INTERNET DRAFT EXPIRES JULY 199 INTERNET DRAFT
Network Working Group M. Blinov
M. Bessonov
Category: Informational C. Clissmann
Teltec UCD-CS
Ireland
October 1998
Generic Architecture for Information Availability
<draft-rfced-info-blinov-01.txt>
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Abstract
This memo introduces a domain and supplier independent generic
architecture for the information brokerage, designed as a part of the
ACTS project GAIA (Generic Architecture for Information
Availability).
1. Introduction
Nowadays a large number of goods and services are offered on the
electronic market by a huge and growing number of suppliers. However,
there is still no efficient way for a customer to find a product or
information, he/she is interested in, and a supplier that can provide
it. Customers and suppliers already can not deal with so much
available information by themselves. High heterogeneity of existing
protocols, formats and underlying networks also limits development of
the electronic market.
This results in a demand for brokerage systems, which can work as
intermediary entities between customers and content suppliers.
Brokerage systems assist a customer during the trading process and
hide heterogeneity and distribution of information from the customer.
The design of domain and supplier independent generic architecture
for such brokerage systems is an objective of the project GAIA
(Generic Architecture for Information Availability). GAIA received
part-funding from the EU's ACTS programme for Research and
Technological Development. The GAIA brokerage system allows a
customer to
Blinov,Bessonov,Clissman Informational [Page 1]
- search for a particular "product" (information, content or services),
which he/she is interested in
- locate the product, i.e. find supplier(s),
from which this product is available
- order the product from the supplier
- receive delivery of the product by digital means
All these actions are carried out by the broker according to requests
of the customer. Broker services are accessible to the customer
through the unified user interface. The customer system does not have
to support all the protocols involved in the trading process.
Full specification of the GAIA Architecture is available in the GAIA
Standard [1]. The GAIA Standard includes a description of the GAIA
Reference Model, GAIA Functional Architecture, GAIA Standard Profiles
and specification of the GAIA interfaces.
This memo does not aim to include the whole text of the GAIA Standard,
but to present basic ideas and concepts of this standard.
The structure of this memo follows the structure of the GAIA Standard:
1. The GAIA Reference Model, which provides a common basis for the
description and specification of brokerage systems, including the
GAIA system.
2. The GAIA Functional Architecture, which defines functional
elements of the GAIA Broker, their roles and relationships.
3. The GAIA Brokerage System Interfaces, which describes internal and
external interfaces of the GAIA brokerage system.
4. The GAIA Standard Profiles, which specifies mandatory and optional
profiles to which brokerage systems may conform.
2. The GAIA Reference Model
The Generic Architecture for Information Availability (GAIA)
Reference Model outlines the operations and actors involved in
finding, ordering and delivering physical and digital objects and
services ("Products") in a global brokered distributed information
environment. It provides an overall view of the GAIA environment, and
illustrates the respective roles of and relationships between its
components. Further work on standards and frameworks for individual
components of the GAIA environment uses the model and terminology
provided by the Reference Model.
Blinov,Bessonov,Clissman Informational [Page 2]
The GAIA environment is a collection of actors and functions that are
combined to support a procedure for information and services
discovery, order and delivery. The actors play roles in the
procedure, including initiation and execution of the Actions which
are combined to make up the overall transaction. The GAIA
architecture provides a standardised and widely applicable framework
for the provision and implementation of the brokered search and
retrieve applications in a large-scale networked environment.
2.1. GAIA Roles
The GAIA model considers three principal roles, which can be played
by the GAIA actors. These are the Customer, the Broker and the
Supplier. These Roles are shown in the Figure 1 below. It also
considers a further class of active entities, who play supporting
roles in the Actions. This latter class is known as GAIA "Helpers"
and includes, for example, authentication and payment. The actors are
organisations and individuals in the supply chain. Every GAIA actor
plays at least one role at any given time.
2.1.1. The Customer
The aim of the Customer is to obtain some Products or information
about some Products. The Customer role initiates the GAIA transaction
by requesting one or more GAIA Actions, and receives the results of
the transaction. The Customer may deal with actors playing either of
the other two roles, the Broker or the Supplier. These actors may
themselves play the role of the Customer while requesting further
services from other Brokers.
