Services and Consulting, Inc.
Scaling Object Service Architectures to the Internet
September 28, 1998
Principal Investigator: Craig
Bannon, Gil Hansen, Frank
Manola, Mark Palmer,
Paul Pazandak, and Venu
contract: DAAL01-95-C-0112, AO C366
September 29, 1995 - September 28, 1998
OBJS Document: http://www.objs.com/OSA/Final-Report.html
Web technology and distributed object technology need to be better integrated
to realize the benefits of both. The Web is already moving beyond documents
to provide distributed applications. Without an architectural framework,
the web environment will build services parallel to but different from
the object middleware community, and enterprise architects will be forced
to make idiosyncratic tradeoffs in constructing systems that need to use
both architectures together.
The overall thesis of our project is that an Internet Services Architecture
(ISA) can help to unify both Web and ORB architectures. During the
life of the project, we developed the broad outline for a general ISA architecture
and explored its utility in the virtual office and command and control
domains. We then focused on an instantiation of the general ISA which
we call an Intermediary Architecture (IA), which provides a new
family of ways to add middleware services into Web architectures by inserting
component middleware between Web client and server. We constructed
a series of prototypes to demonstrate parts of the IA architecture.
Object Services Architectures (OSAs) are distributed
software backplanes with plug-in component object services. OSAs
promise vast improvements over conventional stovepipe software architectures
in reducing software life cycle costs and providing modular software design.
The Object Management Group (OMG) Object
Management Architecture (OMA) (partly based on our previous DARPA
research) is an important OSA because it is backed by a consortium of over
800 companies, is developed by an open process, and is being adopted into
large-scale industry and DoD enterprise-critical systems and standards
profiles including DoD AITS-JTF/ATD, NIMA, DMSO HLA, and DII COE.
Today the Web consists of thin clients, which provide
universal browser interfaces, and web servers, which provide back-end access
to global information resources (that's where the data is). Meanwhile
OSAs provide access to suites of middleware services (that's where the
system management and application extensibility mechanisms are).
As important as OSAs are becoming, they are a new kind of software architecture
and industry still lacks theory and experience in scaling OSA systems to
levels to support large-scale, world wide operations like command and control.
At present, OSAs are not well connected to control
access to web data sources. Without better integration, the web community
will build protocol extensions (e.g., W3C WEBDAV) parallel to but different
than the OSA community, and enterprise architects will be forced to make
idiosyncratic tradeoffs in constructing systems that need to use both architectures
together. Furthermore, even if we can unify these two
sorts of architectures, there is still a question of what new Internet
services might be useful that are not already identified by OMG, how to
compose these, and how to federate them in large WAN environments (many
of these questions are still unanswered for pure ORB architectures).
Another problem is the kind of object model that is appropriate for both
Web and ORB. Finally, there is the problem of how enterprises can
deal with the incredibly complex Internet environment where technologies
There is a family of architectures for composing
ORBs and the Web. Together, these architectures open up a wide new
spectrum of services and facilities that can enable a broad class of future
architectures. We call this class of architectures an Internet
Services Architecture (ISA) by analogy
with the OMG Object Services Architecture. The overall thesis
of our project is that an Internet Services Architecture can help to unify
both Web and ORB architectures. Some approaches for
instantiating ISA architectures are already known (developed over the last
three years): e.g., the three tier architecture where Web servers
access ORBs via CGI scripts; the approach pioneered by Visigenic and Netscape
of downloading an ORB client via an applet; and the recent W3C HTTP-NG
project where HTTP is re-implemented on a distributed object backplane.
Our project focused on another variant ISA that appears to be broadly useful,
which we called an Intermediary Architecture because it inserts middleware
services between Web client and server.
In this section, we divide our main technical accomplishments
into three layers of description corresponding roughly to the three years
of the contract.
Internet Tools Survey and the Virtual Office
In FY96 we organized Object Services and Consulting,
Inc. (OBJS) as a virtual office (distributed
office), dependent on Internet, Web, database, distributed object, and
related infrastructure technologies. Our main focus that year was
on identifying, describing, and installing a large family of software that
constitutes the core of Internet, Web, and distributed object technology
for virtual enterprise computing. A main contribution that year was
the Internet Tools Survey, described in the
Technology Transition section below.
The Internet Tools Survey provided a detailed look at many technologies
needed to Internet-enable applications but that so far did not clearly
fit into an overarching software architecture and were then beyond the
realm of OMG middleware concern. To change that situation, we began
to move OMG in the direction of a rendezvous with Internet and Web technologies
by co-chairing the OMG Internet Special Interest
Internet Services Architecture (ISA)
In FY97 we worked with OMG to develop a high level
industry roadmap for an Internet Services Architecture
to unify both Web and ORB architectures. The ISA consists of
a suite of possible standards that OMG might adopt over a several year
period to make Web-ORB integration easier. The ISA extends
the OMG OMA and draws on the strengths of both OSA and Web technologies.
