|By Mark Little, Jim Webber||
|April 22, 2003 12:00 AM EDT||
In July 2002, BEA, IBM, and Microsoft released a trio of specifications designed to support business transactions over Web services. These specifications - BPEL4WS, WS-Transaction, and WS-Coordination - together form the bedrock for reliably choreographing Web services-based applications, providing business process management, transactional integrity, and generic coordination facilities respectively.
This article introduces the underlying concepts of Web Services Coordination, and shows how a generic coordination framework can be used to provide the foundations for higher-level business processes. In future articles, we will demonstrate how coordination allows us to move up the Web services stack to encompass WS-Transaction and on to BPEL4WS.
In general terms, coordination is the act of one entity (known as the coordinator) disseminating information to a number of participants for some domain-specific reason. This reason could be in order to reach consensus on a decision like a distributed transaction protocol, or simply to guarantee that all participants obtain a specific message, as occurs in a reliable multicast environment. When parties are being coordinated, information known as the coordination context is propagated to tie together operations that are logically part of the same coordinated work or activity. This context information may flow with normal application messages, or may be an explicit part of a message exchange and is specific to the type of coordination being performed. For example, a security coordination service will propagate differently formed contexts than a transaction coordinator.
Despite the fact that there are many types of distributed applications that require coordination, it will be no surprise to learn that each domain typically uses a different coordination protocol. In transactions, for example, OASIS Business Transactions Protocol and Object Management Group's Object Transaction Service are solutions to specific problem domains that are not applicable to others since they are based on different architectural styles.
Given the domain-specific nature of these protocols (i.e., loosely coupled transactional Web services and tightly coupled transactional CORBA objects) there is no way to provide a universal solution without jeopardizing efficiency and scalability in each individual domain; and not everyone wants to (or can afford to) have a full-blown transaction processing system in order to do coordination. However, both of these protocols have the underlying requirement for propagating contextual information to participants, and therefore it would make some sense if that mechanism could be made generic, and thus reused. On closer examination, we find that even solely within the Web services domain we encounter situations where coordination is a requirement of several different types of problem domain, such as workflow management and transaction processing, but where the overall models are very different yet that same requirement for coordination is still present.
The fundamental idea underpinning WS-Coordination is that there is indeed a generic need for propagating context information in a Web services environment, which is a shared requirement irrespective of the applications being executed. The WS-Coordination specification defines a framework that allows different coordination protocols to be plugged in to coordinate work between clients, services, and participants (see Figure 1). The WS-Coordination specification talks in terms of activities, which are distributed units of work involving one or more parties (which may be services, components, or even objects). At this level, an activity is minimally specified and is simply created, made to run, and then completed.
In Figure 1, we suggest that the framework is useful for propagating security, workflow, or replication contexts, though this is by no means an exhaustive list. Nonetheless, whatever coordination protocol is used, and in whatever domain it is deployed, the same generic requirements are present:
The first three points are directly the concern of WS-Coordination, while the fourth is the responsibility of a third-party entity, usually the client application that controls the application as a whole. These four roles and their interrelationships are shown in Figure 2.
The WS-Coordination framework exposes an Activation Service that supports the creation of coordinators for specific protocols and their associated contexts. The process of invoking an activation service is done asynchronously, so the specification defines both the interface of the activation service itself, and that of the invoking service, so that the activation service can call back to deliver the results of the activation - namely a context that identifies the protocol type and coordinator location. These interfaces are presented in Listing 1, where the activation service has a one-way operation that expects to receive a CreateCoordinationContext message, and correspondingly the service that sent the CreateCoordinationContext message expects to be called back with a CreateCoordination ContextResponse message, or informed of a problem via an Error message.
Once a coordinator has been instantiated and a corresponding context created by the activation service, a Registration Service is created and exposed. This service allows participants to register to receive protocol messages associated with a particular coordinator. Like the activation service, the registration service assumes asynchronous communication and so specifies WSDL for both registration service and registration requester (see Listing 2).
When a participant is registered with a coordinator through the registration service, it receives messages that the coordinator sends (for example, "prepare to complete" and "complete" messages if a two-phase protocol is used); where the coordinator's protocol supports it, participants can also send messages back to the coordinator.
The role of terminator is generally played by the client application, which at an appropriate point will ask the coordinator to perform its particular coordination function with any registered participants - to drive the protocol through to its completion. On completion, the client application may be informed of an outcome for the activity, which may vary from simple succeeded/ failed notification through to complex structured data detailing the activity's status.