2.1.2. The Broker
The Broker provides brokerage services to the Customer and the
Supplier. It responds to requests from the Customer to provide
Products, or information about Products. The Products that the Broker
supplies to the Customer may originate from one or more Suppliers
and/or Brokers. The Broker's primary role is to act as a collector
and collator of information from a number of different Suppliers, and
to supply this information to the Customer, thus obviating the need
for the Customer to deal with a variety of Suppliers. A Broker can
also be considered to act on behalf of a Supplier, distributing
information about the Products available. The actor playing the role
of the Broker may play the role of a Supplier to a Customer or other
Broker at the same time. The Broker may play the role of a Customer
while interacting with another Broker or with a Supplier.
Blinov,Bessonov,Clissman Informational [Page 3]
2.1.3. The Supplier
The Supplier is the source of the Product supplied to the Customer.
The Supplier provides the Broker with information about the Product
that it can supply. The Supplier may supply its Product directly to
the Customer, or to the Broker, for forwarding to the Customer. An
actor playing the role of a Supplier may also play the role of a
Broker. A Supplier may deal with a large number of Brokers and
Customers, over a number of GAIA transactions.
2.1.4. Helpers
A Helper is an application layer entity playing a supporting role in
a GAIA transaction. Helpers provide some service needed in the supply
chain, but outside the core functionality of the Broker. Examples
include a global directory service or payment service or
authentication service.
The authentication Helper is concerned with facilitating the
authentication of one actor to another.
The payment Helper is concerned with supporting a mechanism for
payment to one actor by another.
In any given GAIA transaction, there will be one or more Customers
(usually one), one or more Brokers, and one or more Suppliers. A
description of the Product sought by the Customer is provided by the
Customer to the Broker. The Broker may involve other Brokers in the
search for the Product. When a Supplier of the Product is discovered
by the Broker, this information is included in the response of the
Broker to the Customer. During the course of the Action, it may be
necessary to call upon the services of one or more Helpers.
2.2. GAIA Actions
Each GAIA transaction is made up of one or more Actions. These
Actions are requests by the Customer to the Broker or the Supplier to
carry out some operation, and to respond to the Customer. Four
Actions are defined
- Search
- Locate
- Order
- Deliver
These Actions are shown in the Figure 1.
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+--------+ . . +--------+ . . +-----------+
| |-- 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. In order to do this, the
Customer provides the Broker with some description of the Product
which it requires. On the basis of this description, the Broker
carries out a search on behalf of the Customer and returns the result
to it. The result of a Search Action is a set of unique identifiers
referencing the Products matching the description provided by the
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. In order to allow the Broker to do this, the Customer
provides an unambiguous identification of the Product, which may be
the result of a Search Action. The Broker returns information to the
Customer about a source or sources for the Product. These data
include the Terms of Availability information such as methods of
delivery available, time of delivery, costs, etc. However, this
information can not be considered final, since some special terms and
conditions may apply, e.g. discounts for some categories of
Customers. The final version of the Terms of Availability is
established during the negotiation phase of 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
Blinov,Bessonov,Clissman Informational [Page 5]
Product directly to the Customer. To enable Order, the Customer
provides the Broker/Supplier with Product source information, which
may be a result of a Locate Action. The Order Action consists of a
negotiation phase and (possibly) a purchase phase. During the
negotiations phase the Customer obtains the quotation which contains
the final version of the Terms of Availability for the (batch of)
Products he is considering purchasing. If the Customer finds these
conditions satisfactory, he commits to the purchase. Alternatively if
the Broker or Supplier supports telepresence services for the human
interaction with the Supplier or Broker representatives, these may be
used during the negotiations.
2.2.4. Deliver
The Deliver Action is carried out when the Broker provides the
Customer with some requested Product. The Product may be information,
some physical object or metadata. The Deliver Action may be in
response to an Order Action, a Search Action or a Locate Action.
While the Actions presented in this section may logically be taken to
form an integrated sequence, this is not necessarily the case.
Actions may take place independently, rather than as a 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.
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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 the components, and the manner in which
they interoperate.
In order to work in a heterogeneous environment the GAIA Functional
Architecture introduces three levels of abstract elements of the
Broker: the Kernel, Functional Unit Managers (FUMs), and Functional
Units (FUs) (see Figure 2).
