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RFC 2552 - Architecture for the Information Brokerage in the ACT


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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

   - 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

   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

   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

   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

   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.

   Security

   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 these components, and the manner in which
   they interoperate.

   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
                                                       level
    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.

   Functional Unit Managers contain technology independent functions for
   particular actions.  To use a particular technology an FUM uses the
   services of attached FUs.  There may be several FUs associated with
   an 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, and 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 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
   Figure 3.

             * The rest of the Broker *
                    ^
                    |  -abstract primitives
                    v
                 +------------+
                 | Functional |
                 |    Unit    |
                 +------------+
                    ^
                    |  -technology-specific commands
                    v
             * 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.  To select the
   most appropriate FU (and technology), the brokerage system needs to
   know which is the most useful at any particular time; in general this
   is the technology 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
   using abstract primitives by the Broker Kernel.  This FUM selects the
   most appropriate of the candidate technologies, and calls the
   corresponding FU (see Figure 4).

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

             +--------------------------------------+
             |       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
   (see Figure 5).

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

             +-------------------------------------+
             |           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 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 item 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 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
   Product.

   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
   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.

                        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 ]   [Discrete]
   [  FUM   ]    [  FUM   ]    [  FUM  ]   [Delivery]   [Delivery]
   [        ]    [        ]    [       ]   [  FUM   ]   [  FUM   ]
       /\            /\           /\           /\           /\
   ( Search  ))  ( Locate  ))  (  Order   ))  ( SD   ))  ( DD   ))
   (   FUs   ))  (   FUs   ))  (  FUs     ))  ( FUs  ))  ( FUs  ))
   (eg Z39.50))  (eg Z39.50))  (eg ISO ILL))  (eg RTP))  (eg FTP))

   Figure 6 GAIA Functional Architecture

   Discrete Delivery FUM

   The Discrete Delivery FUM manages the delivery of discrete 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

   The Alerting FUM notifies Customers about changes that may interest
   them.

   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
   another.

4.  GAIA Brokerage System Interfaces

   This Chapter describes the internal and external interfaces of the
   GAIA brokerage system.

4.1.  Internal Interfaces

   The definition of communication between functional components within
   the GAIA Broker is based on the OMG CORBA model [2].  Interfaces
   between components are defined in the IDL language specified by OMG.
   Interface calls are passed between components by the 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 application.

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

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 for particular technologies is
   provided by FUs.  A set of supported protocols can be extended by
   attaching the corresponding new FUs to a Broker.  The GAIA Broker can
   support several protocols for each action.  The FUMs will select the
   most appropriate protocol for a transaction.  The more protocols
   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 define a common
   subset of protocols (and a common range of protocol parameters) that
   Brokers are encouraged to support in order to make communication
   between GAIA Brokers, and with GAIA-aware Suppliers and Customers,
   possible.

   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.  To give access to the full
   functionality of the GAIA Broker, the GAIA Standard allows users
   (Customers and other Brokers) to directly use the CORBA-defined
   Customer interface of the GAIA Broker (interface between the 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 the
   corresponding methods of the interface.  The Customer interface of
   the GAIA Broker is specified in the GAIA Standard [1].

   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.
   This method allows for avoiding convergence between a particular
   protocol and the GAIA interface.  The former method makes
   interactions with all existing types of Customers and Suppliers
   possible using existing and widespread protocols.  The later method
   has been designed to achieve maximum functionality by using native
   GAIA methods for communication with Customers and Suppliers.

                              +----------------+
                              |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 the GAIA Customer interface

5.  GAIA Standard Profiles

   The GAIA Standard defines a number of profiles, which a Broker may
   support in order to achieve interoperability with other GAIA actors
   (Customers, Suppliers 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 that 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.

5.1.  Supply Chains

   The GAIA profile definition approach is based on the possible types
   of supply chain that a brokerage system can be a part of.

   The operations of a brokerage system can be broken into three
   categories:

   - 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 interbroker 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 interbroker operations.

      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

5.1.1.  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.  The only protocol which needs to be standardised is that
   between the Customer and the Broker.  This is specified in the GAIA
   Standard Minimal profile below.

5.1.2.  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 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 ISO ILL for
   ordering.  The Extension Modules to the GAIA Standard specify the
   profiles to be used for various brokerage functions.

5.2.  Introduction to the GAIA Standard Profiles and Modules

   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, 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 the functionality it wishes to
   achieve.

   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 that are 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 the areas in which the functionality of the
   Broker can be extended by attaching GAIA-conformant FUs.

5.3.  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 [4].  It means that a Customer should be
   able to access the basic functionality of the GAIA Broker by using a
   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               |
   +------------------------+------------------------+

5.4.  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 Brokers 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
   Broker.

   The Basic profile requires the Broker to implement the GAIA Customer
   interface defined in terms of CORBA.  This interface is described in
   more detail in Section 4.2 above.  The Basic profile 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].

