands- |
                  v                                v
                * Technology *          * Technology *
                * functions  *          * functions  *

     Figure 4 Functional Unit Manager

3.4.  The Kernel

   The Kernel of the brokerage system acts as a bus for the transmission
   of abstract primitives between FUMs. Each FUM imports a set of
   abstract primitives, representing those services which the FUM
   expects to receive from some other part of the system. The services
   that the FUM is prepared to provide to other elements of the
   brokerage system are presented in the form of exported abstract
   primitives. All these abstract primitives are imported from, and
   exported to, the Kernel.

   The Kernel is also responsible for synchronisation of different
   actions within a transaction and for maintaining a common context
   between actions.

Blinov,Bessonov,Clissman      Informational                    [Page 10]

                  |           Broker Kernel             |
                       ^            ^              ^
                       | -abstract- | -primitives- |
                       v            v              v
                   +-------+     +-------+     +-------+
                   |  FUM  |     |  FUM  |     |  FUM  |
                   +-------+     +-------+     +-------+

        Figure 5 Broker Kernel

3.5.  Description of FUMs

   The core activities of the brokerage system include:

   1. searching for and Products that fit a user description
   2. sourcing Products the identification of which is known
   3. allowing users to order Products
   4. delivering information in file format
   5. delivering information as a continuous media stream
   6. providing a user interface to the brokerage services
   7. alerting users as to the availability of information
   8. interacting with external directory services
   9. authentication of other actors
   10. payment operations

   Each of these activities is carried out by the corresponding FUM as
   described below and shown in the Figure 6.

   Search FUM

   The Search FUM accepts requests to carry out a search for Products
   that fit a particular user description. It returns lists of
   identifiers of Products that fit the description.

   Locate FUM

   The Locate FUM accepts Product identifiers, and discovers where they
   may be obtained. It returns lists of Suppliers and locations for the

   Order FUM

   The Order FUM manages negotiations between a Customer and a Supplier,
   in order that agreement may be reached on the terms of availability
   of a particular Product or group of Products. Following the

Blinov,Bessonov,Clissman      Informational                    [Page 11]

                          The GAIA Broker:
     (Customer))   (Alerting))  (  DS   ))  (Auth))  (Payment))
     (   FUs  ))   (   FUs  ))  (  FUs  ))  ( FUs))  (  FUs  ))
     (e.g.HTTP))   (e.g. SMS))  (eg LDAP))  (    ))  (e.g.SET))
         \/            \/           \/        \/        \/
     [Customer]     [Alerting]    [ DS  ]  [ Auth ]  [Payment]
     [  FUM   ]     [  FUM   ]    [ FUM ]  [  FUM ]  [  FUM  ]
         |              |            |         |         |

      |                  Broker Kernel                      |
         |            |            |          |           |

     [ Search ]   [ Locate ]   [ Order ]  [ Stream ]  [ Item   ]
     [  FUM   ]   [  FUM   ]   [  FUM  ]  [Delivery]  [Delivery]
     [        ]   [        ]   [       ]  [  FUM   ]  [  FUM   ]
        /\            /\           /\         /\         /\
     ( Search  ))  ( Locate  ))  (Order ))  ( SD   ))  ( ID   ))
     (   FUs   ))  (   FUs   ))  ( FUs  ))  ( FUs  ))  ( FUs  ))
     (eg Z39.50))  (eg Z39.50))  (eg ILL))  (eg RTP))  (eg FTP))

     Figure 6 GAIA Functional Architecture

   negotiation phase, the Order FUM accepts purchase commitments from
   the Customer and forwards them to the Supplier. It returns a
   notification of the status of the order Action.

   Item Delivery FUM

   The Item Delivery FUM manages the delivery of file-structured items
   to the Customer.

   Stream Delivery FUM

   The Stream Delivery FUM manages the delivery of real-time multimedia
   data streams to the Customer.

   Customer FUM

   The Customer FUM provides an interface to support the Customer's
   systems interaction with the brokerage system.

   Alerting FUM

Blinov,Bessonov,Clissman      Informational                    [Page 12]

   The Alerting FUM notifies Customers about changes that may interest

   Directory Services FUM

   The Directory Services FUM provides an interface between an external
   directory service and the brokerage system.

   Authentication FUM

   The Authentication FUM provides a mechanism that allows a user to
   prove his identity to the brokerage system.