The context is critical to coordination since it contains the information necessary for services to participate in the protocol. It provides the glue to bind all of the application's constituent Web services together into a single coordinated application whole. Since WS-Coordination is a generic coordination framework, contexts have to be tailored to meet the needs of specific coordination protocols that are plugged into the framework. The format of a WS-Coordination context is specifically designed to be third-party extensible and its contents are as follows:
While the first three points are common sense, the fourth is somewhat more interesting. Since WS-Coordination is generic, it is of very little use to applications without augmentation, and this is reflected in the part of the WS-Coordination XML schema for contexts. In Listing 3, the schema states that a context consists of a URI that uniquely identifies the type of coordination that is required (xs:anyURI), an endpoint where participants to be coordinated can be registered (wsu:PortReferenceType), and an extensibility element designed to carry specific coordination protocol context payload (xs:any), which can carry arbitrary XML payload. (Note: This type also inherits some useful features from its parent in the form of a time-to-live value and an identifier.)
Coordinating Business Processes on the Web
To show WS-Coordination in action, we'll consider a centralized sign-on service that enables a client application to authenticate once, and then use given credentials to access a number of Web services, and to de-authenticate from the system with a single operation irrespective of the number of Web services that are invoked. (Note: It's important to note that although the coordination strategy outlined here is reasonable enough, the patter as a whole isn't industrial strength since we avoid clouding the coordination issues by drawing on other useful technologies such as XML encryption and XML signature, which a truly trustworthy implementation would utilize. You should remember while following this example through that a real implementation would draw heavily on security standards like XML-encryption to provide the necessary privacy and XML digital signatures to provide authenticity.) The initial coordination pattern for this scenario is captured in Figure 3.
Here we see the initial stages of the application. The client application locates an activation service and sends it a message asking for the creation of a security coordinator and a corresponding security context, passing appropriate user credentials as part of the activation process as shown in Listing 4.
Assuming that a security coordination service has been registered with the coordination framework, a coordinator is created (and exposed as a registration service) and a context like that in Listing 4 is duly returned to the client application as part of the CreateCoordinationContextResponse message.
The client application interacts with its component Web services sending and receiving messages as normal, with the exception that it embeds the coordination context (which carries the security information) in a SOAP header block in its messages to provide authenticity credentials for those services that are invoked.
Let's assume that a service understands the protocol messages associated with our simple centralized sign-on service, and furthermore hasn't registered a participant previously. Once the service receives a SOAP message containing a security context header (see Listing 5), it registers a participant with the coordinator using the details provided in the context (via the WS-Coordination registration service URI, for example). This registration operation occurs every time a service receives a particular context for the first time, which ensures that all services register participants within the activity.
When the client decides to terminate its session and log out of the services it has been using, it sends a completion message to the coordinator; in turn, the coordinator informs each registered participant to revoke the privileges for the client application, preventing it from using their corresponding services. Any subsequent calls by the client to that service with the same context will result in the service being unable to register a participant since the context details will no longer resolve to a live coordinator to register with (see Figure 4).
At some point, the client application finishes its work and must run the completion protocol to force its own system-wide logoff. To do this, it sends a security protocol logoff message to the security coordinator. This message is entirely out-of-scope of WS-Coordination and is instead defined by the specification of our security protocol which plugs in to the WS-Coordination framework. The completion message is shown in Listing 6.
In response to receiving this message, the security coordinator informs each of its registered participants to terminate the user's current session. To do this, it sends each of the participants a signOut message to which they respond with a signedOut message, confirming that the user is no longer authenticated with that particular participant's associated service. The pertinent parts of the signOut and signedOut messages are shown in Listing 7.
Once a signedOut message has been received from each of the enrolled participants, it can report back to the client application that its session has been ended. The final message in our WS-Coordination protocol is the loggedOut response message from the security coordination to the client (see Listing 8).
Advanced Usage Scenarios
In our security coordination example, the overall architecture is relatively static and known in advance of the coordination. However, it may be that in a business-to-business scenario we would like the ability to coordinate arbitrary groups of Web services as part of a single, logical, coordinated application. WS-Coordination supports this through a scheme known as interposition.
Interposition is a way of creating a hierarchy of coordinators, each of which looks like a simple participant to coordinators higher up the coordination tree, yet acts just like a normal coordinator for participants lower down the tree. Coordinators become registered within this hierarchy if the client application sends a CreateCoordination Context message to an activation service along with a valid context. When the receiving activation service creates the new context (and associated coordinator/registration service), it uses the original context to determine the endpoint of its superior coordinator (a.k.a. registration service) and enrolls the new coordinator with it.
