Yep, my own. Although it may have some shared ideas, this is not a group agreement, nor the savior of what is now known as SOA (which is what is being done so far), nor something made for others to follow. It is just what I believe, what I follow, and what I teach each time I can.

So, here it is.

SOA MANIFESTO

1. Commons.
a. SOA is an acronym composed of the words Service Oriented Architecture, which relates to an architectural style that is based on the rules of the service metaphor.
b. A Metaphor is an application of the figure of speech concept to the IT design discipline. Using metaphors in architectural design actually refers to observing the rules of behavior of a particular entity in the business domain, and mimic them with an architectural element.
c. A Service is conceived as a cohesive (and coherent) business functionality, technologically neutral, offered through a uniform interface. A Service is a plain, homonymous metaphor of a business service.
d. For an architecture, Orientation describes the guidelines, principles and decisions that are based on the rules that govern the metaphor behavior.
e. The Architecture refers to an actual style that defines the architectural constrains, suitability and consequences of using it.

From (a) to (e) :

SOA is an architectural style whose components, constrains and principles
are driven by the service metaphor.

2. Delta
By definition, and in contra-position from some usual implementation, SOA IS NOT:
a. An Indirection Layer for interoperability.
b. A Decoration Wrap for legacy code accessibility.
c. A Component from a whole that represents one architecture instance
d. A Service Group or container of services
e. A Business Process Container.
f. A Modernization Agent
g. An Object Distribution Technology
h. An Antagonist of REST
i. A ROI salvation
j. A Way of Life, A Philosophy of Doing or a Trend (It is an architecture style!)

Corollary of (j): SOA cannot be killed, it cannot just die.
It can be suitable for a problem or not.

By definition, and in contra-position from some usual implementation, Services ARE NOT:
a. Necessarily Web Services as defined in the WSA.
b. Ways to implement RPC nor RMI.
c. Exposed Methods or Objects.
d. Defined by the process they execute
e. Necessarily Stateless (YES, they should not necessarily be Stateless).

3. Principles.
Whenever there is the opportunity when working with SOA, people should
a. Favor Business Value exposed in the business domain OVER Business Value exposed with IT domain.
b. Favor Composability OVER Integration through Interoperability, AND favor Integration through Interoperability INSTEAD of Distribution.
c. Favor Metaphor rules INSTEAD of Tool rules
d. Favor Pure Document Style INSTEAD of RPC/RMI style. (NO WRAP TRICKS ALLOWED)
e. Favor Messaging OVER Other communication options.
f. Favor Business needs OVER specific IT practices (like optimization or flexibility)
g. Favor Entity documents OVER commanding documents
h. Favor Versionable documents OVER Structurally static documents.

So it is written.

William Martinez Pomares

In a recent discussion at InfoQ about the news of the upcoming SOA Manifesto, I had discussion with great people, including Jean-Jacques Dubray and Steve Ross-Talbot both renowned guys in the SOA world. We all talk the same, maybe at different levels or on different realms. Still, I promised Steve to put my two cents about SOA. Well, here I have a couple of ideas about it, too high level, but trying to clarify at least the three words that conform the acronym.

Well, here they go.

1. Many people talk about SOA and Services, but I’ve found in presentations, articles, case studies, working with tools vendors and looking at real implementations, that not everyone understands the concepts quite right. So, I have a couple of posts (here, and here) and a short video in the Architecture Journal (SOA Myths), explaining the types of perceptions people have about the concepts, and why I think they are wrong. I assure you it is a good list, interesting to read. So, that would be my first contribution.
2. Now, let’s check on the Service concept. As I mention in the posts, to me a service is a cohesive (and coherent) business functionality offered through a uniform interface. And it is technologically neutral. What does that mean? Well, a service is a plain, homonymous metaphor of a business service, just like the loan service in a bank, or a delivery service of you mail office. As a metaphor, it is driven by the rules of common services, with contracts, processes, protocols, controls and evolutions. Its actual implementation may be whatever, but it should not surface the definition, meaning users of a service do not have to know how the service was implemented to use it, and should not have to learn anything else apart from the rules and protocols of regular business services interactions.
3. Now, Orientation. For an architecture, orientation describes the guidelines, principles and decisions that are based on the rules that govern the metaphor behavior. That is, the service one.
4. Architecture refers to an actual style that defines the architectural constrains, suitability and consequences of using it.
5. So, SOA is an architectural styles whose components, constrains and principles are driven by the service metaphor.
6. Service implementation is out of scope. Service metaphor implies business domain. The implementation domain should not surface into the business view, not affect the rules of the metaphor. This is something almost all of implementation fails to accomplish: to use a service you usually must know implementation details, and those are the ones that actually avoid flexibility and change.
7. The service contract requires a semantic agreement (standard shared business semantics are a must), functional specification, pre and post conditions and the description of side effects. All that is technologically neutral.
8. Lastly, and just for the records: to me, reuse is not a business concept, but an IT one. So, Services should not have as a goal the reusable property. In business, the property is composability. The key is to be able to create higher-level services from composing lower level ones. Reuse is a side effect, and should not be the base for ROI, because it will never make it!

