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
Blinov, et al. [Page 1]RFC 2552 GAIA April 1999
- search for a particular "product" (information, content or
services) that he/she is interested in
- locate the product, i.e. find supplier(s) from whom the product is
available
- order the product from the supplier
- receive delivery of the product by digital means
All these actions are carried out by the broker in response to
requests from the customer. Broker services are accessible to the
customer through the unified user interface. The customer system
does not have to support all the protocols involved in the trading
process.
Full specification of the GAIA Architecture is available in the GAIA
Standard [1]. The GAIA Standard includes a description of the GAIA
Reference Model, GAIA Functional Architecture, GAIA Standard
Profiles, and specification of the GAIA interfaces.
This memo does not aim to include the whole text of the GAIA
Standard, but to present the basic ideas and concepts of this
standard.
The structure of this memo follows the structure of the GAIA
Standard:
1. The GAIA Reference Model provides a common basis for the
description and specification of brokerage systems, including the
GAIA system.
2. The GAIA Functional Architecture defines functional elements of
the GAIA Broker, their roles and relationships.
3. The GAIA Brokerage System Interfaces describes internal and
external interfaces of the GAIA brokerage system.
4. The GAIA Standard Profiles specifies mandatory and optional
profiles to which brokerage systems may conform.
2. The GAIA Reference Model
The Generic Architecture for Information Availability (GAIA)
Reference Model outlines the operations and actors involved in
finding, ordering, and delivering physical and digital objects and
services ("Products") in a global brokered distributed information
environment. It provides an overall view of the GAIA environment,
and illustrates the respective roles of and relationships between its
Blinov, et al. [Page 2]RFC 2552 GAIA April 1999
components. Further work on standards and frameworks for individual
components of the GAIA environment uses the model and terminology
provided by the Reference Model.
The GAIA environment is a collection of actors and functions that are
combined to support a procedure for information and services
discovery, order, and delivery. The actors play roles in the
procedure, including initiation and execution of the Actions which
are combined to make up the overall transaction. The GAIA
architecture provides a standardised and widely applicable framework
for the provision and implementation of the brokered search and
retrieve applications in a large-scale networked environment.
2.1. GAIA Roles
The GAIA model considers three principal roles that can be played by
the GAIA actors. These are the Customer, the Broker and the
Supplier. These Roles are shown in Figure 1 below. It also
considers a further class of active entities who play supporting
roles in the Actions. This latter class is known as GAIA "Helpers"
and includes, for example, authentication and payment. The actors
are organisations and individuals in the supply chain. Every GAIA
actor plays at least one role at any given time.
2.1.1. The Customer
The aim of the Customer is to obtain some Products or information
about some Products. The Customer role initiates the GAIA
transaction by requesting one or more GAIA Actions, and receives the
results of the transaction. The Customer may deal with actors
playing either of the other two roles: the Broker or the Supplier.
These actors may themselves play the role of the Customer while
requesting further services from other Brokers.
2.1.2. The Broker
The Broker provides brokerage services to the Customer and the
Supplier. It responds to requests from the Customer to provide
Products, or information about Products. The Products that the
Broker supplies to the Customer may originate from one or more
Suppliers and/or Brokers. The Broker's primary role is to act as a
collector and collator of information from a number of different
Suppliers, and to supply this information to the Customer, thus
obviating the need for the Customer to deal with a variety of
Suppliers. A Broker can also be considered to act on behalf of a
Supplier, distributing information about the Products available. The
actor playing the role of the Broker may play the role of a Supplier
Blinov, et al. [Page 3]
RFC 2552 GAIA April 1999
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
Blinov, et al. [Page 4]
RFC 2552 GAIA April 1999
These Actions are shown in Figure 1.
+--------+ . . +--------+ . . +-----------+
| |-- Search -->| |-- Search -->| |+
| | : : | | : : | ||
| |-- Locate -->| |-- Locate -->| ||
|Customer| : : | Broker | : : |Supplier(s)||
| |-- Order --->| |-- Order --->| ||
| | : : | | : : | ||
| |<- Deliver --| |<- Deliver --| ||
+--------+ : : +--------+ : : +-----------+|
: : : : +-----------+
Helpers Helpers
<Authentication> <Payment> <Security>
Figure 1 GAIA Roles and Actions
2.2.1. Search
The Search Action is carried out when the Customer asks the Broker to
find some information on its behalf. To do this, the Customer
provides the Broker with some description of the Product it requires.
On the basis of this description, the Broker carries out a search on
behalf of the Customer and returns the result. The result of a
Search Action is a set of unique identifiers referencing the Products
matching the description provided by the Customer.