In Figure 5 we see a typical interposed coordinator arrangement spanning three different enterprises using two different coordination protocols. This arrangement is arrived at through a client application creating a top-level context and then invoking Web services within the bounds of its partner enterprises. In the noninterposed case, upon first receipt of a context embedded in a SOAP header a service registers a participant with the coordinator identified by the context. However, in this situation, for reasons such as security or trustworthiness, the service enrolls its own coordinator by sending an activation message loaded with the top-level context to a local activation service, and then registers with the newly created local coordinator. (Note: By using ts own coordinator, the service or domain in which it resides only exposes the coordinator to the superior and not the individual participants. This may be useful in restricting the amount of information that can flow out of the domain and hence be available to potentially upotentially unsecure or untrusted individuals/services.)
Having received a context with an activation message, the newly created coordinator duly registers itself with the registration service that the context advertises. The top-level coordinator is unaware of this arrangement since it sees the interposed coordinator as a participant, while the local participants are coordinated by their own local coordinator, which confers the following advantages:
In Figure 5 Enterprise A uses the same coordination protocol as the top-level coordinator. In this case, Enterprise A's coordinator coordinates local participants according to the same protocol as the top-level. However, since only the outcome of the local coordination needs to be sent over the Internet to the top-level coordinator, and not the more abundant coordination protocol messages, this approach is performance-optimized, compared to registering Enterprise A's participants directly with the top-level coordinator.
For Enterprise B and Enterprise C, the same performance benefit exists, although the real focus of coordinating these participants is the fact that they are coordinated with different protocols that suit the particular enterprise's needs and not necessarily the same coordination protocol used at the top level. Since the local coordinator for each enterprise is effectively "bilingual" in the coordination protocols they understand (knowing both the participant aspects of the top-level coordination protocol and the coordinator aspects of their own internal coordination protocols), different coordination domains can easily be bridged without adding complexity to the overall architecture.
WS-Coordination looks set to become the adopted standard for activity coordination on the Web. Out of the box, WS-Coordination provides only activity and registration services, and is extended through protocol plug-ins that provide domain-specific coordination facilities. In addition to its generic nature, the WS-Coordination model also scales efficiently via interposed coordination, which allows arbitrary collections of Web services to coordinate their operation in a straightforward and scalable manner.
Though WS-Coordination is generically useful, at the time of this writing only one protocol that leverages WS-Coordination has been made public: WS-Transaction We'll look at this protocol in our next article.
|Sei ES 06/09/03 09:28:00 PM EDT|
We tend to equate Java = Sun. Today, my believe is not so. IBM & others are very deep into Java as well. Moreover, WS is not about Java. WS is independent of tools.
|Mark Little 05/07/03 04:54:00 AM EDT|
I think Microsoft might have a few things to say about "Java is the thread ..." since their offerings won't be Java based ;-) I don't have any insights I can share as to what Sun is doing in this area, but there's obviously a lot going on in the Java space, what with J2EE and JCP, and there has been a lot of effort over the last year on Web Services in J2EE. So, maybe it's just a matter of timing?
|Donald Hsu 05/06/03 06:13:00 AM EDT|
It seems great that BEA, Microsoft and IBM are all making millions $$$ on WS-coordination effort to make their platform, software compatible. But what about Sun? What kind of role it plays? After all, Java is the thread for all of these efforts. Sun should play more active role in Web Server and Web Services market by jumping onto the bandwaggon!
DevOps Summit 2015 New York, co-located with the 16th International Cloud Expo - to be held June 9-11, 2015, at the Javits Center in New York City, NY - announces that it is now accepting Keynote Proposals. The widespread success of cloud computing is driving the DevOps revolution in enterprise IT. Now as never before, development teams must communicate and collaborate in a dynamic, 24/7/365 environment. There is no time to wait for long development cycles that produce software that is obsolete at launch. DevOps may be disruptive, but it is essential.