GAIA Broker:
------------
[ Kernel ] Kernel
/ \ level
/ \
[Functional Unit] [Functional Unit] Technology-independent
[ Manager ] [ Manager ] action-dependent
/ \ / \ level
/ \ / \
[Functional][Functional] [Functional][Functional] Technology
[Unit ][Unit ] [Unit ][Unit ] dependent
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.
Blinov,Bessonov,Clissman Informational [Page 7]
Functional Unit Managers contain technology independent functions for
particular actions. In order to use a particular technology FUM uses
the services of attached FUs. There may be several FUs associated
with a FUM, allowing the FUM to operate in different technology
contexts. There is one FUM in the system for every area of
functionality, e.g. search, locate, order. The Kernel is responsible
for managing the activity of different FUMs (corresponding to
different actions) and synchronising events between them.
The GAIA Functional Architecture establishes relationships between
the existing technologies (standards and protocols) that are combined
in the GAIA Standard, in the context of a brokerage system. It is to
be expected that new technologies will evolve which will be viable
alternatives to those selected. The abstract and modular nature of
the Functional Architecture allows the replacement of one technology
with a new one without disruption to the rest of the brokerage
system.
3.2. Functional Units
The brokerage system provides a number of services to its users.
These services are supported by the functions of the brokerage
system. These include, for example,
- searching
- ordering
- payment
Each of these functions can be provided by a number of different
candidate technologies. However, the operations that are required to
be carried out remain the same - regardless of the selected
technologies, the functional requirements do not change. The required
operations are described in terms of abstract primitives, which can
be mapped to the protocol instructions of the technology selected to
support the function. A mapping component, called a Functional Unit
(FU), is defined for each candidate technology, and converts calls to
abstract primitives into protocol instructions. The FU acts as an
adaptor between its particular technology and the rest of the
brokerage system.
Functional Units are defined for each candidate technology that can
be used to fulfil a particular functional need of the brokerage
system. A Functional Unit accepts abstract primitive invocations, and
maps them to calls to the particular technology to which it is
dedicated. The results of these calls are translated into the
corresponding abstract primitives and returned by the FU, as shown in
the Figure 3.
Blinov,Bessonov,Clissman Informational [Page 8]
* The rest of the Broker *
^
| -abstract primitives
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. In order to
select the most appropriate FU (and technology), the brokerage system
needs to know which is the most useful at any particular time,
generally the one supported by the target Supplier system. This is
the responsibility of the Functional Unit Manager, or FUM. Each
function of the brokerage system has a single FUM, which is invoked
in terms of abstract primitives by the Broker Kernel. This FUM
selects the most appropriate of the candidate technologies, and calls
the corresponding FU (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 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.
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+--------------------------------------+
| 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.
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+-------------------------------------+
| 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 the Figure 6.
Search FUM
The Search FUM accepts requests to carry out a search for Products
that fit a particular user description. It returns lists of
identifiers of Products that fit the description.
Locate FUM
The Locate FUM accepts Product identifiers, and discovers where they
may be obtained. It returns lists of Suppliers and locations for the
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
Blinov,Bessonov,Clissman Informational [Page 11]
The GAIA Broker:
----------------
(Customer)) (Alerting)) ( DS )) (Auth)) (Payment))
( FUs )) ( FUs )) ( FUs )) ( FUs)) ( FUs ))
(e.g.HTTP)) (e.g. SMS)) (eg LDAP)) ( )) (e.g.SET))
\/ \/ \/ \/ \/
[Customer] [Alerting] [ DS ] [ Auth ] [Payment]
[ FUM ] [ FUM ] [ FUM ] [ FUM ] [ FUM ]
| | | | |
+----------------------------------------------------------+
| Broker Kernel |
+----------------------------------------------------------+
| | | | |
[ Search ] [ Locate ] [ Order ] [ Stream ] [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
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.
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
Blinov,Bessonov,Clissman Informational [Page 12]
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 internal and external interfaces of the GAIA
brokerage system.
4.1. Internal Interfaces
The definition of communications between functional components within
the GAIA Broker is based on the OMG CORBA model [2]. Interfaces
between components are defined on the IDL language, specified by OMG.