Hope this is clear.

William Martinez Pomares

From many talks, blogs, case studies and reviews, I have collected a list of conceptions of what people think SOA is.

Yes, Service Oriented Architecture may mean different things for different people. I’m not talking about definitions, since those are more academic-theoretical things. Conceptions are more like the practical being of the concept.

Most conceptions differences are subtle, but enough to be important.

Let’s star by saying I conceptualize a SOA (yes, an instance of a SOA) as an architecture whose elements, in majority, represent (or are) services. SOA is an architectural style.

That said, here is the list:

SOA as an Acronym. Yes, SOA is just a name created by composing the first letter from Service Oriented Architecture. Thus, SOA is taken as yet another acronym that may be compared to other named technologies. Just another one of the bunch.

Academic SOA. In trying to explain the concept, many academics find several similarities with other concepts they had known from long time ago. Are they simple exposed objects? Are services similar to Complex Systems? What is the difference between a Service and an Intelligent Agent? Of course, there are differences. Services were never meant to be exposed objects or components (although implementation made that happen). Complex systems have evolution, self organization, chaos is involved and emergence (clearly, services are far much simpler). And of course, an agent is something that is not only autonomous, social (talk to other agents) and react and pro-act, but also have intelligence. Services do not.

SOA as an Indirection Layer. Now this one is more on the earth of implementations. SOA is seen just as a layer that receives commands or requests, and passes them down to the real working objects (that ones with the business rules). So, SOA is just a way to add indirection to the requests, encapsulating and hiding the actual how-to. Of course, this conception is wrong by a great deal. SOA is not a layer to begin with. Being an architecture, it should be an organization of elements, the majority of them representing services. As implementation, we may think of services as the layer before the actual implementation, but the service is really the complete thing: the service contract, interface and inner implementation.

SOA as a Wrap. This is very similar to the above. SOA is seen just as a decoration for already made business logic. Usually presented as a salvation for legacy code, SOA is depicted in the diagrams as a layer that wraps the old in-use code, and made it usable for the new generations. (Careful with that picture, it is not as easy to expose old functionality with new interfaces, old code may not be designed to handle new load or business flow). Of course, SOA cannot be a wrap. You can create a wrap that uses services, but then your architecture will have new elements on top, services in the middle and old code down below. That is a sandwich, not really an architecture oriented to services.

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Through all these years, the service concept has been a confusing one. At the edge of Service Era, even before the service name was coined, services existed and were implemented using the tools at hand, and the tools helped to define the concept. I mean Services in all their presentations, those including SOA and Web Services, REST and CORBA, etc.

Today, after all this time, hundreds of articles, papers and news had been written explaining all facets of Services. Yet, many of them presented conceptual differences, and in the community’s mind a mix of myths started to grow.

The following is a list of myths I’ve encountered to be still present nowadays. Some are innocuous, some others are not. Furthermore, some may not be considered myths at all for all people, since their opinions may differ from mine. Anyway, here they are.

Myth 1: SOA = Web Services.
More that a myth, this is a general confusion enforced by tool vendors. Why? Because of selling SOA ready tools that offered Web Services construction, so conceptually having SOA was simply achieved by having Web Services
.
Reality: A Service is a bunch of functionality that is cohesively integrated into a locatable resource and accessed through a port using messages. (No, it’s not an object).

SOA is an architecture style that simply indicates the use of Services (special functional units) in the architecture. That is, you can have several very different architectures that are SOAs, with the common characteristic of having services in them.

