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I have gone through different questions/articles on Message Brokers and ESBs(Even on stackoverflow). Still not a clue as what is the CLEAR demarcating difference between an Message Broker and an ESB? Now here I am trying to compare products, Websphere Broker and Mule ESB!!

Firstly , is (any version) Webshere Broker an ESB? Our IBM product guys claims it to be an ESB!(I am not surprised about that).

My limited information tells me that a Message Broker works on a HUB-SPOKE model. However the ESB works on a bus architecture. Now what on earth is that supposed to mean? I have read than if the HUB fails(unavailable I guess) then the broker completely fails. Which is not the case of an ESB(So those guys say). What I dont understand here is What if the BUS fails?

Now the usual stuff about an ESBs and Brokers is that , they provide routing,transformation, orchestration etc.. So if both of them provide this, then why would I choose one over the other.

Another area of conflict is regarding the TRANSFORMATION. Does ESBs facilitate it in a different way when compared to Message Brokers? I would really love some insight on this.

Now talking about HORIZONTAL scaling. Who outperforms the whom? Or are both of them equally scalable in terms of complexity(or any other factors). Ofcourse cost wise, Webshpere Broker is gonna charge you for each box(let alone each cpu). I believe , even the commercial MULE ESB doesnt do that. Leaving aside the Cost part of it, what are the implications of ESB scaling and Message Broker scaling. I happen to know you can scale up to Service Level in ESB. Is this possible in a Message Broker?

You can use a transformation broker without a service bus, and vice versa. In terms of specific products I dont think any one is purely one or the other because of the way each complements the other. Some products are stronger in the one area, other stronger in another. Perhaps a choice needs to be made based on which function best covers an individual problem.

A broker may have better built-in lego blocks for constructing a transformation chain than an ESB product does. A broker pressed into service as an ESB may be crushed under load and not scale well, or may lack robust journaling and tools for dealing with journals.

Some ESBs allow database updates to be rolled back and queues to be replayed into a corrected application once an egregious error in logic has been uncovered and fixed. I dont think most brokers integrate that level of transactional support. For this to work at all your transactions almost have to be business events (a sale, a renewal, a change of ownership, etc.) rather than something like RPCish database updates.

I just wrote a blog post describing the integration elements often attributed to service buses, covering the transformation sides of it as /2011/04/08/integration-how-and-where

Disclaimer: I am an IBM consultant and specialise in WebSphere ESB. This comment isnt left in any official capacity.

An ESB is more of an architectural pattern or concept than a product – broadly, a service-based way of engineering loose coupling. Its definition is fought over and not exactly set in stone. In general, an ESB is set of unrelated (in a technical sense) services – they expose interfaces, and they consume them from other services. Generally there isnt a hub and spoke architecture involved, although there can be.

IBM certainly markets both WebSphere Message Broker and WebSphere ESB as products that make it easy to build an ESB (along with the DataPower hardware appliance). They have different technological roots, but have some overlap in purpose. Also, thats not to say you cant build an ESB with lots of other things that arent branded as an ESB product.

That doesnt answer all your questions, but hopefully addresses the IBM part.

Thanks Andrew.I am happy to know you are a specialist on WebSphere ESB.I have one thing clear.ESB is not a product and is a fundamental architectural view:A BUS.Now, if ESB has been in place only since 2002 onwards,why was it even coined? I believe there is a lot of debate as to who Invented ESB.If the Websphere Broker can be made do all the stuff an ESB does, then why claim it to be an ESB product?I even have seen a Red Book which shows you How to Implement an ESB with Websphere Broker.

I really dont know if this is a good analogy. Our house maid cooks for me. My mother would also cook for me. However I cannot call my mother a housemaid athough she does the duties of a housmaid, could I(If I did so, thats the end of dinner)? There is a fundamental difference which cannot be overcome?

Gartners most senior middleware analyst, Roy Schulte asserted that: The most direct ancestor to the ESB was Candles Roma product from 1998, later called Candle Pathwai. Candle was acquired by IBM in April 2004 – an irony that will not be lost on either Tibco or Sonic Software, since IBM has only recently begun to claim that it too has an ESB of its own – IBMs Steve Mills told ComputerWire that: I know we do [have an ESB],in fact Ive been delivering ESB functionality for many years.