Interface calls are passed between components by 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].
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4.2. External protocols
The GAIA Broker can use existing protocols to communicate with other
actors. For example, it can use HTTP for interactions with Customers,
Z39.50 for search, etc. As described in the GAIA Functional
Architecture, support of particular technologies is provided by FUs.
A set of supported protocols can be extended by attaching
corresponding new FUs to a Broker. The GAIA Broker can support
several protocols for each action. FUMs will select the most
appropriate protocol for a transaction. The more protocols are
supported by the Broker, the better service it can provide to
Customers and Suppliers.
The GAIA Standard does not limit the set of protocols supported by
the Broker. However, for the purpose of interoperability, it
specifies several GAIA profiles. These profiles aim to define the
common subset of protocols (and a common range of protocol
parameters), which is encouraged to be supported by Brokers in order
to make possible communications between GAIA Brokers and with GAIA-
aware Suppliers and Customers.
Existing protocols are not the only way to contact the GAIA Broker.
The GAIA interfaces have been designed as a generalisation of
existing interfaces and protocols, so they provide more functionality
than any particular protocol. In order to give access to full
functionality of the GAIA Broker, the GAIA Standard allows users
(Customers and other Brokers) to use directly the CORBA-defined
Customer interface of the GAIA Broker (interface between Customer FUM
and FUs) as shown in Figure 7. In this case the Customer system gets
access to the Customer interface of the Broker using the service of
an underlying ORB, and can request operations by calling
corresponding methods of the interface. 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 avoiding convergence between a particular protocol
and the GAIA interface. The former way makes possible interactions
with all existing types of Customer and Suppliers, using existing and
widespread protocols. The later way has been designed to archieve
maximum functionality by using native GAIA methods for communications
with Customers and Suppliers.
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+----------------+
|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 which a Broker provides to a Customer,
and the greater the length of the supply chain which the Broker
wishes to support, the more advanced the profile, and/or the greater
the number of extension modules the Broker must support.
5.1. Supply Chains
The GAIA profile definition approach is based on the possible types
of supply chains, which 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 inter-broker operations take place at other points in the
chain. The supply chain may take a number of different forms:
Blinov,Bessonov,Clissman Informational [Page 15]
- a minimal chain, where the Customer and the Broker are the ends of
the chain, and there are no intervening links. In this case, the
Broker plays the role of Supplier to the Customer.
- a three-piece chain, where the Broker deals with the Customer and
the Supplier, but not with any other Broker.
- a longer chain, with one or more inter-broker operations.
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, and 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 their
turn propagate the request, if they cannot fulfil it.
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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, in order to take part in
inter-broker communications, the Basic profile is recommended. For
interaction with non-CORBA-aware entities, and for the use of
advanced services, there are other modules of the standard to which
the Broker may conform. These are denoted "Extension Modules", and
they characterise the protocols and standards in a particular area of
functionality. A Broker can choose an appropriate set of Extension
Modules to conform to according to 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, which is more important in its area of
operation, and implement interfaces defined in these modules. These
interfaces are important only inside the broker system and do not
play any role in communication with other GAIA actors. However, a
declaration of supported interfaces is important for the
Blinov,Bessonov,Clissman Informational [Page 17]
administrator to find in which areas 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 [5]. It means that a Customer should be able
to access the basic functionality of the GAIA Broker by using an HTTP
1.1 and HTML 2.0 -conformant web-browser.
It should be possible for Customers to locate a GAIA Broker. Thus a
GAIA Broker should be registered in a Directory Service using a
schema specified in the GAIA Standard [1].
+-------------------------------------------------+
| Minimal Profile |
+------------------------+------------------------+
| Customer | HTTP 1.1 (server), |
| | HTML 2.0 |
+------------------------+------------------------+
5.4. 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
Blinov,Bessonov,Clissman Informational [Page 18]
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
Blinov,Bessonov,Clissman Informational [Page 19]
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.
Blinov,Bessonov,Clissman Informational [Page 20]
+-------------------------------------------------+
| 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 requires the GAIA Broker also
to be able to accept and to generate e-mail messages. The e-mail
protocol specified is Internet e-mail, based on SMTP protocol [8] and
mail data formats specified in RFC 822 [9]. This protocol is
sufficient for the creation, transmission and management of textual
e-mail messages. However, for the transmission of data files of
various types, extensions to the SMTP/RFC822 protocols are required.