Dec. 18, 2014 09:45 PM EST Reads: 883
“In the past year we've seen a lot of stabilization of WebRTC. You can now use it in production with a far greater degree of certainty. A lot of the real developments in the past year have been in things like the data channel, which will enable a whole new type of application," explained Peter Dunkley, Technical Director at Acision, in this SYS-CON.tv interview at @ThingsExpo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
Dec. 18, 2014 11:30 AM EST Reads: 925
SYS-CON Events announced today that Windstream, a leading provider of advanced network and cloud communications, has been named “Silver Sponsor” of SYS-CON's 16th International Cloud Expo®, which will take place on June 9–11, 2015, at the Javits Center in New York, NY. Windstream (Nasdaq: WIN), a FORTUNE 500 and S&P 500 company, is a leading provider of advanced network communications, including cloud computing and managed services, to businesses nationwide. The company also offers broadband, phone and digital TV services to consumers primarily in rural areas.
Dec. 18, 2014 11:00 AM EST Reads: 2,121
The major cloud platforms defy a simple, side-by-side analysis. Each of the major IaaS public-cloud platforms offers their own unique strengths and functionality. Options for on-site private cloud are diverse as well, and must be designed and deployed while taking existing legacy architecture and infrastructure into account. Then the reality is that most enterprises are embarking on a hybrid cloud strategy and programs. In this Power Panel at 15th Cloud Expo (http://www.CloudComputingExpo.com), moderated by Ashar Baig, Research Director, Cloud, at Gigaom Research, Nate Gordon, Director of T...
Dec. 18, 2014 10:30 AM EST Reads: 2,252
The Internet of Things is not new. Historically, smart businesses have used its basic concept of leveraging data to drive better decision making and have capitalized on those insights to realize additional revenue opportunities. So, what has changed to make the Internet of Things one of the hottest topics in tech? In his session at @ThingsExpo, Chris Gray, Director, Embedded and Internet of Things, discussed the underlying factors that are driving the economics of intelligent systems. Discover how hardware commoditization, the ubiquitous nature of connectivity, and the emergence of Big Data a...
Dec. 18, 2014 10:15 AM EST Reads: 2,076
"BSQUARE is in the business of selling software solutions for smart connected devices. It's obvious that IoT has moved from being a technology to being a fundamental part of business, and in the last 18 months people have said let's figure out how to do it and let's put some focus on it, " explained Dave Wagstaff, VP & Chief Architect, at BSQUARE Corporation, in this SYS-CON.tv interview at @ThingsExpo, held Nov 4-6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
Dec. 18, 2014 10:00 AM EST Reads: 1,782
ARMONK, N.Y., Nov. 20, 2014 /PRNewswire/ -- IBM (NYSE: IBM) today announced that it is bringing a greater level of control, security and flexibility to cloud-based application development and delivery with a single-tenant version of Bluemix, IBM's platform-as-a-service. The new platform enables developers to build ap...
Dec. 18, 2014 10:00 AM EST Reads: 1,895
SYS-CON Events announced today that IDenticard will exhibit at SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. IDenticard™ is the security division of Brady Corp (NYSE: BRC), a $1.5 billion manufacturer of identification products. We have small-company values with the strength and stability of a major corporation. IDenticard offers local sales, support and service to our customers across the United States and Canada. Our partner network encompasses some 300 of the world's leading systems integrators and security s...
Dec. 18, 2014 09:30 AM EST Reads: 1,886
"People are a lot more knowledgeable about APIs now. There are two types of people who work with APIs - IT people who want to use APIs for something internal and the product managers who want to do something outside APIs for people to connect to them," explained Roberto Medrano, Executive Vice President at SOA Software, in this SYS-CON.tv interview at Cloud Expo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
Dec. 18, 2014 09:00 AM EST Reads: 1,223
Nigeria has the largest economy in Africa, at more than US$500 billion, and ranks 23rd in the world. A recent re-evaluation of Nigeria's true economic size doubled the previous estimate, and brought it well ahead of South Africa, which is a member (unlike Nigeria) of the G20 club for political as well as economic reasons. Nigeria's economy can be said to be quite diverse from one point of view, but heavily dependent on oil and gas at the same time. Oil and natural gas account for about 15% of Nigera's overall economy, but traditionally represent more than 90% of the country's exports and as...
Dec. 18, 2014 06:00 AM EST Reads: 739
The Internet of Things is a misnomer. That implies that everything is on the Internet, and that simply should not be - especially for things that are blurring the line between medical devices that stimulate like a pacemaker and quantified self-sensors like a pedometer or pulse tracker. The mesh of things that we manage must be segmented into zones of trust for sensing data, transmitting data, receiving command and control administrative changes, and peer-to-peer mesh messaging. In his session at @ThingsExpo, Ryan Bagnulo, Solution Architect / Software Engineer at SOA Software, focused on desi...