Web Services Architecture is a special architecture that defines the description, interaction and messaging definition for a service that uses the web to communicate. Note that the service concept is part of both things, but Services are not limited to be Web Services. Web Services is just a way to create services. And Services may not use that architecture, nor be implemented trough the web.

Myth 2: Web Services = RPC.
SOAP (Simple Object Access Protocol) was born to make remote objects accessible through web. Its initial goals were clear: allow to encode a method call through web using XML. Later on, the service definition and concepts were improved, not limiting it to remote object method invocation but to a messaging system (even SOAP acronym changed to Service Oriented Architecture Protocol), but the “traditional” way of doing things kept implementing the services as simple remote method calls. In other words, a simple RPC.

The Service concept states the communication should be using messages, and those are all one way. If you want a request-response behavior, you need two messages: one in-one out. So, at the end, the services concept accepts RPC, but services are not RPC.

Martin Fowler states that difference in the book "Enterprise Integration Patterns: Designing, Building, and Deploying Messaging Solutions (The Addison-Wesley Signature Series) by Gregor Hohpe and Bobby Woolf", when he writes about integration by sharing. RPC is good to share functionality, but services will help to share functionality and data, and they are the less coupled form of integration.

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Paul kindly pointed to a blog entry about WADL use in REST, (WADL definition is found here). The Blog entry was interesting to read.

I want to quickly explain that WADL is meant to describe the possible interactions with a Web Application. Thus, it has methods, but those are HTTP commads, and it also describes the query variables (like the fields in a form) that the method needs to send to the web application. Finally, it describes the expected response.

Now, in the blog I see some misconceptions. First, it relates SOAP and WSDL to XML-RPC. That may seem true due to actual use of those two, but SOAP is just a wrapper and WSDL does not enforce XML-RPC, using document/style it reassembles a simply document sending paradigm. By the way, XML-RPC and WS used to do RPC are two completely different things.

Second, the REST based Service concept is defined to encompass even static web pages. May REST style architecture handle resources in the web, and REST “style” Services are services implemented using the REST underlying paradigm. But Static pages are not Services.

Third, WADL is at implementation level of the HTTP call, thus it does not define the service, just what to call and what to expect in response. That is not bad, it is actually good, but then WADL describes an HTTP interaction, while WSDL describes a messaging interaction. Although not actually standardized, WSDL may allow you to send messages using a message queue, SMTP, or any other transport.

Now, I want to explain my vote. I’m not a WSDL lover, I think it may be improved. Still, I’m carefull to compare, it is not as easy. We cannot say WADL is a description document for REST based Services and WSDL for RPC based ones. Right?

I may want to go even further. I may say REST Style Services may actually make use of both! Yes, while WSDL describes your Service at message level, defining the document and port, and a WADL that makes clearer the HTTP interaction (since WSDL inly indicates you are using HTTP as a transport).

Again, what do you think?

William Martinez Pomares.

I a recent comment, Paul mentions he is not familiar with the Document Style concept. This is a great opportunity to touch the theme and clarify some ideas about WSDL and the WSA idea of a service.

WSDL is meant to describe the service definition and interaction models. WSDL defines:

• The Service’s visible endpoint. That is, the address where the port of the service leaves.
• The Binding. That is, which transport to use and how.
• The Operations. Each operation with a name and a message flow (a named message inbound or outbound).
• The Messages. Each named message has a number of named parts that conform the payload.
• The Parts. Each one is defined either by indicating the primitive type or a schema defined xml.
• The Schema. A Types section that is defined using an XML schemas.

Using the above sections, we can define the service by indicating the port, the available operations, which message flow each operation has, and what is the structure of each message.

With the WSDL, the client is able to know how to construct the message and where to send it. So far so good for our service notion.

The problem comes when WSA came out with the style/encoding idea. SOAP was originally created to access Objects remotely (Simple Object Access Protocol). Here is the story.

Those were the times when RPC was the idea of remote access. So, SOAP was created a requirement for the body of the message. It had to be constructed with a fixed structure, where the root element’s name should be the same as the method name. The children elements should be one per parameter, and each one containing the type as an attribute. That structure was known as the encoding.

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Based on several comments and articles I've read, I tend to think that SOA and Web Services are being misunderstood. Maybe I’m the one that is wrong, but just in case I will try to explain here what I understand. I guess the first thing to do is to define what a service is.

