### Introduction

We (Richard Hubert and Roger Sessions) have a lot in common. We are both Fellows of the International Association of Software Architects (IASA). We have both written books and articles. And we are both well known proponents of a particular approach to Enterprise and IT Architectures. For Richard, this approach is called Convergence Architecture. For Roger, this approach is called The Snowman Practice. But it may turn out that we have more in common than we thought. Our approaches may complement each other in some interesting ways. But first, let’s take a look at what each of us has been doing.### Introduction to Richard’s work

Since the mid 1990’s I (Richard) have been developing and optimizing an architectural style that addresses the complexity of both the IT systems and the business processes. I call this holistic perspective Convergent Architecture (CA). I wrote about this in 2001 in my book Convergent Architecture (John Wiley N.Y. ISBN: 0471105600.) CA includes properties that I consider to be inherent in any architectural style. The metamodel that I use includes the project design, the system design, and the business design. At a high level, this model is shown in the following diagram:

Figure 1. Coverage of a holistic architectural style

As you can see in the above diagram, the partitioning between Organization, Process, and Resource plays a significant role in the quality of the design. Experience and rules-of-thumb are adequate to handle many designs, but as systems get larger, a more formal approach is preferable, especially if it can be assisted by tools. This is where Roger’s work is a perfect fit.

### Introduction to Roger’s work

I (Roger) have been looking at how to validate an architecture. To do this, I have developed a mathematical model for what an ideal architecture looks like and a methodology for delivering an architecture that is as close to that ideal as possible. The starting point for this is to define what we mean by “ideal.” My definition of an ideal architecture is the least complex architecture that solves the business problem. This means that we also need a metric for measuring complexity, which, fortunately, comes out of the mathematical model. You can read about this mathematical model in this white paper.

It turns out that when you discover the ideal architecture for a given problem, it almost always has a characteristic shape: A collection of business functionality sitting on top of a collection of services sitting on top of a collection of data. In addition, these three tiers are separated from other collections by strong vertical partitions. There is a strong connection between business functions in the top tier, services in the middle tier, and data in the bottom tier. Where connections are required between tiers, these occur through asynchronous messages at the service level. This architecture is shown in the following diagram:

Figure 2. The Snowman Architecture Created By SIP

As you can see in the above diagram, the idealized architecture looks a lot like a snowman. The head, torso, and bottom of the snowman contain business functions, services, and data, respectively.

The methodology I (Roger) have developed to drive this architecture is called SIP, for Snowman Identification Process. Some of you may know it under its old name, Simple Iterative Partitions. You can get a good overview of The Snowman Practice from this video.

### Synergy discovery

When we compared the architecture that is driven by the CA’s architectural metamodel (Figure 1) to the architecture that is driven by the highly theoretical SIP (Figure 2) it was clear to us that significant commonalities are at hand.

Both approaches are based on the fundamental Enterprise Architecture principle of IT-Business alignment. Both approaches define best practices concerning how this alignment can be effectively achieved and measured. Additionally, both approaches are based on rules and patterns that apply to the simplification of any system, whether large or small, organizational or purely technical. The Convergent Architecture, for instance, has been used to design IT-organizations which then use the same approach to design and simplify IT systems (this is conceptual isomorphism).

Lastly, and most important of all, we recognized a SIP approach can be applied to mathematically support and objectively drive both architectural styles. SIP thus enhances the design approach and process as both a tool and substantive mathematical proof needed to ascertain the simplest (least complex) of all possible system and organizational structures. .

In essence, we now have CA showing that the SIP theory really does deliver a partition that stands up to the most demanding examination. And at the same time we have the SIP mathematics defining the vertical boundaries of a CA architecture that are mathematically not only sound, but as simple as possible.

### The Future

Where will this take us? To be honest, we are still discussing this. But the possibilities are intriguing. Imagine, two mature methodologies that have such strong synergy where both the theoretical and the model-driven approaches seem to come up with such complementary solutions. Stay tuned for more information.

## 2 comments:

Good blog Roger. I definitely agree that the ideal architecture is the simplest and I am keen to see how you might be measuring them. Perhaps it is as simple as using the maths in your white paper.

I am interested though in why business rules are not represented in your architecture. Some good work has been done by the OMG in showing that business processes, rules and data are as important as each other and need to be represented in any architecture. Rules are often where complexity grows.

Tim

Tim,

Thanks for your comment!

Good question, about the Business Rules. They are certainly important to understand in any robust architecture.

They are somewhat represented in The Snowman Architecture. They are the head of the Snowman and dictate the partitioning at the lower levels.

However I don´t spend much time on Business Rules for a few reasons:

- Business Rules are well dealt with by other groups, such as OMG.

- The Snowman Architecture is concerned with the shape of things, not how things are implemented

- Architectural complexity is only marginally related to Business complexity. For example, I looked at a number of banking IT systems that had showed severe reliability problems. In all cases, the business architecture was very straight forward and the reliability issues were clearly related to Architectural Complexity.

- Roger

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