Thoughts on OMA-NG:

The Next Generation Object Management Architecture

Craig Thompson
Object Services and Consulting, Inc.
Ted Linden and Bob Filman
Microelectronics and Computer Technology Corporation (MCC)
 

Abstract:  The OMG Object Management Architecture (OMA) has proven to be a successful foundation for achieving distributed, interoperable systems. However, the OMA faces challenges, both internally and from competitors, to raise the level of support it provides. In the near future, it will no longer be good enough for an architecture to merely enable the desired behavior (program semantics). Instead, there are a host of other system properties, or "ilities" (e.g., reliability, interoperability, security, quality of service, manageability, extensibility, and scalability) that users will rightly come to expect the OMA to support.

The OMG Object Management Architecture Reference Model (OMA-RM) and the containing OMA Guide, once was (and still ought to be) the central architectural handbook of OMG. The Object and Reference Model Subcommittee (ORMSC) is presently considering updates to these documents. This architectural "green paper"  proposes some areas for discussion that we hope will ultimately lead to improving the OMA-RM and OMA Guide. Our focus is on extending the ORB and services model of OMA to an integrated set of services that enable and enforce ilities.
  



Problem, Objective, Impact

OMG is currently considering the problem of how to update its "Object Management Architecture Reference Model" (OMA-RM). The OMA-RM is a chapter in its OMA Guide, the central architectural handbook of OMG.  The Object and Reference Model Subcommittee (ORMSC), reporting to the OMG Architecture Board, has been formed with that revision as part of its charter.  This document is a position paper for consideration by ORMSC.

The OMA-RM has served OMG well since 1990.  It is both an explanation of the current OMG architecture and a guide to the evolution of that architecture. However, seven years is a long time in the computer field. We assert that it's now time to discuss and revise the OMA-RM to reflect current reality and to facilitate future development. We hope this green paper will provide some useful insights on architectural directions, particularly with respect to componentware, composing components, building scalable systems, and the interactions of components in achieving software ilities. We discuss several specific candidate upgrades to the current OMA-RM and OMA Guide and provide a list of areas where more work is needed to better understand and extend the OMA.


The Object Management Architecture Today

OMA-RM and OMG architecture

The "Object Management Architecture Reference Model" was published in 1990 as part of the OMG Object Management Architecture Guide. In addition to the OMA-RM, the OMA Guide contains additional supporting material, including chapters entitled "Introduction" and "Overview" (describing OMG goals and benefits), "Technical Objectives", and "The Object Model," appendices "Glossary" and "Policies and Procedures."   Revisions of OMA-RM in 1992 and 1995 made small additions, and a more substantial revision was approved in August, 1996, but is not yet part of the currently published OMA Guide.  For the purposes of this paper, we will use the term OMA-RM to refer specifically to the reference model and OMA generally to refer to the entire body of OMG architecture specifications. These include the architectural principles, Common Object Request Broker Architecture, Object Services Architecture, Common Facilities Architecture, Domain Interfaces, and all adopted specifications (even specifications in process).

What the OMA-RM itself explains.

By design, the OMA-RM is a high level architecture. Its function has been "to map out areas to be addressed rather than to impose design constraints." Its modus operandi has been to identify major components without itself defining detailed interface specifications.  The OMG technology adoption process takes care of such specifications. OMA-RM has evolved in several steps:

What the OMA-RM does not explain

The OMA-RM does not explain nor does it preclude a long list of desirable architectural extensions.  Some of these are presaged in the original OMA Guide "Overview" and "Technical Objectives" sections but are not yet realized in the OMA. They are candidates for addition to these sections.  In the next section, we examine several such extensions and discuss the virtue of extending the OMA to cover them.



Possible Extensions to the OMA

We've organized our set of architectural extensions to the OMA into the following subsections, working our way from the most general principles of software architecture to the specifics of interoperating in the real world:


Architectural Principles, Properties, and Frameworks

Architectural Principles

The OMA-RM does not explicitly mention the "architectural principles" that were first described in the Object Services Architecture and now appear in the RFP template. It should refer to these principles explicitly. The architectural principles should probably become a chapter or section in the OMA Guide.

Architectural Properties

The OMA-RM does not currently say much about desirable architectural properties (beyond interoperability).