The mail extensions specified by the 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,Bessonov,Clissman Informational [Page 21]
+--------------------------------------------------------+
| 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, so
this scenario is out of scope of this standard.
- from a Supplier to a Customer via a Broker
The Broker can add value to the stream delivery process by
implementing cache algorithms, mixing streams, branching one stream
to several Customers, etc.
- from a Broker to a Customer
The Broker can keep a small amount of multimedia data (e.g., audio
examples) in its own database and deliver it to a Customer upon
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 to support full behaviour of RTP
application service entity ("translator" or "mixer") but it is not
Blinov,Bessonov,Clissman Informational [Page 22]
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 the
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), authentication of senders
and receivers in network transactions, as well as the
authentication of documents. Authentication is required for three
situations: authentication at the user workstation when starting
the session, authentication in a local environment (client/server
authentication) and authentication in a global, open network
(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.
Blinov,Bessonov,Clissman Informational [Page 23]
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 for a Broker to support SET
v1.0 merchant's server and SET certification protocol, specified in
[18].
Blinov,Bessonov,Clissman Informational [Page 24]
+----------------------------------------------------+
| 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.
Blinov,Bessonov,Clissman Informational [Page 25]
+----------------------------------------------------+
| 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, which is 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 very lively discussion and their valuable direct and
indirect input in the process of design of the GAIA Standard.
Blinov,Bessonov,Clissman Informational [Page 26]
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., Berners-Lee,
T., "Hypertext Transfer Protocol -- HTTP/1.1", RFC 2068, January
1997.
[4] Berners-Lee, T., Connolly, D., "Hypertext Markup Language -
2.0", RFC 1866, November 1995.
[5] ANSI/NISO Z39.50-1995 or ISO 23950 "Information Retrieval:
Application Service Definition and Protocol Specification".
[6] ISO 10161:1997 "Information and documentation -- Open Systems
Interconnection -- Interlibrary Loan Application Protocol
Specification".
[7] Postel, J., Reynolds, J.K., "File Transfer Protocol", RFC 959,
October 1985.
[8] Postel, J., "Simple Mail Transfer Protocol", RFC 821, August
1982.
[9] Crocker, D., "Standard for the format of ARPA Internet text
messages", RFC 822, August 1982.
[10] Freed, N., and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message Bodies",
RFC 2045, November 1996.
Freed, N., and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046, November
1996.
Moore, K., "MIME (Multipurpose Internet Mail Extensions) Part
Three: Message Header Extensions for Non-ASCII Text", RFC 2047,
November 1996.
Blinov,Bessonov,Clissman Informational [Page 27]
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, Audio-Video Transport Working Group, January 1996.
[13] Hoffman, D., Fernando, G., Goyal, V., Civanlar, M., "RTP Payload
Format for MPEG1/MPEG2 Video", RFC 2250, January 1998.
[14] Freier, A., Karlton, P., Kocher, P., "The SSL Protocol - Version
3.0", INTERNET-DRAFT, Transport Layer Security Working Group,
November 1996,
See <http://home.netscape.com/eng/ssl3/index.html>.
[15] PKCS #7: Cryptographic Message Syntax Standard. Version 1.5,
November 1993.
[16] Linn, J., "Generic Security Service Application Program
Interface", RFC 1508, Geer Zolot Associate, September 1993.
[17] Public-Key Infrastructure (X.509) IETF Working Group,
<http://www.ietf.org/html.charters/pkix-charter.html>, July 98.
[18] "SET Secure Electronic Transaction Specification", Version 1.0,
MasterCard and Visa, May 97.
[19] Digital Cellular Telecommunications System (Phase 2+): Technical
Realization of the Short Message Service (SMS) Point-to-Point
(PP) (GSM 3.40). Version 5.2.0. European Telecommunications
Standards Institute. May 1996.
Blinov,Bessonov,Clissman Informational [Page 28]
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 (1998). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
Blinov,Bessonov,Clissman Informational [Page 29]
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,Bessonov,Clissman Informational [Page 30]
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