Read the who thing here ESB Inventor RIDDLE /blog/archives/2005/08/

The difference between a Message Broker and an ESB is mainly the word bus.

To me, a Message Broker is one (usally big) process that transforms data from one structure to another structure or modifies content.

An ESB is a message oriented middleware (MOM) plus additional services, one of whichcould bea Message Broker. So an ESB can include a Message Broker as one of its components. A Bus consists of more than one processes, otherwise I wouldnt call it a bus. The nature of a bus is that there are multiple components serving different tasks, each one communicating over a MOM and adhering to some form of common data format. A bus would consist of: applications sending data to the MOM, database adapters, Message Brokers, MOM bridges, etc.

The separation is a bit gradual, but the biggest difference between a Message Broker architecture and a Bus is that ofgranularity. If your task is to integrate applications A, B, .., Z and a couple of databases, you can do this with one big Message Broker connecting each and everyone. Or with an ESB where multiple small components take over just little tasks. For example one adapter connects to A, another one to B (but they dont do transformation), then each one sends their stuff to one (or more) Message Broker, each of which should be kept as simple as possible – e.g. not having to know about the data model of A or B. A good ESB should have a common data definition on the bus, abstracting from the differentness of individual applications.

TRANSFORMATION: an ESB doesnt help with transformation, unless it comes with a Message Broker. But each good ESB should include a Message Broker anyway. The Message Broker should be your buss expert for transformations, but nothing else.

HORIZONTAL scaling: if you only have 3 things to connect (now and forever), its probably not worth the effort to get a full-blown ESB. A Message Broker has the advantage of being just one big process. You can configure everything in there and have a central location for all your data mappings, filtering and routing.

But if you have 30 applications to connect, one Message Broker would probably come to grinding halt. Of course you can buy more instances, run things redundant, etc. but you should change your strategy to localize jobs. Each applications adapter (could be one little Message Broker instance each) should be able to generate and/or receive an abstracted common data model (e.g XML with a shared XSD). There could also be a central Message Broker for transformation tasks, but that instance should be unaware of data model A or B. So an ESB should move the processing to the expert component instead of keeping everything in a central place.

I just read this article by Udi Dahan a few days ago, which might give you a more clear view of what I feel is one fundamental difference.

The rule that there can only be a single publisher for a given event type is one of the things that differentiates buses from brokers, though both obviously allow you to have multiple subscribers

Unfortunately, there are many broker-style technologies out there that are being marketed under the banner of the Enterprise Service Bus. While some products have the ability to be deployed in both a centralized and distributed fashion (sometimes called federated or embedded mode), many do not enforce the single publishing endpoint per event-type rule.

Without this constraint, it is just too easy to make mistakes.

An Enterprise Service Bus provides three key values to the Business :

Context- or content- based routing of transactions;

Transformation from one message domain or transport to another message domain or transport;

ESBs provide loose coupling of services, allow services to be reconstituted into entirely different application contexts than when the services were first envisioned or developed, and promote reuse of applications without the need to recode applications. WebSphere Message Broker (or now is called IBM Integration Bus) is a prime example of an Enterprise Service Bus. For an example of simplicity of code that brings to bear great power in a few lines, you can view my post here : The fundamental construct inside the IIB runtime is called theLogical Message Tree(LMT). Everything that the developer wants to do is some type of operation on the LMT. ESQL is the most efficient language a developer can use to perform these operations on the LMT, although many other languages are supported (for example, Java, PHP, Python, etc.) No other product comes close to the efficiency and ease of developing ESB applications than IBM Integration Bus since 90 percent of the coding of these applications is done by dragging and dropping nodes onto a pallet. That leaves only 10 percent of the coding to be done by the Message Flow developer. By the way, WebSphere ESB has been discontinued by IBM and many of the competing products to IBM Integration Bus have not seen any new development on them for several years now. A list of various ESB product offerings can be seen at .

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