Software is designed primarily to meet functional specifications---that is, to achieve particular input and output behavior. However, a well-designed system achieves an appropriate balance of other properties: those that encompass its ability to exist in its environment and evolve as that environment changes. Following evolving practice, we call these ilities [Table 1]. Ilities are architectural properties that often can cut across different levels or components of a system's architecture to be properties of the whole. Unlike simple functionality, ilities can include tradeoffs---for example, enhanced interoperability may have been produced at the cost of greater security. Although ilities are sometimes invisible properties of the system as a whole, they represent real (though perhaps unspoken or even unrealized) customer requirements. The enterprise architect or system architect is responsible for ensuring such ilities, and a most appropriate task for an architectural framework is to support them. Currently, the OMA does address security and is beginning to address quality of service, real-time, and composability. It's time for the OMG architecture to address other ilities, such as interoperability through time and space---that is, the ability to evolve to meet new demands. We discuss specific ilities in greater detail below.

Frameworks

There has long been a question as to what the technical distinction is between object services and common facilities, even between platform and domain (e.g., is workflow Platform or Domain Technical Committee?).  Historically, such technical distinctions were mostly ignored and have mainly been treated as convenient intra-organizational divisions of labor.

But the 1996 OMA-RM section on frameworks is three pages long [In contrast, the domain interfaces section is a paragraph just four lines long.], describes an explicit hierarchy of application objects, domain objects, common facilities, and object services, and gives no concrete examples of object frameworks so they remain abstract.  Frameworks appear to be constellations of objects that operate together.  But most object services and common facilities define more than one object class.  So it is not really clear how common facilities and common facility frameworks would differ.  For instance, are OODBs, workflow systems, KBMS systems, repository management systems, and BOFs frameworks or are common facilities? The section on frameworks needs to be re-thought since at present frameworks are really a research area at OMG.
 


 Composability and Componentware

From the beginning, high level goals of OMG have included reusability, interoperability, extensibility, and dynamic evolution.  OMG customers have wanted the ability to assemble applications quickly from standard parts, and OMA framework users were seeking consistent semantics for how shared services work when using the full suite of OMG specifications.  We have made good progress on separable specifications but have said too little about composition of services and facilities.  Current specifications do not provide enough information to realize the desirable the goals of being able to mix-and-match and plug-and-play with alternate implementations of services or facilities.

Composing services with application objects

Current OMG service specifications assume that the application developer understands all the relevant services and invokes them when appropriate. This means that calls to specific service functions (including implementation specific options) become deeply interwoven with the application logic. The interweaving of separate concerns is especially serious in the cases where the service requires insertion of functionality at the calling side of an interaction, as occurs with services such as encryption, authentication, and replication.

To make services appear as componentware within an application, we need better and more structured ways of adding services while minimizing their impact on the application code. Often, service functions can be implicit in application method invocations. Frameworks can protect the application code from being intertwined with calls to service functions. However, it is not clear how to add (chain?) or control implicitly specified services.  Binding times for adding services are not specified nor is there any mechanism to control which users can add services dynamically.

Service Interactions

Before the ORB bus architecture was adopted in 1989-90, some people argued that both versions and DBMS functionality were needed. While it was clear that services needed to interact, no one was satisfied with any particular block diagram or calling tree showing particular services explicitly calling other services.  The CORBA bus architecture, with its uniform set of services hanging from the bus seemed to be a good solution. It allowed separately specified services and deferred the issues of service composition.  OMG has followed this course for the last eight years.  But we still have little experience connecting the services on the bus together to do useful work. [According to the IEEE, an architecture is a collection of functions and interconnections.  Interconnections reveal the relationship between the functional components. Ironically, by mapping calling trees to a set of functions communicating over a single message dispatch bus, OMG has provided only the definition of functions and not the information about interconnections.]

This legacy is visible in OMG discussions about specifying CORBAservices.  Such discussions are marked by a tendency to state that one service might depend on another without explicitly committing to such dependencies.  Another manifestation is seen in the use of IDL. An object's IDL encapsulates its implementation with no mention of service dependencies. (One must examine the implementation to discover them.) On the positive side, this provides implementation independence for clients of interfaces.  On the negative side, it prevents service substitutability and leads to application bloat and large, monolithic ORB's. A side effect is that a high level component like a BOF or an application component may have no way to specify how it uses Object Services (if it does).  OMG users expect higher level OMG objects like facilities to be composed partly from lower level services and they want the ability to spin out stable internal components for independent reuse.

