| The Grid is a set of technologies that, when deployed across
an enterprise's resources, ease the creation of applications and infrastructure
that facilitate collaborative and
adaptive systems.1 In this article, we
will explore the vital role that standards play in establishing the Grid. We
also discuss the important role played by open software, in particular
the software developed within the Globus Alliance, a collaboration of
researchers, system architects, and software developers that has been pursuing
this goal for several years.
Developers of Grid systems can build on a range of established
and proposed standards that have emerged from work on the Internet, the
World Wide Web, and Web-based applications—technologies that, like the
Grid, seek to support resource sharing and collaboration. However, a number
of key capabilities must be added before interoperable Grids can be
constructed. Much work is currently underway to develop specifications,
implement solutions, and propose standards (or additions to existing standards)
for Grid computing. A particular focus of these efforts is system monitoring
and management, an area that has not seen the broad adoption of
standard solutions analogous to the Internet and the World Wide
Web.2 This area has instead seen an abundance
of proprietary systems and specifications without any particular set of
solutions becoming dominant.
The Work of the Globus Alliance
Figure 1. The Globus Alliance employs an iterative design methodology for the development and evaluation of proposed Grid technologies.
Our work in the Globus Alliance has historically consisted of
the following activities, each of which represents a key challenge in
the establishment of a useful Grid.
- Identifying and refining our understanding of the
fundamental problems shared by potential users of the Grid (those who
would develop or use Grid-based applications)
- Developing and refining solutions (including both specifications
and implementations) to these fundamental problems
- Applying these solutions to real problems in order to test
their applicability
- Proposing and championing these solutions as standards in
broader communities
- Expanding availability (implementations and support) and
adoption (uses in many settings) for these standard solutions
Our approach to realizing the Grid vision creates an ongoing
tension between the short-term (but ongoing) need to have working software
that supports user requirements and the longer-term need to formulate
and promote new solutions that "push the envelope" of capabilities. In these
early stages of the "Grid era"—when research is ongoing and
constantly changing—this tension is quite
strong: the solutions are evolving quickly enough that working
implementations cannot keep up without making some sacrifices in continuity and
backwards-compatibility. Our challenge is to find
a good balance that serves both needs reasonably well.
Another challenge faced by the Globus Alliance (and the
Grid community at large) is the need to formulate its solutions and standards
in ways that appeal to the larger IT industry and the market it
serves. Failure to meet this challenge would result in Grid computing languishing
as a niche market, almost certainly without the critical mass required
to sustain itself over time. Until standard Grid solutions are incorporated
into mass market infrastructure technologies (as the Internet and the Web
have been integrated into every major computer system now sold—not
to mention cellular telephones, televisions, automobiles, and
other commodity products), the Grid will remain beyond the reach of most of
the users it is intended to help.
The Importance of Standards
The Grid vision requires protocols (and interfaces and policies) that
are not only open and general-purpose but also
standard. Indeed, we would argue that "Grids will be standards-based
or not at all." It is standardization that allows potential collaborators
to establish resource-sharing arrangements quickly and easily with
any interested party. It is standardization that will allow organizations
to establish resource-sharing contracts routinely for acquiring resources
on demand, thus avoiding the need to build expensive data centers
designed to handle peak loads that remain underutilized most of the
time. Standard solutions can allow us to move away from today's plethora
of balkanized, incompatible, non-interoperable distributed systems
and toward a model where computing and data capabilities are available
as standardized, interchangeable commodities.
The World Wide Web Consortium (W3C) has been highly successful
at promoting a number of proposed standards in various stages
of development that are commonly referred to as the "Web
services" specifications.3 The bases for
these standards are the HTTP protocol, the XML encoding format, the
SOAP remote procedure call mechanism, and the WSDL language. Web
services standards have already been adopted by every major provider in the IT
industry, and it is clear that they are heading toward a long life and a
ubiquitous presence in current and future IT systems.
While Web services standards meet many needs in industry and are
highly popular, there are currently no established Web services standards
for the interfaces used to manage, monitor, and interact with resources and
with services that maintain persistent state. Thus, it is not possible to define
tools that monitor, manage, troubleshoot, etc., diverse resources in
standard ways: critical issues if one is to build large-scale systems. It is precisely
these issues with which Grid computing is concerned.