OSAs can provide the web with a principled model for composing object services,
federating like services with possibly varying policies and implementations,
combining these into systems of systems, and controlling binding times
of these services so new services can be added to existing systems. Both
the OMG and Web communities have sufficient momentum that neither can change
instantaneously, making an evolutionary approach the only one with a likelihood
Intermediary Architecture (IA)
In FY97 and FY98 our work focused on a specific
instantiation of the Internet Services Architecture that we call an Intermediary
Architecture. The IA splices ORB (or DCOM or other) componentware
services in between Web clients and servers to provide a management layer
that extensibly allows many new kinds of services to be plugged in.
The Intermediary Architecture is open and flexible
and can be used for many purposes including security, versioning, internationalization,
query augmentors, shielded pages, rating systems, rerouting, filtering,
logging, system management instrumentation, clocking, micropayments, disconnected,
intermittent access, tracking URL usage patterns of a community of interest,
background indexing of pages you have seen before so you can find them
again, indexing streams of audio or video, translingual translation service,
closed caption in multiple languages, and augmenting a web page with voice
access to URLs. This makes the Intermediary Architecture an excellent
candidate integration harness for testing other DARPA technologies.
Advantages of the Intermediary Architecture are:
The Intermediary Architecture is shown in the above
figure. In its simplest form, it consists of:
it provides a new kind of plug-in and an improved
way for third-parties to build extensible web applications;
it is non-intrusive requiring no change to existing
* we did not find this to be 100% true.
it generalizes many special-purpose efforts to add
specific services to Web applications;
it provides a general framework for reasoning about
how to federate and scale Web applications.
The architecture can appear in many variations:
an intermediary, also known as an interceptor,
that inserts (and composes) service behaviors
one or more service behaviors
metadata associated with services (stored
in a persistent metadata repository) as well as policy management
a management function for querying, viewing
and manipulating metadata and controls
The overall claim is that the Intermediary Architecture
provides a framework for service insertion, composition, and federation.
We do not claim to have thoroughly explored this space. There is
still much we do not understand though limited prototyping has taught us
a fair amount about the Intermediary Architecture.
there are many kinds of services that can be inserted
via an intermediary -- see the list above.
there can be more than one intermediary and different
roles can control different intermediaries. For instance, different
groups in an organization could manage security, caching, filtering, system
management and logging, functions like annotation, the ability to add new
intermediaries can be implemented as adjunct to the
client or to the server or somewhere in between. We can talk about
client intermediaries, server intermediaries, and proxy intermediaries.
more than one service can be inserted via intermediaries.
Services can compose in series or in parallel. In general, the area
of service composition needs more work since there are many ways to wire
up even two services (see lessons learned on the Network Performance
Management project where it is possible to capture performance for
just user-specified URLs or all gifs as well).
services can be inserted dynamically at run-time.
One way to do this is via a Trader that provides service discovery.
The trader can do this once at the beginning or can be continuously polling
to locate new or better service providers or to make the system more robust
if some providers fail.
a given service can store metadata it collects in
some repository. If local to the Web client, the service might provide
personal services (e.g., personal Web annotations -- see the Annotation
Service below). If shared in a group, the service can provide group
services (e.g., group annotations). If shared within a community
or on the server it can provide public or community services.
repositories could be federated together to allow
repositories can be different for different services
or they could be shared across services (e.g., so that both the performance
monitor and the annotations services could share one repository).
it is important to be able to view and query the
federation can appear in many places within this
architecture: individual services can be federated, repositories
can be federated.
To learn about the properties of the Intermediary
Architecture, we completed a series of separate prototypes of parts of
the architecture (each is separately described):
Prototyping involved reuse of a number of state-of-the-art
commercial and experimental tools including ORB systems, Web systems like
W3C Jigsaw, object DBMSs, and query systems.
Architecture Interceptor- this mechanism is installed at insertion
points to provide a way to plug object service components and before-after
filters into the communication path between Web client and Web server to
enable the installation of new services.
Object Model - this project examined how XML, DOM, PIC-NG, Dublin
Core, LORE, OMG IDL, Java, and other information and metadata representations
can add object model capabilities to the web. An associated prototype is
XML to Java
Translator - this mechanism provides an easy way to deserialize
XML DTD schemas into Java classes and is likely to be widely useful stand-alone.