Uses specification or Containment Model needed

Some sort of uses specification is needed to declaratively relate implementations to interfaces on which they depend. Alternatively, some sort of explicit containment graph is needed to relate a higher level component to components it contains or depends on. Hopefully, the CORBA Component RFP will address this.

Binding Times

The OMA-RM does not address how dynamic the binding is for adding new services to existing frameworks (though the old Technical Objectives chapter of the OMA Guide did mention Extensible and dynamic changes like adding new implementations, replacing implementations where the interface has not changed, replacing implementations where the interface is changed, and changing the location of implementations).

Dynamic Dispatch, Interceptors and Extensions

Good news about the OMG bus architecture is that it promises flexibility.  If object A calls object B using the bus architecture, then the call may be transparently local or remote and furthermore the call can be intercepted or filtered by any number of implicit operations which can be executed on the client or the server or somewhere in between to insure that concurrency control is respected if B is a shared object, that B is versioned or not, that A has authorization to access B, that B is coerced to a form that A can accept, that the replicated copies B' and B" receive copies of the request, and so forth. There is a long list of these implicit actions, or extensions. OMA needs a generic mechanism for specifying these implicit service actions without expecting the application programmer to understand and manage all this implicit functionality.

Many Kinds of Extensions, Need for Guards

The interceptors above are just some of a large family of implicit (or explicit) side-effect extension behaviors that set up boundaries that need guards to enforce that the extensional behavior is not bypassed.  Others are:

More Packaging Technology Needed

Principled selection and decomposition into subcomponents can enable substitution and customization by developers other than the original designers.  But there are reasons to hide containment information as well:

Some related issues:


Scalability and the Federation Pattern

Scalability is a desirable property of componentware: we want to build larger systems from components, unrestricted by the particular size or internal organization of the components.

One notion of scalability refers to the ability of a design to maintain a linear relationship between demands on a system and required resources. This is illustrated in the  "Technical Objectives" chapter of the OMA Guide, where scalability is defined as "the effect on request processing times as the numbers of objects accessible to a client increases and the number of requests handled increases."

Build-time componentware definitions might cast scalability as the ability to build larger systems or systems of systems from component parts. An example would be composition as described above in which a common facility might be defined from object services, for example, an OODB as some composition of naming, persistence, query, transactions, security, etc.

An important variant to composition of parts to form a whole is the special case when the parts are similar.  We can define federation to be the composition of like systems that operate together to form a higher level system.  When there was just a single LAN-based CORBA, OMG could choose to not spend to much emphasis on federation interfaces.  But with CORBA interoperability and Visigenics fanned out the the Netscape desktop, the number of machines connected to an ORB might go from 40 to 40 million.  No longer should we assume that there is a single name service, a single transaction service, a single query service, a single trader, ... in such an environment.  Minimally, we'd expect many instances of these services.  And we'd expect them to interoperate with others of their kind, so that name services federate, transactions federate, and so on.  Not only services but also facilities should federate so workflow, OODBs, simulations, etc. would intercommunicate with others of their own kind.

To achieve scalability via federation, OMG must address several architectural issues:

Taken together, with both composition and federation as ways of building complex systems from simpler ones, one can come back to the question of ilities and talk about end-to-end X or top-to-bottom X where X = security, QoS/bandwidth adaptive, real-time guarantees, optimization, maintainability, reliability, affordability, licenseability for reasonable cost, testability, understandability, seamlessness, evolvability, survivability, etc.  When a system, for instance, a communications network is a federation of similar subsystems, then we can talk about end-to-end guarantees.  When a systems is composed of parts, we can talk about top-to-bottom guarantees.


Performance Guarantees and System Management

It is hard to keep your promises if those promises depend on things you can't control. So an application that makes some form of performance or quality of service guarantee needs its underlying infrastructure to expose enough information or controls to enable the keeping of those promises. More globally, if an enterprise system is to know what kind of system-wide performance is being achieved, the system must expose enough information to allow that monitoring.

Real-time and QoS

Engineering is the process of trading among system attributes. Performance, precision, accuracy, and reliability pervade many components of a system.  Real-time and Quality of Service both involve capturing traffic, accuracy, and other meta data from trend data and current data in a system and providing guarantees on certain outcomes, e.g., that a certain class of user might receive some negotiated level of service. Much of the QoS literature focuses on the issues of getting the underlying components (principally the network) to provide QoS guarantees to applications.  Higher-level applications are said to be bandwidth-adaptive or QoS-aware if they can take special advantage of guarantees made by lower levels of the system to perform better and make further guarantees to their own customer applications.