Our current strategy, therefore, is to ensure the establishment of
Web services-based standards in these areas, and the Globus Alliance's efforts
are currently focused on contributing significantly to this work. Our goal is
a convergence of new and existing Web services standards with the
solutions developed by the Grid community. A further goal is the standardization
of the resulting technology so that it becomes at least as accessible
as current Web services technology.
Accomplishments
Standards organizations with which we are working to
formalize specifications for the Grid include the Global Grid Forum
(GGF)4, the World Wide Web Consortium (W3C),
the Organization for the Advancement of Structured Information
Standards (OASIS)5, and the Internet
Engineering Task Force (IETF).6
The Global Grid Forum has played a key role in developing
and articulating the Open Grid Services Architecture (OGSA), which
defines the Grid community's "guiding principles" for Web
services/Grid convergence.7 The GGF Open
Grid Service Infrastructure (OGSI) Working Group formalized the OGSI
v1.0 specification in 2003, which was our first attempt to define Web
services standards for Grid computing.8
The open source Globus Toolkit®
3.0 (released in mid-2003) contained the first OGSI implementation and
was followed soon after by a number of independent implementations
(see sidebar).9
We were disappointed (but not surprised) to learn subsequently
that the Web services community was not satisfied with OGSI v1.0, due largely
to a belief that OGSI v1.0 did not fit well enough with existing Web
services architectural principles. In late 2003 and early 2004, a smaller group of
Grid and Web services architects (leaders in their respective fields) met
intensively to work out a compromise set of specifications, which was announced
at the GlobusWORLD 2004 conference in January 2004. This set
of specifications is known collectively as the Web Services Resource
Framework, or WSRF.10 It is our belief, expressed by leaders of both the
Web services and Grid communities, that WSRF is the much-desired
convergence of Web services and Grid technologies and that it will lead to
a body of widely-available, highly-interoperable Grid technology.
Of course, work to finalize the now-drafted WSRF specifications and to gain formal acceptance and
endorsement by one or more standards bodies is yet to be done. The Globus
Toolkit 4.0, expected in mid-2004, will include a WSRF implementation.
While WSRF is undoubtedly a major milestone in the Grid's history,
it is nevertheless only one of many standards-related activities
undertaken by the Grid community and by the Globus Alliance. The IETF
recently approved our X.509 Proxy Certificate Profile as a proposed standard.
This action standardizes the format of the Grid "proxy" certificates used
to support the Grid's essential single sign-on and delegation capabilities.
The GGF recently accepted our specification of the GridFTP v1.0 protocol
for high-bandwidth data transfer over wide area networks.
We have also been working in the Grid and Web services
communities toward draft specifications for Data Access and Integration (DAI) in
the GGF, a WS-Agreement specification in the W3C for establishing
service agreements between service providers and consumers (e.g., reserved
network bandwidth or compute node scheduling priorities), and replica
location capabilities for data management systems. We have actively
engaged ongoing standards work in other areas, making Grid-focused contributions
to the development of the WSDL 2.0 (Web Service Description
Language) specification, the WSDM (distributed web service management)
specification, and the SAML (Security Assertion Markup Language - an
XML-based framework for exchanging security
information) and XACML (Extensible Access Control Markup Language -
an XML specification for expressing policies for information access over
the Internet) languages for encoding policy specifications.
Figure 2. The Web Services Resource Framework provides a layer of
commonality for all Grid Services based on the Web services model.
Conclusions and Invitations
In our view, the definition and widespread adoption of
standard protocols and interfaces is currently the single most critical problem facing
the Grid community. Fortunately, we are making good progress. On
the standards side, we have the increasingly effective
Global Grid Forum and representation in other IT
standards organizations. We have broadly-endorsed efforts underway to
define OGSA and WSRF, which enshrine Grid technology within the
highly-successful Web services suite of products and solutions.
On the implementation side, seven years of experience and
refinement have produced a widely used de
facto standard, the open source Globus Toolkit.
IBM, Microsoft, Platform, HP, Sun, Avaki, Entropia,
United Devices, and other IT industry members have expressed strong support for
OGSA and announced their own products and services based on OGSA standards.