Service - this prototype shows how to use the Intermediary Architecture
to plug in a service that downloads annotations on a document, providing
a way for third parties to augment web content. Different architectures
for the service could yield private, group, or public annotations and voting
or rating mechanisms.
Network Performance Monitor Service - this project shows how to
use the Intermediary Architecture to provide network performance and trend
data when accessing remote sites. This data can be used as a basis
for QoS negotiation in higher level tools.
Query Interface - this project focused on how to use an existing
natural language query system to access metadata stored in IA metadata
Service - this project provides two matchmaking services for service
discovery. One implementation is scalable and based on Internet search
engine; the other shows how to extend an OMG trader to locate Web resources.
Lessons we learned about the Internet Services Architecture
and the Intermediary Architecture were fed back to industry and DoD through
our active participation in architecture initiatives, principally the Object
Management Group (OMG), the World Wide Web Consortium (W3C), DARPA/ISO
Advanced Information Technology Services (AITS) , DARPA Dynamic Database
Panel II, the National Industrial Information Infrastructure Protocols
(NIIIP) Consortium, MCC Object Infrastructure Project (OIP), and X3H7/ODP
as described below.
The following reports were completed under this
contract. All appear on the OBJS public web page to better disseminate
the results. See OBJS
Technical Reports and Publications. Several were presented
in workshops, conferences, or journals or at standards meetings where they
were used to build consensus for an Internet Services Architecture.
and DoD C4I and Doctrine Application Domains
We identified two broad domains in which to develop
application scenarios that would use ISA technologies: virtual office
and command and control. Both domains require technology support
for collaboration-at-a-distance. We organized Object Services and
Consulting, Inc. as a fully geographically distributed virtual office environment,
making us our own testbed for collaborationware. We documented
virtual office and collaboration technology requirements and "lessons learned"
in provisioning our own virtual office domain. We
identified DoD doctrine as a good domain for future application scenarios
in command and control. We are not aware of much DARPA work in this
area though DoD has spent a substantial effort working to document its
Internet Tools Survey
Office White Paper, Craig Thompson, Shaun
Joseph, January 1997
Technologies for the Virtual Office, Frank Manola, January 1997
for Collaboration and Decision Making in OBJS, David Wells, January
Use of COTS Tools in the OBJS Virtual Office, Frank Manola, May
Office and C4I Scenarios, Frank Manola, January 1997
Defense Information Infrastructure Common Operating
Environment (DII COE) is a suite of standards that DoD enterprises build
on, but it does not contain as much information on Internet technologies
as is needed to Internat-enable future DoD applications. Mostly in
the first year of our contract, we assembled a complementary Internet
Tools Survey to provide a description of key technologies we feel must
be understood to Internet-enable enterprises, virtual offices, and command
and control. New additions after the first year include work on
web object models, web-ORB integration architectures, and traders.
Objects and the Web
Glossary, Craig Thompson, Frank Manola, January 1997
Engineering Task Force Overview, Craig Thompson, April 1996
Group Overview, Craig Thompson, April 1996, updated July 1997
Models, Craig Thompson, April 1996
for OO + Web Integration, Craig Thompson, January 1997
Web Architecture, Craig Thompson, Gil Hansen, January 1997
Languages, Steve Ford, David Wells, Nancy Wells, January 1997.
This paper was the cover story for the first
issue of WebApps magazine, a new journal edited by the World Wide
Web Consortium (W3C).
Web + DBMS
Integration, Craig Thompson, Paul Pazandak, January 1997
+ Object Integration, Gil Hansen, Craig Thompson, January 1997
a Web Object Model. Frank Manola, January 1998.
Web Object Model Construction Technologies, Frank
Manola, September, 1998.
Object Models, Frank Manola, presentation
to OMG Internet SIG, September 1998
OMG Traders to handle Service Composition,
Venu Vasudevan, September 1998
File Systems, Paul Pazandak, Venu Vasudevan, January 1997
David Wells, April 1996
Service, Gil Hansen, January 1997
Managing and Using Information
Systems and WWW Browsers, David Wells, April 1996
Tools, David Wells, April 1996
and Indexing, David Wells, Ansu Kurien, April 1996
& Collaboration Support, David Wells, Ansu Kurien, April 1996
Steve Ford, April 1996
We published the following papers:
Programming Languages, Steve Ford, David Wells, Nancy Wells, January
1997. Cover story for the first issue of WebApps magazine,
a new journal edited by the World Wide Web Consortium (W3C).