Base on the Web Service Architecture specification, a service is “… an abstract resource that represents a capability of performing tasks that represents a coherent functionality from the point of view of provider entities and requester entities.”

I want to point out the fact that a service is a “resource”, it can perform some tasks, and it represents functionality. A service has an ID that will let us find it in the networking cloud. It has a description and it has an interface. That interface “… is the abstract boundary that a service exposes. It defines the types of messages and the message exchange patterns that are involved in interacting with the service, together with any conditions implied by those messages.”

Let’s put it in other words. A Service is a coherent functionality offered by a web resource. To communicate with it, you use its interface. It will accept messages interchanged in a predefined pattern.

But there is an important fact: “To be used, a service must be realized by a concrete provider agent.”, WSA spec says. In other words, a service is an abstract model of a resource. That functionality is to be realized by a concrete agent, may it be software or hardware. Let think of it as a functional cloud, accessed by messages delivered to a port.

An Example may help.

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I just wrote an answer in TSS that I thought I could share here too. The basic idea everyone has about services is that they are to distribute logic, make remote calls, have loose coupling interfaces, and are resusable. And nothing is working as it is advertised. I will play the defendant part here.

“I see a repeating idea about SOA, services in particular, that doesn’t fit in what I have learned from my childhood as an architect. I will explain myself.

I recall the old Object oriented days when all the fuzz was about reusability. The idea was clear: separate the code into coherent and functional complete things. Then a problem was found: the interface. You could not reuse the thing because of the interface not being suitable, or requiring things not in the new problem domain.

Then a service came. It was the idea of having a business functionality (not an interface, not an object) able to accept messages and offer a business value. It has no reusability concept, the fuzz was actually about replacing fixed interfaces with a simple port. And somebody said: Let’s implement it with SOAP. And SOAP was Simple Object Access Protocol, an RPC oriented wrapping protocol used to access distributed objects. Wow. Wait a minute. Something is not working here. I know objects were supposed to accept messages. Nobody uses that. But a service is not an object. A service has no methods or parameters. Definitively, it has no response. There is no interface per se, just a port where you deliver your message.

Now, the message is not SOAP. SOAP is a wrapper. The real thing is in the body.

Once the service has read from the port the message content, it will now know what to do. And it may decide to send another message. As simple as that. But as difficult to grasp for an object programmer, that it was reduced to a YAMTCARO (Yet another method to call a remote object).

NOw, can somebody tell me why a service needs a method name to be called? SOAP had stubs in the client, to simulate the remote object as local. Services are not object, stubs have no place here. Makes no sense. You need a port object to stream your message. Simple.

Finally, since a service is just a port, and the service semantics (which are not technically describable) is hidden behind the service cloud. You can create a versioning system underneath the cloud, so old messages can still be accepted and new messages, that represent new business needs, be processed as required. Service cloud still as white as before. It may have a new port, but old ports may be still there.

Enterprise architects? Their job is to have one eye in the problem space, and the other in the solution space. They will work with business people to design services scope (business driven), and work with designers to technically create the structure of the cloud.

Hope this helps to understand why I say all that I say.”

William Martinez Pomares

Funny article in SOA Masters Class site. It explains the vision of SOA based in two variables: the Architecture involvement scope, and the Service concept scope.
Yep, there is a big difference when you see the Service concept as an exposed component, or as business functionality. Same for involving the architecture simply as a glue to interoperate disparate systems, or as a business driven structure.

Funny indeed!

William Martinez Pomares

Hi All!

Very excited that I’m writing my very first post in the blog.
And since this is an Architecturing blog, I thought I could point it to a very interesting discussion held at The Server Side.

The article presented here is about the complexity generated when using SOA, compared to the same complexity history of CORBA times. Although the idea is nice, most of the participants show a problem of understanding what SOA really is.

System Integrator Technology? CORBA with a new acronym? A new distributed approach to organize business logic? Simple EJB, SOAP and other technologies follow up, with nothing new? No several times.

As I mentioned in my responses there, SOA is based on the service Metaphor, which is placed in the problem domain, problem space, where business organization rules and not technology trends. SOA now is a patched, almost like a stovepipe architecture, solution for integration, and like that it sells.

Later I will write a little bit more about the Service metaphor. That is not for RPC developers, I’m sure.

William Martinez Pomares