So far CORBA, CORBAservices, or CORBAfacilities are QoS- and bandwidth-insensitive.  This reflects the appropriate emphasis on the semantics of actions, rather than their pragmatic attributes. However, pragmatics also matters; the architecture needs  interfaces for collecting system performance data and for exposing QoS constraints.

OMG is already actively focusing on real-time and QoS via the active Real-time SIG and QoS Working Groups.  A reason to highlight these -ilities in this paper is just to remind us that some kinds of information that must be transmitted between components may be passed in ways other than functional IDL interfaces of the kinds so far specified in OMG.  An implication for portability of service implementations is that the first generation of services and facilities will not be QoS-aware because there are not yet standard ways to transfer this kind of information.  Another implication is that it is likely that OMG compliant first-generation QoS-unaware implementations should remain useful for many QoS-unaware uses (the majority of uses today) even when QoS guarantees are specifiable (that is, QoS-unaware will be a degenerate, special case of QoS-awareness in a similar way to version-unaware is a degenerate case of version-aware where the policy is to keep only the current version and similarly for many other services.)

System Management

We note that one reason many large installations are slow to adopt CORBA-based technology is the lack of system management facilities. System management involves performance measurement, accounting, intrusion detection and security, failure analysis and debugging, and configuration management. These elements have enough in common and are sufficiently fundamental to suggest their treatment in the OMG architecture at more than the "service" level. System management services are critical enablers for componentware because components are black boxes; all debugging must focus on the interaction between components.

Compressibility

Compressibility could have a significant impact on scalability, reliability, affordability, understandability, performance, and QoS in several different ways that affect bandwidth. Compressibility can be achieved by following architectural specifications on the representation and characterization of the data - the idea is that the message attribute could just state that it could be compressed/decompressed by an operator X which would result in a compression ratio Y but it would need CPU resources Z at the sending and V at the receiving end. This could be done independently from the data and application type, other than pointing to X. Then, the decision and the possible compression invocation would be transparently done in the pipe. This raises the issue of whether to overlay the OMA with an attribute driven metadata architecture, which would be useful for other services beyond compression.


Convergence with the Competition

Several current and emerging representational paradigms compete with OMG. Rather than having user communities scatter to a Babel of architectures, OMG must either provide a migration path or subsume the concepts of these alternatives.  OMG may have had the first distributed architecture, but being first is not a guarantee of survival. This suggests extending the  OMA Guide, (either in the chapter on OMA-NG or in the chapter on "Technical Objectives") to provide a road map for convergence with the following:

A Market for Components

Componentware is the industry buzzword for small isolatable chunks of software that can be assembled into large applications.  We discussed above some of the concepts we believe are appropriate to an OMG notion of composition and federation of components. The notion of an economy of componentware is that components are vended separately by potentially many vendors.  OMG has not yet really demonstrated itself to be a componentware community though we have taken great care to adopt an isolation principle for orthogonal object services.  While there are many ORB vendors, there are relatively few object service providers and those mainly vend a collection of components from one vendor. This is, one's ORB vendor is often the source of one's CORBA services.  There is not enough evidence of portable object services or higher level applications that are compositions of collections of services.  Componentware does not per se require a certain variety of object technology.  We note that the ActiveX/COM and more recently the JavaBeans environments have active componentware sub-industries.  OMG has just issued Component Model and Component Scripting RFPs to try to jump-start OMG into contributing to the componentware movement.

Microsoft ActiveX and COM

OMG has already provided guidance in this area. Of course, this is a 600 pound gorilla force to be reckoned with with an active componentware marketplace.