2.2.2. Locate
The Locate Action is carried out when the Customer asks the Broker to
provide it with information regarding the location and source of some
Product. To allow the Broker to do this, the Customer provides an
unambiguous identification of the Product, which may be the result of
a Search Action. The Broker returns information to the Customer
about a source or sources for the Product. These data include the
Terms of Availability information such as available methods of
delivery, time of delivery, costs, etc. However, this information
can not be considered final since some special terms and conditions
may apply, e.g. discounts for some categories of Customers. The
final version of the Terms of Availability is established during the
negotiation phase of the Order Action.
2.2.3. Order
The Order Action is carried out when the Customer asks the Broker to
obtain a Product on its behalf, or asks the Supplier to sell the
Product directly to the Customer. To enable an Order, the Customer
provides the Broker/Supplier with Product source information, which
Blinov, et al. [Page 5]RFC 2552 GAIA April 1999
may be a result of a Locate Action. The Order Action consists of a
negotiation phase and (possibly) a purchase phase. During the
negotiation phase the Customer obtains the quotation that contains
the final version of the Terms of Availability for the (batch of)
Products he is considering purchasing. If the Customer finds these
conditions satisfactory, he commits to the purchase. Alternatively,
if the Broker or Supplier supports telepresence services for the
human interaction with the Supplier or Broker representatives, these
may be used during the negotiations.
2.2.4. Deliver
The Deliver Action is carried out when the Broker provides the
Customer with some requested Product. The Product may be
information, some physical object, or metadata. The Deliver Action
may be in response to an Order Action, a Search Action, or a Locate
Action.
While the Actions presented in this section may logically be taken to
form an integrated sequence, this is not necessarily the case.
Actions may take place independently, rather than as a part of a
four-Action whole. For example, Order and Deliver Actions may occur
on the basis of information obtained by the Customer using some other
mechanism than GAIA Search and Locate Actions.
2.3. GAIA Helper Events
During any of the GAIA Actions outlined above, it may be necessary to
carry out some supporting activity. These activities are called GAIA
Helper events. They include, for example, authentication and
payment. The Helper entities are involved in the GAIA events to
provide services, additional to the GAIA Actions, to the GAIA actors.
Authentication
In order to verify the identity of one GAIA actor to another, an
authentication exchange may need to take place. This may occur
during any of the GAIA Actions. The manner or method of
authentication is outside the scope of this document.
Payment
It may be necessary for payment to take place during a GAIA
transaction. In this situation, one GAIA actor pays one or more
other GAIA actors. The manner or method of payment is outside the
scope of this document.
Blinov, et al. [Page 6]
RFC 2552 GAIA April 1999
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.
Blinov, et al. [Page 7]RFC 2552 GAIA April 1999
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.
Blinov, et al. [Page 8]
RFC 2552 GAIA April 1999
* 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.
Blinov, et al. [Page 9]RFC 2552 GAIA April 1999
+--------------------------------------+
| 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
Blinov, et al. [Page 10]RFC 2552 GAIA April 1999
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.
Blinov, et al. [Page 11]
RFC 2552 GAIA April 1999
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.
Blinov, et al. [Page 12]RFC 2552 GAIA April 1999
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
Blinov, et al. [Page 13]
RFC 2552 GAIA April 1999
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.
Blinov, et al. [Page 14]
RFC 2552 GAIA April 1999
+----------------+
|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:
Blinov, et al. [Page 15]RFC 2552 GAIA April 1999
- 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.
Blinov, et al. [Page 16]RFC 2552 GAIA April 1999
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.
Blinov, et al. [Page 17]RFC 2552 GAIA April 1999
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].
Blinov, et al. [Page 18]
RFC 2552 GAIA April 1999
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.
Blinov, et al. [Page 19]
RFC 2552 GAIA April 1999
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.
Blinov, et al. [Page 20]
RFC 2552 GAIA April 1999
+-------------------------------------------------+
| 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.
Blinov, et al. [Page 21]RFC 2552 GAIA April 1999
+--------------------------------------------------------+
| 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.
Blinov, et al. [Page 22]RFC 2552 GAIA April 1999
- 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
Blinov, et al. [Page 23]RFC 2552 GAIA April 1999
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 |
+------------------------+---------------------------+
Blinov, et al. [Page 24]RFC 2552 GAIA April 1999
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
Blinov, et al. [Page 25]RFC 2552 GAIA April 1999
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.
Blinov, et al. [Page 26]RFC 2552 GAIA April 1999
[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
Blinov, et al. [Page 27]RFC 2552 GAIA April 1999
[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.
Blinov, et al. [Page 28]RFC 2552 GAIA April 1999
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
Blinov, et al. [Page 29]
RFC 2552 GAIA April 1999
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
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
English.
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
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Blinov, et al. [Page 30]