Dec. 17, 2014 11:15 PM EST Reads: 1,275
"At our booth we are showing how to provide trust in the Internet of Things. Trust is where everything starts to become secure and trustworthy. Now with the scaling of the Internet of Things it becomes an interesting question – I've heard numbers from 200 billion devices next year up to a trillion in the next 10 to 15 years," explained Johannes Lintzen, Vice President of Sales at Utimaco, in this SYS-CON.tv interview at @ThingsExpo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
Dec. 17, 2014 11:00 PM EST Reads: 1,347
"For over 25 years we have been working with a lot of enterprise customers and we have seen how companies create applications. And now that we have moved to cloud computing, mobile, social and the Internet of Things, we see that the market needs a new way of creating applications," stated Jesse Shiah, CEO, President and Co-Founder of AgilePoint Inc., in this SYS-CON.tv interview at 15th Cloud Expo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
Dec. 17, 2014 08:00 PM EST Reads: 1,316
SYS-CON Events announced today that Gridstore™, the leader in hyper-converged infrastructure purpose-built to optimize Microsoft workloads, will exhibit at SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. Gridstore™ is the leader in hyper-converged infrastructure purpose-built for Microsoft workloads and designed to accelerate applications in virtualized environments. Gridstore’s hyper-converged infrastructure is the industry’s first all flash version of HyperConverged Appliances that include both compute and storag...
Dec. 17, 2014 06:30 PM EST Reads: 1,226
Today’s enterprise is being driven by disruptive competitive and human capital requirements to provide enterprise application access through not only desktops, but also mobile devices. To retrofit existing programs across all these devices using traditional programming methods is very costly and time consuming – often prohibitively so. In his session at @ThingsExpo, Jesse Shiah, CEO, President, and Co-Founder of AgilePoint Inc., discussed how you can create applications that run on all mobile devices as well as laptops and desktops using a visual drag-and-drop application – and eForms-buildi...
Dec. 17, 2014 11:45 AM EST Reads: 1,448
We certainly live in interesting technological times. And no more interesting than the current competing IoT standards for connectivity. Various standards bodies, approaches, and ecosystems are vying for mindshare and positioning for a competitive edge. It is clear that when the dust settles, we will have new protocols, evolved protocols, that will change the way we interact with devices and infrastructure. We will also have evolved web protocols, like HTTP/2, that will be changing the very core of our infrastructures. At the same time, we have old approaches made new again like micro-services...
Dec. 16, 2014 11:45 PM EST Reads: 1,287
Code Halos - aka "digital fingerprints" - are the key organizing principle to understand a) how dumb things become smart and b) how to monetize this dynamic. In his session at @ThingsExpo, Robert Brown, AVP, Center for the Future of Work at Cognizant Technology Solutions, outlined research, analysis and recommendations from his recently published book on this phenomena on the way leading edge organizations like GE and Disney are unlocking the Internet of Things opportunity and what steps your organization should be taking to position itself for the next platform of digital competition.
Dec. 15, 2014 11:45 PM EST Reads: 1,653
The 3rd International Internet of @ThingsExpo, co-located with the 16th International Cloud Expo - to be held June 9-11, 2015, at the Javits Center in New York City, NY - announces that its Call for Papers is now open. The Internet of Things (IoT) is the biggest idea since the creation of the Worldwide Web more than 20 years ago.
Dec. 15, 2014 10:30 AM EST Reads: 6,867
As the Internet of Things unfolds, mobile and wearable devices are blurring the line between physical and digital, integrating ever more closely with our interests, our routines, our daily lives. Contextual computing and smart, sensor-equipped spaces bring the potential to walk through a world that recognizes us and responds accordingly. We become continuous transmitters and receivers of data. In his session at @ThingsExpo, Andrew Bolwell, Director of Innovation for HP's Printing and Personal Systems Group, discussed how key attributes of mobile technology – touch input, sensors, social, and ...
Dec. 15, 2014 10:00 AM EST Reads: 1,949
In their session at @ThingsExpo, Shyam Varan Nath, Principal Architect at GE, and Ibrahim Gokcen, who leads GE's advanced IoT analytics, focused on the Internet of Things / Industrial Internet and how to make it operational for business end-users. Learn about the challenges posed by machine and sensor data and how to marry it with enterprise data. They also discussed the tips and tricks to provide the Industrial Internet as an end-user consumable service using Big Data Analytics and Industrial Cloud.
Dec. 15, 2014 10:00 AM EST Reads: 1,624