In time, we will be able to state that for an entity to be part of
the Grid it must implement OGSA protocols
and interfaces, just as to be part of the Internet an entity must speak
IP (among other things). Both open source and commercial products
will interoperate effectively in this heterogeneous, multi-vendor
Grid world, thus providing the pervasive infrastructure needed to
support compelling Grid applications.
Establishing the Grid and the standards that define it is still
very much a "work in progress." Because we are taking a
standards-based approach to the problem, it is open
to input from many sources. The standards organizations (GGF,
W3C, OASIS, IETF) all have open memberships, allowing
organizations and individuals to become
contributors to their work. The Globus Alliance
also welcomes new partners in our broad mission to realize the Grid
vision through the Globus Alliance Affiliates program (for academic and
R&D members) and the Globus Alliance Commercial Affiliates program
(for corporate participation). See www.globus.org for details.
References
1 I. Foster. What is the Grid? A Three
Point Checklist. GRIDToday, July 20, 2002.
2 I. Foster, C. Kesselman, S. Tuecke. The Anatomy of the Grid: Enabling
Scalable Virtual Organizations. International
J. Supercomputer Applications, 15(3), 2001.
3 World Wide Web Consortium (W3C),
http://www.w3.org/. The W3C's activities with respect to Web services are detailed
at http://www.w3.org/2002/ws/.
4 Global Grid Forum,
http://www.grid-forum.org/.
5 Organization for the Advancement of Structured Information Standards
(OASIS), http://www.oasis-open.org/.
6 Internet Engineering Task Force (IETF),
http://www.ietf.org/.
7 I. Foster, C. Kesselman, J. Nick, S.
Tuecke. The Physiology of the Grid: An Open Grid Services Architecture for
Distributed Systems Integration. Open Grid Service Infrastructure WG, Global Grid
Forum, June 22, 2002.
8 S. Tuecke, K. Czajkowski, I. Foster, J. Frey, S. Graham, C. Kesselman,
T. Maguire, T. Sandholm, P. Vanderbilt, D. Snelling. Open Grid Services
Infrastructure (OGSI) Version 1.0. Global Grid
Forum Draft Recommendation, 6/27/2003.
9 The Globus Toolkit software is described in detail and available for download
at http://www-unix.globus.org/toolkit/. Globus Toolkit is a registered trademark held
by the University of Chicago.
10 WSRF status and activities are described
in detail at http://www.globus.org/wsrf/.
About the Authors
Lee Liming is the Manager of the Distributed Systems Laboratory
at Argonne National Laboratory, the "Chicago home" of the
Globus Alliance. His work with Ian Foster, Carl Kesselman, and Steve Tuecke
on Grid computing began in 1999, and he is currently responsible for
work resulting in the Globus Toolkit and related Grid technologies. Through
his work at Argonne National Laboratory, Mr. Liming is engaged in a broad
range of Grid deployment and application projects including NEESgrid, the
NSF Middeware Initiative/GRIDS Center, the NASA Information Power
Grid, and the National Computational Science Alliance. He was previously
a product manager and software engineer at ProQuest Information and
Learning and an IT manager at the University of Michigan's School of Information.
Having joined the Mathematics and Computer Science Division of
Argonne National Laboratory in 1989 as a postdoctoral researcher,
Ian Foster has risen to the rank of senior scientist
and associate division director. Since 1996, he has held a joint appointment in
the department of computer science at the University of Chicago, where he
now has the rank of professor. His research specifically addresses
scalable authentication and authorization technologies (the Grid
Security Infrastructure), information discovery and dissemination (the Meta
Directory Service), resource reservation and management, high-performance
data transfer, and data replication. He directs the Argonne Distributed Systems Laboratory, which designs
and develops the Globus Toolkit and standards on which it is based.
The toolkit has been adopted as the central component in Grid solutions offered
by IBM, HP, Oracle and other major IT companies.
Author Contact Information
Lee Liming
Argonne National Laboratory
E-mail: liming@mcs.anl.gov
Ian T. Foster
Argonne National Laboratory
E-mail: foster@mcs.anl.gov | 
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