   Payment FUM

   The Payment FUM provides a mechanism for payment from one actor to

4.  Technology mapping

   This Chapter describes which particular technologies can be used to
   carry out different functions of the GAIA system.

4.1.  Internal Interfaces

   The definition of communications between functional components within
   the GAIA Broker is based on the OMG CORBA model [2]. Interfaces
   between components are defined on the IDL language, specified by OMG.
   Interface calls are passed between components by Object Request
   Broker (ORB).

   The advantage of this approach is that the specifications of the
   interfaces are platform- and programming-language-independent. These
   interfaces can be implemented using different programming languages
   on different platforms. All necessary conversions during interface
   invocations are transparently performed by an ORB. The CORBA model
   also allows installing different functional components of the GAIA
   Broker on different computers connected by a network. Interface calls
   will be transferred over the network by an ORB transparently for the

   The specification of the interfaces between the Kernel and FUMs and
   between each FUM and corresponding FUs is presented in the GAIA
   Standard [1].

Blinov,Bessonov,Clissman      Informational                    [Page 13]

4.2.  External protocols

   The GAIA Broker can use existing protocols to communicate with other
   actors. For example, it can use HTTP for interactions with Customers,
   Z39.50 for search, etc. As described in the GAIA Functional
   Architecture, support of particular technologies is provided by FUs.
   A set of supported protocols can be extended by attaching
   corresponding new FUs to a Broker. The GAIA Broker can support
   several protocols for each action. FUMs will select the most
   appropriate protocol for a transaction. The more protocols are
   supported by the Broker, the better service it can provide to
   Customers and Suppliers.

   The GAIA Standard does not limit the set of protocols supported by
   the Broker. However, for the purpose of interoperability, it
   specifies several GAIA profiles. These profiles aim to define the
   common subset of protocols (and a common range of protocol
   parameters), which is encouraged to be supported by Brokers in order
   to make possible communications between GAIA Brokers and with GAIA-
   aware Suppliers and Customers.

   Existing protocols are not the only way to contact the GAIA Broker.
   The GAIA interfaces have been designed as a generalisation of
   existing interfaces and protocols, so they provide more functionality
   than any particular protocol. In order to give access to full
   functionality of the GAIA Broker, the GAIA Standard allows users
   (Customers and other Brokers) to use directly the CORBA-defined
   Customer interface of the GAIA Broker (interface between Customer FUM
   and FUs) as shown in Figure 7. In this case the Customer system gets
   access to the Customer interface of the Broker using the service of
   an underlying ORB, and can request operations by calling
   corresponding methods of the interface.  This method allows avoiding
   convergence between a particular protocol and the GAIA interface.
   Where Customer and Supplier systems are not CORBA-aware, they can
   communicate with a GAIA Broker using existing protocols. If, however,
   they can use the service of an ORB, they are encouraged to
   communicate with a Broker by connecting to its Customer interface.
   The former way makes possible interactions with all existing types of
   Customer and Suppliers, using existing and widespread protocols. The
   later way has been designed to archieve maximum functionality by
   using native GAIA methods for communications with Customers and

4.3.  Supply Chains

   The operations of a brokerage system can be broken into three

Blinov,Bessonov,Clissman      Informational                    [Page 14]

                             |Broker          |
                             |                |
     +-----------+           |  [ Kernel ]    |
     |  Broker   |           |   --------     |
     |    or     |           |  [Customer]    |
     | Customer  |           |  [  FUM   ]    |
     |           |           |  ========== <-GAIA Customer
     |        *  |           |  *       *     | \interface
     | { O R B *}* * * * * * *{* O  R  B * }  |
     +-----------+    iiop   |            *   |         +----------+
                             |     (Customer) |         | Customer |
                             |     (   FU   ) |         |          |
                             +------------I---+         +----I-----+
                                           \      HTTP      /
                                            - - -      - - -

     Figure 7 External protocols and GAIA Customer interface

   - interactions with the Customer
   - interactions with other Brokers
   - interactions with Suppliers

   The first and last of these occur at the two ends of a supply chain,
   while inter-broker operations take place at other points in the
   chain.  The supply chain may take a number of different forms:

   - a minimal chain, where the Customer and the Broker are the ends of
     the chain, and there are no intervening links. In this case, the
     Broker plays the role of Supplier to the Customer.

   - a three-piece chain, where the Broker deals with the Customer and
     the Supplier, but not with any other Broker.

   - a longer chain, with one or more inter-broker operations.