   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
   Standard.

   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                          |
   +------------------------+---------------------------------------+

5.5.  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
   technologies are suggested as extensions to the Basic and Minimal
   profiles.  These technologies 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.

   The following Extension Modules are defined.

   - Discovery Extension Module
   - Order Extension Module
   - Discrete Delivery Extension Module
   - Stream Delivery Extension Module
   - Security Extension Module
   - Payment Extension Module
   - Alerting Extension Module
   - Customer Discovery Extension Module

5.5.1.  Discovery Extension Module

   The Discovery Extension Module specifies the technologies to be used
   in searching for and locating 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
   protocols.

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

5.5.2.  Order Extension Module

   The Order Extension Module specifies the protocols to be used to
   order 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.  ISO ILL protocol PDUs
   should be carried using TCP/IP network protocols.

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

5.5.3.  Discrete Delivery Extension Module

   The Discrete 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 directly 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 Discrete 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 Discrete Delivery Extension Module to
     receive the product from the Supplier, and to provide the product
     to the Customer.

   The Discrete 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 Discrete Delivery Extension Module also requires the GAIA Broker
   to be able to accept and to generate e-mail messages.  The e-mail
   protocol specified is Internet e-mail, based on the 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 Discrete 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 Discrete Delivery Extension
   Module requires the support of GEDI version 3.0.

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

5.5.4.  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
   delivered

   - directly from a Supplier to a Customer
     The Broker does not take part in the stream delivery process; 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
     request.

   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 that the full behaviour of an RTP
     application service entity ("translator" or "mixer") is supported
     but it is not required.

   - Mapping
     RTP payload format for MPEG Audio (MPA), defined in RFC 2250 [13].

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

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

   +----------------------------------------------------+
   | Stream Delivery Extension Module                   |
   +--------------------------+-------------------------+
   | Compression              | MPEG-2 Audio Layer 3    |
   | Data transfer            | RTP (client+server)     |
   | Mapping                  | RFC 2250                |
   | Session control protocol | RTCP                    |
   +--------------------------+-------------------------+

5.5.5.  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),
     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
     (Internet).

   - 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
     documents.

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

   The Security Extension Module specifies the following protocols and
   algorithms:

   - 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      |
   +--------------------------------------+--------------------+

5.5.6.  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 Deliver 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 a Broker to support SET v1.0
   merchant's server and SET certification protocol, specified in [18].

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

5.5.7.  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
   technologies:

   - 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                                     |
   +-----------+-----------------------------------------+

5.5.8.  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
   protocols.

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

5.6.  Interface Modules

   For the purpose of conformance, all interfaces between FUMs 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 that are more important in its area of operation,
   and implement interfaces defined in these modules.

   A full specification of the Functional Unit interfaces is presented
   in the GAIA Standard [1].

   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                 |
   | Discrete Delivery  | Discrete Delivery FU interface     |
   | Stream Delivery    | Stream Delivery FU interface       |
   | Customer           | Customer FU interface              |
   | Alerting           | Alerting FU interface              |
   | Directory Services | Directory Services FU interface    |
   | Authentication     | Authentication FU interface        |
   | Payment            | Payment FU interface               |
   +--------------------+------------------------------------+

6.  Acknowledgement

   We wish to express our gratitude to all members of the GAIA
   Consortium for a very lively discussion and their valuable direct and
   indirect input in the design process of the GAIA Standard.

7.  Security Considerations

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

8.  References

   [1]  GAIA Consortium, Deliverable 0403, "GAIA Standard (Final)",
        December 1998, see also <http://www.syspace.co.uk/GAIA/>.

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

   [3]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H. and T.
        Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC
        2068, January 1997.

   [4]  Berners-Lee, T. and D. Connolly, "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
        Specification".

   [7]  Postel, J. and J. Reynolds, "File Transfer Protocol", STD 9, RFC
        959, October 1985.

   [8]  Postel, J., "Simple Mail Transfer Protocol", STD 10, RFC 821,
        August 1982.

   [9]  Crocker, D., "Standard for the format of ARPA Internet text
        messages", STD 11, 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
        1996.

        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
        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, January 1996.

   [13] Hoffman, D., Fernando, G., Goyal, V. and M. Civanlar, "RTP
        Payload Format for MPEG1/MPEG2 Video", RFC 2250, January 1998.

   [14] Freier, A., Karlton, P. and P. Kocher, "The SSL Protocol -
        Version 3.0", Work in Progress, 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.

9.  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
   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

10.  Full Copyright Statement

   Copyright (C) The Internet Society (1999).  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
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   kind, provided that the above copyright notice and this paragraph are
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   the copyright notice or references to the Internet Society or other
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   The limited permissions granted above are perpetual and will not be
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   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
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