Java

With Java on servers as well as on clients, Java and OMG are increasingly addressing the same market.  It is an open question as to whether the Java and OMG specifications will converge.  Java and IDL are at the same level of representational adequacy, but Java definitions come attached to a programming language.  IDL is language neutral and IDL mappings have been defined for several programming languages. Java benefits from the greater semantic specificity an underlying language provides, but also has an emerging need to directly supply standard Java to X mappings for legacy language applications.  Some of the distance between OMG and Java is narrowing:  JavaSoft is moving toward OMG by adopting into its Enterprise Java both CORBA naming and transactions and making accommodations for OMG IIOP.  OMG is likely to adopt a JavaBean-like component model, Java-based scripting (pure speculation of course!), and harmonization with Objects by Value, Multiple Interfaces, and Portable Object Adapter.  Already, Java libraries are extensive, implemented and conveniently accessible.  Momentum is high.  OMG has a reasonable collection of specifications for middleware services so far unmatched by Java or ActiveX.  And OMG has defined an IDL to Java mapping.  But what happens when the Java class library community implements all the OMG services?  Will the specifications be compliant to OMG services and the defined mappings?  Or will variants spring up?  One example is collection class libraries.  OMG collections are not the same as ODMG collections which are not the same as C++ STL collections. Java collection classes seem more likely to be based on C++ STL. Will there be a time when OMG permits specifications described natively in Java which use Java-to-IDL mappings to insure backwards compatibility to IDL?  Will that become the norm?  Should we just go ahead and use the IDL to Java mapping to convert all OMG specs to Java now to make convergence easier?  Or should we permit OMG specifications written in native Java (when we have IDL to Java and Java to IDL mappings)? Java may soon have its own standards body, similar but not the same as OMG. Java has the potential for producing real working libraries more quickly than the OMG process. If that happens, OMG might find itself less a visionary leader into new directions and more a redundant afterthought.

Web

Information once available only in local file systems is now available via the World Wide Web. The web architecture consists of lightweight clients providing a desktop, servers providing document content, and a means of accessing backend applications that provide semantics often accessible via CGI scripts.   The addition of Java to the client and server side enhances the architecture.  All this has been accomplished without the complexities and simplifications of formal specifications (i.e., IDL.).  The recent addition by Netscape of Visigenic's ORB provides one reasonable way to glue the web and ORB architectures together.  Interestingly, it is possible to imagine adding services to a URL Request Broker without ever introducing IDL, CORBA, or OMA.  For instance, one can add an annotation service on a client to access a URL and any URL annotation repositories and return annotated documents.  This is very like the OMG interceptor architecture but with proxy based intermediary services interposed between client and server.  There are many similar services (e.g., add advertisements, strip advertisements, micropayment, microlicense, PICS, etc.).  The puzzle for OMG is how to converge the web and CORBA architectures so there will not become two parallel sets of services (e.g., web traders and CORBA traders, web versions and CORBA versions).  A scenario for convergence might be if there is a web document guarded by the OMG security service, subject to the annotation service, that can use OMG versioning (if we had it). A fitting name for the addition of Internet/Web motivated services might be Internet Services Architecture, an extension to the OMA.

Database Management Systems

While the original "Introduction" to the OMA Guide listed Object Database Interfaces in scope for OMG and OMG has defined services for persistence, transactions, queries, naming, and collections, there is no OMG compositional facility for an OODB or Object-relational DBMS, nor are there gateway interfaces for SQL3, ODMG, or ODBC/JDBC interface defined by OMG except via a string API call to the Query Service (so for instance, there is no defined mapping from IDL to relations or vice versa).  Since a lot of the world's data is in relational DBMS systems (and a little is in OODBs) there is a need for OMG interfaces to these kinds of DBMS systems.  Furthermore, there is an opportunity for OMG to define federation interfaces that access multiple data sources in the network uniformly, as is done in various experimental communities (e.g., OMG Internet SIG's OTAM, DARPA I*3 and Data Server, MCC Infosleuth).

Knowledgebase Management Systems

Loosely, if a KBMS is a composite of objects, rules, constraints, before-and-after methods, etc., then one would like to find a path to grow OMG's object modeling capability to add these extra representational capabilities.

Mobile Code

For most of its lifetime, OMG has provided only a partial solution to distribution, namely object reference at a distance.  Only recently has it added Call by Value for moving object state and Mobile Agents for adding mobile code.  Java-based schemes are rapidly evolving and OMG's schemes are following Java.

Agent Management Architecture

OMG has issued and is considering responses to the Mobile Agents RFP.  This direction could add mobile state, mobile code, and mobile objects to the OMG OMA.  An architectural puzzle for OMG is whether agents subsume objects the way that objects subsume abstract data types. [Object systems might someday come to be viewed as degenerate agent systems, ones where the agents are passive and immobile.  When that day comes, we'll need to change the OMG and OMA to the AMG and AMA. ]  Even if agents are just an "optional" extension to the OMA and not a core topic, the diverse family of technologies, ideas and directions of agent technology could lead to a collection of RFPs to cover autonomous action, cooperation and negotiation, acting on behalf of others, proactive and reactive control structures, intelligence in reacting to its environments and planning, scheduling, and/or learning.