4.3.1.  Minimal Supply Chains

   As discussed in the GAIA Reference Model, a GAIA transaction is
   composed of a number of actions, such as search, order and delivery.
   Each transaction is initiated by the Customer, who makes a request to
   the Broker. In the event that the Broker is able to fulfil the
   request, the transaction involves no other actors.

   In this simple case, the GAIA transaction involves the Customer and
   the Broker, and the only protocol which needs to be standardised is

Blinov,Bessonov,Clissman      Informational                    [Page 15]

     Minimal Supply Chain:
         +--------+         +-------------+
         |Customer| <=====> | Broker      |
         +--------+         |(as Supplier)|
     3-piece Supply Chain:
         +--------+       +--------+       +--------+
         |Customer| <===> | Broker | <===> |Supplier|
         +--------+       +--------+       +--------+
     Longer Supply Chain:
         +--------+       +--------+   +--------+       +--------+
         |Customer| <===> | Broker |<=>| Broker | <===> |Supplier|
         +--------+       +--------+   +--------+       +--------+

     Figure 8 Supply Chains

   that between the Customer and the Broker. This is specified in the
   GAIA Standard Minimal profile, below.

4.3.2.  Longer Supply Chains

   In the event that the Broker is not able to fulfil a request, the
   action may be propagated on to other Brokers, with the original
   Broker playing the Customer role. Each of these Brokers may in their
   turn propagate the request, if they cannot fulfil it.

   Eventually, if the action is successful, a Supplier will be found who
   can fulfil the request. The supply chain is thus made up a single
   Customer, one or more Suppliers, and one or more Brokers.

   In order to propagate an action from one Broker to another, a
   standardised communication protocol must be defined for broker-broker
   interaction. This is specified in the Basic profile, below. This
   profile is based on CORBA.

   Supplier and Brokers, however, are not obliged to support the Basic
   profile of the GAIA Standard. They may instead use another, more
   traditional, protocol, such as Z39.50 for discovery or ILL for
   ordering.  The Extension Modules to the GAIA Standard specify the
   profiles to be used for various brokerage functions.

5.  GAIA Standard Profiles

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5.1.  Introduction to Profiles and Modules

   The GAIA Standard defines a number of profiles, which a Broker may
   support in order to archive interoperability with other GAIA actors
   (Customer, Supplier and other Brokers). The complexity of the profile
   chosen by a Broker depends on the level and type of service which the
   Broker wishes to deliver in a GAIA-conformant manner. The higher the
   level of service which a Broker provides to a Customer, and the
   greater the length of the supply chain which the Broker wishes to
   support, the more advanced the profile, and/or the greater the number
   of extension modules the Broker must support.

   The profiles specified are

   - The Minimal profile, which is the very least
     to which a GAIA Broker must conform
   - The Basic Profile, which allows inter-broker communication
   - A number of Extension Modules, which allow the Broker
     to provide various services, and to interoperate with Suppliers,
     Brokers and Customers using protocols specified in the modules
   - A set of Interface Modules, that defines which particular
     Functional Unit CORBA interfaces are supported by the Broker

   Each Broker must conform at least to the Minimal profile to provide a
   web-based user interface. In addition, in order to take part in
   inter-broker communications, the Basic profile is recommended. For
   interaction with non-CORBA-aware entities, and for the use of
   advanced services, there are other modules of the standard to which
   the Broker may conform. These are denoted "Extension Modules", and
   they characterise the protocols and standards in a particular area of
   functionality. A Broker can choose an appropriate set of Extension
   Modules to conform to according to functionality it wishes to

   The GAIA Standard specifies all interfaces between FUM and FUs for
   the GAIA Broker. However, it would be too much to require every
   Broker to implement all of them. The GAIA Standard decomposes all
   interfaces into a number of Interface Modules. A Broker can choose a
   subset of Interface Modules, which is more important in its area of
   operation, and implement interfaces defined in these modules. These
   interfaces are important only inside the broker system and do not
   play any role in communication with other GAIA actors. However, a
   declaration of supported interfaces is important for the
   administrator to find in which areas the functionality of the Broker
   can be extended by attaching GAIA-conformant FUs.

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5.2.  Minimal Profile

   The minimum functionality that a Broker must support will allow it to
   provide services to the Customer as a part of a minimal chain. In
   this case, what is required of the Broker is simply a user interface
   for the Customer. Any further operations take place within the
   Broker, and so do not come within the scope of the standard.