Architecture submitted to ACM Computing Surveys,
Special Issue on IC&V, for publication in 1999.
a Richer Web Object Model. Frank Manola, SIGMOD Record, Volume
27, Number 1, March 1998.
for a Web Object Model. Frank Manola, to appear as lead article
in the Special Issue on Web Object Models, IEEE Internet Computing,
Web Annotation: Promises and Pitfalls of Web Infrastructure, Venu
Vasudevan and Mark Palmer, to appear in the 32nd Hawaii International Conference
on Systems Sciences, January 1999.
We organized two industry workshops:
We co-organized the Joint
W3C-OMG Workshop on Distributed Objects and Mobile Code held in
Boston in 1996. The workshop convened some of the key players interested
in making Web + Object integration a reality.
We organized the OMG-DARPA
Workshop on Compositional Architectures held in Monterey, California,
in January, 1998. The workshop convened key players from industry,
universities, OMG, and DARPA to discuss scaling and other properties of
component software architectures and how to splice web and ORB architectures
together. We contributed papers on
We edited the Workshop
Report, which was published in ACM SIGSOFT Software Engineering
OMG. We provided overall
leadership in OMG to transition the Internet Services Architecture vision
to industry. These technology transfer efforts leveraged our project's
technical work by providing a broad forum to test our ideas, one that will
materially influence industry directions. At the same time, these
forums provide critiquing of our idea base by industry experts and acceleration
of acceptance of our architectural proposals. They also provide forums
for showcasing related DARPA technologies to industry and universities.
NCITS X3H7. We completed the primary work item
of former ANSI X3H7, which developed a feature matrix to compare object
models to show the kinds of interoperation problems that will be experienced
when different communities adopt different base object models. See
(formerly X3H7) Object Model Features Matrix, Frank Manola (Editor),
Reference Model, OMG
Core Object Model, OMG
CORBA IDL, ODMG, EXPRESS,
Open Distributed Processing
(ISO/IEC JTC1/SC21/WG7), Management
Information Model (ISO/IEC JTC1/SC21/WG4), SQL3
(H2), Matisse, C++
(J16), OO COBOL (J4),
Smalltalk (J20), Eiffel,
Object Model (SOM), OLE
Component Object Model, Analysis
and Design Methods
We are active in X3H7/X3T3-ODP working on object
models and enterprise languages.
W3C. We joined W3C and closely followed
the submission process, which resulted in our papers
on Web Object Models listed above in the Internet Tools Survey.
IETF. We participated in an IETF meeting
in December 1995 to discuss how OMG and IETF should liaison, and sent OMG
a memo on OMG-IETF
Related Technology Transfer Projects. We
provided OSA componentware architecture expertise to DARPA and industry
We participated in annual IC&V and I*3/BADD PI meetings
and project reviews throughout the life of the project.
We succeeded in advancing the state-of-the-art and the state-of-practice
in several ways during the life of the project. Our main contributions
It is still too early to tell if we will be successful in having provided
a widely useful architecture for web-object integration, but, if so, we
will have helped provide "objects for the masses" in the form of an understandable
abstract framework for scaling, composing, and federating services to enable
rapid application development.
We developed a new software architecture for Web-ORB integration which
we call an Intermediary Architecture because it inserts middleware
services between Web client and server. We extensively reviewed
the Web-ORB integration architecture literature and, until recently, found
little other work on extending the web with intermediaries though there
is prior work on Web proxies for use in firewalls and for caching and ORB
interceptors for security. We developed prototypes to show how useful
this intermediary architecture is and that it provides a generally useful
approach for connecting Web and ORB architectures. Lessons learned
include the fact that today's web clients are not open enough to directly
support this architecture but a universal intermediary could provide this
openness in a portable manner.
The particular prototypes we developed (interceptors, annotations, network
performance monitoring, query interface, trader) and the web object model
all provide insights into the general architecture and at the same time
are interesting and useful in their own right.
Our work on virtual office scenarios is one of the best documented examples
of how to use Internet-based technologies to build small business virtual
Our architecture and technology transfer activities are making a direct
impact on OMG Object Management Architecture and OMG's platform technology
roadmap as well as directly benefiting a number of DARPA and industry initiatives:
DARPA AITS (ISO) Architecture, NIIIP, and MCC OIP.
This research is sponsored by the Defense Advanced Research
Projects Agency and managed by the U.S. Army Research Laboratory under
contract DAAL01-95-C-0112. The views and conclusions contained in this
document are those of the authors and should not be interpreted as necessarily
representing the official policies, either expressed or implied of the
Defense Advanced Research Projects Agency, U.S. Army Research Laboratory,
or the United States Government.
© Copyright 1996-1998. Object Services and
Consulting, Inc. Permission is granted to copy this document provided
this copyright statement is retained in all copies. Disclaimer: OBJS does
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