RM-ODP

The Open Distributed Processing community has developed a number of concepts that complement OMG's architecture:

Patterns

There is now substantial and useful literature on OO patterns, which are abstract specifications of the behavior of constellations of objects.  Pattern collections can be mined for new OMG services.  The patterns methodology can be incorporated into the OMG technology base.  Puzzles involve rationalizing vocabularies for patterns and frameworks.


Other Extensions

The following extensions are already being discussed in OMG and we are not adding much to this discussion except to list them as significant candidate extensions to the OMA-RM.

Views of the Architecture

We need some additional views of the OMA architecture, not just the software bus view. Other views might explain how services are interconnected, how ilities are inserted, how visibility and packaging is supported, dataflow, physical distribution, etc. This is in addition or complementary to possibly adopting ODP viewpoints.

Semantics

There is already activity in OMG to address the need to say more about specifications than just their interface and an English explanation of their intended semantics.

Object Model Extensions

This paper doesn't currently address object model extensions needed except to mention some ideas:

Domain Interface Architecture

The OMG-RM provides short descriptions of Object Services, Common Facilities, and Domain Interfaces.  Separate substantial Object Services Architecture and Common Facilities Architecture documents currently exist.  Historically, these have proved reasonably valuable to the Platform technical committee in setting the scope and road maps for the Object Services Task Force and Common Facilities Task Force.  (On the other hand, there never was a predecessor ORB Architecture document apart from the growing CORBA specification.)  The Domain Technical Committee has chartered a broad collection of task forces and SIGs but there is currently no Domain Interfaces Architecture (DIA) to guide OMG in how to populate the DTC space. This has led to recent (fairly emotional) discussions on the need for such a document.  Problems have arisen between DTC groups on boundaries between, say, common business objects and manufacturing objects partly because there are no criteria for setting boundaries except one group "getting there first."  On the other hand, having architecture documents has not guaranteed Despite these problems, such architecture documents do substantially help OMG move forward by providing "stakes in the ground."  The need for a DIA document could be a discussion point in ORMSC (or DTC) that could lead to a new work item. If so, someone would have to come forward with at least the sketch of a strawman document.  [It appears that the Common Business Object Working Group of the Business Object Domain Task Force is preparing an RFI to develop a DIA.]  A DIA document might mention the areas that OMG currently is committed to: and other potential areas like and provide guidance on domain scope.  The potential space is very large.  Other domain standards populate parts of that space (e.g., STEP).

Needed Services and Common Facilities


Conclusion and Recommendations

OMG still offers the most comprehensive collection of specifications for distributed middleware and is an active community with strong industry backing.  It must continue to evolve rapidly to survive since it does not stand alone -- there are rival technologies like ODP (more conceptual), agents (richer abstraction base), Java (broadly based implementations in rapid fire evolution), and DCOM (strong market penetration).  OMG must develop convergence stories for each of these  to best represent the needs of its communities.

The OMA-RM has historically been and continues to be useful "as is."  The most conservative position is to change it as little as possible since it has served as a permissive guide to allow many architectural extensions to be layered on top as the entire body of OMA is populated.  The original OMA-RM reflected a vision of the future.  Now some of that future is in place. Its role may need to grow to explain that architecture. And its vision of the future may need to be revised to reflect the better perspective of six years of experience.  As a starting point for those discussions, we recommend:


Copyright 1997 Object Services and Consulting, Inc. Permission is granted to copy this document provided this copyright statement is retained in all copies.

Copyright 1997 Microelectronics and Computer Technology Corporation.   Permission is granted to copy this document provided this copyright statement is retained in all copies.

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.

This research is sponsored by the Object Infrastructure Project of the Microelectronics and Computer Technology Corporation.  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 Microelectronics and Computer Technology Corporation or its member companies.

Acknowledgments:   This paper is based on lessons learned primarily in the OBJS project Scaling OSAs to the Internet and the MCC project Object Infrastructure Project. The authors gratefully acknowledge inputs received from Art Goldschmidt on lessons learned in the National Industrial Information Infrastructure Consortium (NIIIP) and from Gabor Seymour (Motorola).