   The Minimal profile requires the Broker to implement a user interface
   based on the HTTP 1.1 protocol, defined in RFC 2068 [3], and HTML
   2.0, defined in RFC 1866 [5]. It means that a Customer should be able
   to access the basic functionality of the GAIA Broker by using an HTTP
   1.1 and HTML 2.0 -conformant web-browser.

   It should be possible for Customers to locate a GAIA Broker. Thus a
   GAIA Broker should be registered in a Directory Service using a
   schema specified in the GAIA Standard [1].

   | Minimal Profile                                 |
   | Customer               | HTTP 1.1 (server),     |
   |                        | HTML 2.0               |

5.3.  Basic Profile

   While the minimal functionality is sufficient to allow a Broker to
   function, an important aspect of any GAIA Broker functionality is
   dealing with other Brokers. The goal of the Basic profile is to
   achieve federation between Brokers. Every GAIA Broker can use the
   service of other GAIA Broker in order to fulfil a request of a
   Customer. That Broker in turn can use the service of the third GAIA
   Broker. So every request can be chained by several Brokers. This
   extends the abilities of every GAIA action (Search, Locate, Order,
   etc.). Chained transactions are particularly important in the
   discovery phase of a transaction, where a Broker unable to fulfil a
   particular information requirement, passes on the search to another

   The Basic profile requires the Broker to implement the GAIA Customer
   interface defined in terms of CORBA. This is described in more detail
   in Section 4.2 above. It also requires the Broker to implement
   interface requestor procedures, i.e. to be able to connect to the
   Customer interfaces of other Brokers. The ORB used by the Broker
   should be conformant to the CORBA 2.0 specification [2] and use IIOP
   protocol for inter-ORB communications [2].

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   A full specification of the GAIA Customer interface is presented in
   the GAIA Standard [1].

   A GAIA Broker should be able to find other Brokers and Suppliers. It
   should also allow other participants to find it. Thus a GAIA Broker
   should support a directory service. The Basic profile includes a
   directory access protocol for this purpose. The actual choice of
   protocol is not standardised, because the choice does not influence
   the success of the Broker's inter-operation with other Brokers. The
   directory schema, which should be used, is specified in the GAIA

   The Basic profile suggested for a Broker to allow it to interoperate
   with other GAIA Brokers is as follows.

   | Basic Profile                                                  |
   | Customer               | GAIA Customer interface/IIOP (server) |
   | Search and Locate      | GAIA Customer interface/IIOP (client) |
   |        (Discovery)     |                                       |
   | Order                  | GAIA Customer interface/IIOP (client) |
   | Directory              | Some directory access protocol,       |
   |                        | such as LDAP                          |

5.4.  Extension Modules

   In order to allow Brokers to interoperate with other Brokers that do
   not support the Basic profile, and to allow Brokers to deal with
   Suppliers and Customers who are not CORBA-aware, as well as to allow
   delivery of items and data streams via the Broker, other open
   standards are suggested as extensions to the Basic and Minimal
   profiles. These standards reflect the results of the technology
   evaluation carried out as part of the project GAIA.

   The extra protocols are grouped into Extension Modules. Support of
   these Extension Modules is optional. A Broker can choose an
   appropriate set of Extension Modules to conform to according to the
   functionality it wishes to achieve. There is one Extension Module for
   each of the functional areas which are not covered by the Basic and
   Minimal Profiles, and also one Extension Module for each of the
   existing areas (Customer, Discovery and Order) to allow the use of
   protocols other than GAIA abstract primitives:

   - Discovery Extension Module
   - Order Extension Module

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   - Item Delivery Extension Module
   - Stream Delivery Extension Module
   - Security Extension Module
   - Payment Extension Module
   - Alerting Extension Module
   - Customer Discovery Extension Module

5.4.1.  Discovery Extension Module

   The Discovery Extension Module specifies the technologies to be used
   in searching for and locating on-line products and services.

   This Extension Module requires the Broker to support the client part
   of the Z39.50 protocol, as defined in [5]. The following subset of
   the protocol is required

   - Init, Search, and Present services
   - GRS-1 record syntax

   Z39.50 protocol PDUs should be carried using TCP/IP network protocol.

   | Discovery Extension Module                      |
   | Searching,             | Z39.50 (client)        |
   | Locating               |                        |

5.4.2.  Order Extension Module

   The Order Extension Module specifies the protocols to be used to
   order on-line products and services from a Supplier.

   This Extension Module requires the Broker to support all mandatory
   services of the client part of the ISO ILL protocol [6]. Basic
   conformance criteria should be adhered to. ILL protocol PDUs should
   be carried using TCP/IP network protocol.

   | Order Extension Module                          |
   | Order                  | ISO ILL (client)       |

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5.4.3.  Item Delivery Extension Module

   The Item Delivery Extension Module specifies the protocols and
   standards to be used for the delivery of on-line products and
   services to the Customer. There are two delivery scenarios considered

   - Direct Supplier to Customer delivery
     The delivery may be a single-step operation, with the Supplier
     supplying his product direct to the Customer, without the
     involvement of any Broker in the delivery process. The Broker may
     have acted to refer the Customer to the Supplier. In this case,
     where the Broker is not involved in delivery, the Item Delivery
     Extension Module does not apply.

   - Delivery over a supply chain with one or more Brokers involved
     In the event of the Broker being the central link in a supply chain
     of the form of Supplier-Broker-Customer, the Broker will use the
     protocols specified in the Item Delivery Extension Module to
     receive the product from the Supplier, and to provide the product
     to the Customer.

   The Item Delivery Extension Module requires the Broker to provide
   both FTP client and FTP server functionality [7], to allow the Broker
   to receive and to transmit files using FTP.

   The Item Delivery Extension Module requires the GAIA Broker also to
   be able to accept and to generate e-mail messages. The e-mail
   protocol specified is Internet e- mail, based on SMTP protocol [8]
   and mail data formats specified in RFC 822 [9]. This protocol is
   sufficient for the creation, transmission and management of textual
   e- mail messages.  However, for the transmission of data files of
   various types, extensions to the SMTP/RFC822 protocols are required.
   The mail extensions specified by the Item Delivery Extension Module
   are based on MIME (Multipurpose Internet Mail Extensions), defined in
   RFCs 2045-2049 [10]. Thus a GAIA Broker must be able to send and
   receive "simple" SMTP/RFC822 mail, and also be able to deal with RFC
   2045-2049 MIME mail extensions.

   For electronic document delivery the Item Delivery Extension Module
   requires the support of GEDI version 3.0.

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   | Item Delivery Extension Module                         |
   | FTP profile            | FTP [RFC 959] (client+server) |
   | Email profile          | Internet e-mail [SMTP,RFC822] |
   |                        |   (receiver+sender),          |
   |                        | MIME [RFC 2045-2049]          |
   | Document delivery      | GEDI version 3.0              |

5.4.4.  Stream Delivery Extension Module

   This Extension Module is intended to support real-time delivery of
   multimedia by the GAIA Broker.

   Several scenarios of stream delivery are considered. A stream can be

   - directly from a Supplier to a Customer
     The Broker does not take part in the stream delivery process, so
     this scenario is out of scope of this standard.

   - from a Supplier to a Customer via a Broker
     The Broker can add value to the stream delivery process by
     implementing cache algorithms, mixing streams, branching one stream
     to several Customers, etc.

   - from a Broker to a Customer
     The Broker can keep a small amount of multimedia data (e.g., audio
     examples) in its own database and deliver it to a Customer upon

   The Stream Delivery Extension Module is recommended to be implemented
   by a Broker in order to provide the last two scenarios of real-time
   multimedia delivery.

   The Stream Delivery Extension Module requires the Broker to support
   the following technologies

   - Compression
     MPEG-2 Audio Layer 3. Specified in ISO/IEC 13818-3 [11]. Only
     support of constrained parameter streams (CSPS) is required.

   - Data transfer protocol
     RTP protocol over UDP/IP, defined in RFC 1889 [12] (both client and
     server parts). It is recommended to support full behaviour of RTP
     application service entity ("translator" or "mixer") but it is not

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   - Mapping
     RTP payload format for MPEG Audio (MPA), defined in RFC 1890 [13].

   - Session control protocol
     RTCP, specified in RFC 1889 [12].

   This profile provides delivery of high quality audio over the
   networks with non- guaranteed quality of service such as the

   | Stream Delivery Extension Module                   |
   | Compression              | MPEG-2 Audio Layer 3    |
   | Data transfer            | RTP (client+server)     |
   | Mapping                  | RTP Audio Video Profile |
   | Session control protocol | RTCP                    |

5.4.5.  Security Extension Module

   The basic security services required for GAIA are

   - Authentication
     of users, remote servers (both as entity authentication and as
     bilateral peer-to-peer authentication), authentication of senders
     and receivers in network transactions, as well as the
     authentication of documents.  Authentication is required for three
     situations: authentication at the user workstation when starting
     the session, authentication in a local environment (client/server
     authentication) and authentication in a global, open network

   - Confidentiality
     and integrity of all resources transferred over the network or
     handled locally at application servers and user workstations.

   - Control of access to services and resources.

   - Non-repudiation of transactions, participants and sensitive

   This module allows a Broker to secure communications with other
   participants. It provides channel security, authentication, and
   certificate exchange.

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   The Security Extension Module specifies the following protocols and

   - Privacy, integrity, non-repudiation
     SSL v3.0 protocol, defined in [14].
     PKCS #7, defined in [15].

   - Remote, client/server authentication
     GSS v5, specified in RFC 1508 [16].

   - Certification services
     PKIX certification protocol, specified in [17].

   | Security Extension Module                                 |
   | Privacy, integrity, non-repudiation  | SSL v 3.0, PKCS #7 |
   | Remote, client/server authentication | GSS v5             |
   | Certification services               | PKIX certification |
   |                                      |      protocol      |

5.4.6.  Payment Extension Module

   This module allows a Broker to perform electronic payment operations
   with Customers, Suppliers and other Brokers. Such operations may take
   place at any stage during a GAIA transaction, during a search,
   locate, order or delivery action.

   The GAIA standard does not specify the tariffing or charging model to
   be used by a Broker, this is considered to be an internal matter.
   However, when a bill has been agreed, payment must take place in a
   secure and mutually acceptable manner. The payment procedure
   specified in the GAIA Standard makes use of the SET specification

   The Payment Extension Module requires for a Broker to support SET
   v1.0 merchant's server and SET certification protocol, specified in

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   | Payment Extension Module                           |
   | Payment                | SET v 1.0 :               |
   |                        | 1) CA server for banks    |
   |                        | 2) Cardholder wallet      |
   |                        | 3) Merchant Server        |
   |                        | 4) Payment Gateway server |

5.4.7.  Alerting Extension Module

   The Alerting Extension Module specifies the protocols to notify
   Customers about changes that can be interesting for them.

   This Extension Module requires the support of the following

   - Internet e-mail, based on SMTP protocol [8]
     and mail data formats specified in RFC 822 [9].
     The Broker should be able to generate and send e-mail messages.
   - SMS (Short Message Service), specified in [19].

   | Alerting Extension Module                           |
   | Alerting  | Internet e-mail [SMTP,RFC822] (sender), |
   |           | SMS                                     |

5.4.8.  Customer Discovery Extension Module

   The Customer Discovery Extension Module allows Z39.50 clients to use
   the service of the GAIA Broker.

   This Extension Module requires the Broker to support the server part
   of the Z39.50 protocol, as defined in [5]. The following subset of
   the protocol is required

   - Init, Search, and Present services
   - GRS-1 record syntax

   Z39.50 protocol PDUs should be carried using TCP/IP network protocol.

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   | Discovery Extension Module                         |
   | Searching,             | Z39.50 (server)           |
   | Locating               |                           |

5.5.  Interface Modules

   For the purpose of conformance all interfaces between FUM and FUs,
   specified by the GAIA Standard, are grouped into GAIA Interface
   Modules.  These modules are recommended to be supported by a GAIA
   Broker, but they are not mandatory. A Broker can choose a subset of
   Interface Modules, which is more important in its area of operation,
   and implement interfaces defined in these modules.

   The following table defines Interface Modules and specifies, which
   interfaces have to be supported in each of them.

   | Interface Module   | Interfaces that are required to be |
   |                    | supported in this module           |
   | Search             | Search FU interface                |
   | Locate             | Locate FU interface                |
   | Order              | Order FU interface                 |
   | Item Delivery      | Item Delivery FU interface         |
   | Stream Delivery    | Stream Delivery FU interface       |
   | Alerting           | Alerting FU interface              |
   | Directory Services | Directory Services FU interface    |
   | Authentication     | Authentication FU interface        |
   | Payment            | Payment FU interface               |

6.  Security Considerations

   Security issues related to the electronic brokerage are discussed in
   Sections 2.1.4, 2.3 and 5.4.5.

7.  References

   [1]  GAIA Consortium, Deliverable 0403, "GAIA Standard", November

   [2]  Object Management Group, "CORBA 2.0 Specification", July 1996,
        See <ftp://ftp.omg.org/pub/docs/formal/97-02-25.pdf>.

Blinov,Bessonov,Clissman      Informational                    [Page 26]

   [3]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Berners-Lee,
        T., "Hypertext Transfer Protocol -- HTTP/1.1", RFC 2068, January

   [4]  Berners-Lee, T., Connolly, D., "Hypertext Markup Language -
        2.0", RFC 1866, November 1995.

   [5]  ANSI/NISO Z39.50-1995 or ISO 23950 "Information Retrieval:
        Application Service Definition and Protocol Specification".

   [6]  ISO 10161:1997 "Information and documentation -- Open Systems
        Interconnection -- Interlibrary Loan Application Protocol

   [7]  Postel, J., Reynolds, J.K., "File Transfer Protocol", RFC 959,
        October 1985.

   [8]  Postel, J., "Simple Mail Transfer Protocol", RFC 821, August

   [9]  Crocker, D., "Standard for the format of ARPA Internet text
        messages", RFC 822, August 1982.

   [10] Freed, N., and N. Borenstein, "Multipurpose Internet Mail
        Extensions (MIME) Part One: Format of Internet Message Bodies",
        RFC 2045, November 1996.

        Freed, N., and N. Borenstein, "Multipurpose Internet Mail
        Extensions (MIME) Part Two: Media Types", RFC 2046, November

        Moore, K., "MIME (Multipurpose Internet Mail Extensions) Part
        Three: Message Header Extensions for Non-ASCII Text", RFC 2047,
        November 1996.

        Freed, N., Klensin, J., and J. Postel, "Multipurpose Internet
        Mail Extensions (MIME) Part Four: Registration Procedures", RFC
        2048, November 1996.

        Freed, N., and N. Borenstein, "Multipurpose Internet Mail
        Extensions (MIME) Part Five: Conformance Criteria and Examples",
        RFC 2049, November 1996.

   [11] ISO/IEC IS 13818 "Information technology -- Coding of moving
        pictures and associated audio information"

        Part 1: Systems
        Part 2: Video

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        Part 3: Audio
        Part 4: Conformance testing
        Part 5: Software simulation

   [12] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson,
        "RTP: A Transport Protocol for Real-Time Applications", RFC
        1889, Audio-Video Transport Working Group, January 1996.

   [13] Schulzrinne, H., "RTP Profile for Audio and Video Conferences
        with Minimal Control", RFC 1890, Audio-Video Transport Working
        Group, January 1996.

   [14] Freier, A., Karlton, P., Kocher, P., "The SSL Protocol - Version
        3.0", INTERNET-DRAFT, Transport Layer Security Working Group,
        November 1996,
        See <http://home.netscape.com/eng/ssl3/index.html>.

   [15] PKCS #7: Cryptographic Message Syntax Standard. Version 1.5,
        November 1993.

   [16] Linn, J., "Generic Security Service Application Program
        Interface", RFC 1508, Geer Zolot Associate, September 1993.

   [17] Public-Key Infrastructure (X.509) IETF Working Group,
        <http://www.ietf.org/html.charters/pkix-charter.html>, July 98.

   [18] "SET Secure Electronic Transaction Specification", Version 1.0,
        MasterCard and Visa, May 97.

   [19] Digital Cellular Telecommunications System (Phase 2+): Technical
        Realization of the Short Message Service (SMS) Point-to-Point
        (PP) (GSM 3.40). Version 5.2.0. European Telecommunications
        Standards Institute. May 1996.

8.  Authors' Addresses

   Mikhail Blinov
   Computer Science Department, University College Dublin,
   Belfield, Dublin 4, Ireland

   Phone: +353 1-706-2488
   Fax:   +353 1-269-7262
   EMail: mch@net-cs.ucd.ie

   Mikhail Bessonov
   Computer Science Department, University College Dublin,

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   Belfield, Dublin 4, Ireland

   Phone: +353 1-706-2488
   Fax:   +353 1-269-7262
   EMail: mikeb@net-cs.ucd.ie

   Ciaran Clissmann
   Computer Science Department, University College Dublin,
   Belfield, Dublin 4, Ireland

   Phone: +353 1-706-2488
   Fax:   +353 1-269-7262
   EMail: ciaranc@net-cs.ucd.ie

9.  Full Copyright Statement

   Copyright (C) The Internet Society (1998).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works. However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an

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