The ObjectWatch Newsletter
Now In Our Tenth Year
A Quarterly Newsletter for
Software Architects
by Roger Sessions
Issue # 49 - February 2005
This
newsletter is sponsored by
The International Association of Software Architects provides a forum for business, technology and systems architects to share knowledge about application architecture, multi-systems architectures, vertical and horizontal re-use strategies, architecture methodologies and strategies, and architecture definitions.
www.iasarchitects.org
Table of
Contents
Quotation
of the Month: Our Government At Work
ObjectWatch
Architect Technology Advisory (ATA)
Quotation of the Month: Our Government At Work
"I did not get what I
envisioned" from the project, the senior official acknowledged. But he
said the F.B.I. today had a better understanding of its computer needs and
limitations as a result of the effort. "The lesson we have learned from
this $170 million is invaluable," he said.
- An unnamed senior official of the FBI explaining why the FBI spent $170 million on a computer system, once deemed critical to the war on terrorism, that is now described by the FBI itself as “unusable”, in F.B.I. May Scrap Vital Overhaul of Its Outdated Computer System By Eric Lichtblau, New York Times, January 14, 2005
The winner of the Quotation of the Month Contest is Martha Reilly
who gets a choice of a personally autographed copy of Roger Sessions's book, Software Fortresses: Modeling Enterprise
Architectures, or the ObjectWatch BBQ apron. Send in your nominations for
Quotation of the Month to
The Rings of the Enterprise
by Roger Sessions
Many readers of The ObjectWatch Newsletter know that my
favorite place to sit while writing is the big comfy chair in the corner of the
Starbucks at 183 and
There are many reasons I order this particular drink. I like it. It’s cheap (well, by Starbuck’s standards, anyway). It is intense. It is crawling with caffeine.
But on a recent trip to Starbucks, I discovered a new reason for ordering a Doppio Macchiato. It’s illegal not too! On that trip, I was followed by our local Sheriff who was prepared to pull me over and give me a ticket if I didn’t go into the Starbucks and get my favorite drink.
How is this possible? It might help to understand how my
favorite Starbucks is situated. Figure 1
gives a map showing my Starbucks with the dotted line showing my path as I
meander in from
Figure 1. Starbucks Map
Notice how close the Starbucks is to the 183 plaza entrance.
Now it turns out that some unscrupulous people take an almost identical path to
mine, except that at the last minute they don’t turn into Starbucks, they leave
the plaza at the 183 entrance. In other words, they could care less about a
Doppio Macchiato. They are trying to avoid the traffic at the corner of 183 and
So when the Sheriff, who was in the car right behind mine on
If you think about this, you will realize that there are four distinct geographic regions arranged in concentric circles all emanating out from the counter of Starbucks. These circles are shown in Figure 2.
Figure 2. The Starbucks Rings
Ring Zero is the innermost ring. This is the space behind the counter at Starbucks. I don’t know what goes on there because I am never allowed behind the counter.
Ring One is the second ring. This is the space inside Starbucks. This is where I wait for my order, side by side with the rest of the shivering, huddled masses waiting for their drinks.
Ring Two is the third ring. I know this sounds confusing because I started counting with zero. But try to stay with me here. The third ring is the shopping plaza in which the Starbucks is located.
Ring Three is the fourth ring. This is the rest of the
world, the area outside the plaza. For purposes of this discussion, Ring Three
is
Notice that each ring has its own rules and regulations. For example, Ring Three. If I had stayed in Ring Three (outside the plaza), the Sheriff never would have followed me. In Ring Three there is no law that you must get a Doppio Macchiato. This is why I avoid Ring Three whenever possible.
Once you enter Ring Two, you are accepting a new set of rules and regulations, namely, you are now required to buy a Doppio Macchiato. Maybe you are allowed to buy something else. I don’t know. I have never tried.
From here it is a short hop to Ring One. Now you are inside Starbucks and under a whole new set of rules. These rules govern issues like ordering, standing in line (forever, it seems), and paying, issues that nobody in Ring Two cares about.
I assume that Ring Zero (the barrista ring) has its own set of rules, such as when you must show up for work, when you are allowed to leave, and so forth. Like I said, I’m not allowed in Ring Zero, so I wouldn’t know.
It’s not just the Doppio Macchiato (or lack thereof) that differentiates ring from ring. There are also rules that govern movement. In Ring Three, I am allowed to drive my car up to 60 miles per hour. In Ring Two I am still allowed to drive my car, but now my speed is limited to 10 miles per hour. In Ring One, I am not allowed to drive at all; I am forced to abandon my car and walk. In Ring Zero, there is very little lateral movement at all, mostly just arm waving and shouting.
You can see that ordering a Doppio Macchiato is not as simple as it seems. It requires a detailed understanding of the Starbucks Ring Structure, a knowledge of which ring you are in at any given time, and a full grasp of the rules that govern life in each one of those rings. If I try driving my car into Ring One, for example, I will be in serious trouble, even though such an activity is encouraged in Ring Three.
Most people might have a difficult time understanding and grasping the significance of the Starbucks Ring Structure. As it turns out, I find the whole concept very intuitive. I would like to believe this is because of my advanced intellectual capability. In reality, it is because I have already seen a very similar ring structure, that of enterprise software systems, and especially enterprise software systems using Service-Oriented Architectures (SOAs). Since SOAs happen to be my particular specialty you can see that I have somewhat of a unfair advantage in navigating the Starbucks rings. The rest of you may have a little more trouble ordering your Doppio Macchiatos.
In an effort to help you better understand the Starbucks rings, I’m going to take some time to explain the SOA rings. Since most of my readers are technologists, I assume that SOA rings will be easier to grasp than Starbucks rings. Once you understand the SOA rings, you should be able to extrapolate what you have learned to the Starbucks rings and order your own Doppio Macchiato.
As you probably know, an SOA is an approach to interoperability between autonomous business systems, specifically autonomous business systems that are packaged as services. A service is an autonomous business system that is able to accept SOAP requests and whose interoperability is governed by the various Web service standards. The most important of these standards I covered in the November 2004 ObjectWatch Newsletter.
A typical enterprise has a number of these service, each one of which has a four-ring structure much like the Starbucks system. The enterprise rings are shown in Figure 3 which you can compare for similarity to Figure 2. Let’s go through the Enterprise Rings, one by one.
Figure 3. The
Ring Zero is the implementation of the service. This is where we have distributed components, processes, and armies of objects running around and doing their thing, together implementing a shipping service, a credit-card-authorization service, or whatever business functionality this particular service happens to implement.
Ring One is the collection of other services in the enterprise. A retail operation may have a point-of-sale service, an inventory service, a customer-management service, and any number of other services, each of which plays its role in the overall operation and each of which needs to interoperate with the other enterprise services.
Ring Two is the collection of services outside the enterprise that needs to collaborate with one or more of the enterprise services. This might include supplier services and banking services.
Ring Three is the rest of the world. This is the riff-raff we want to have nothing to do with.
Like the Starbucks rings, each of these rings has its own rules for how things are done. Take communications, for example. Communications with Ring Three is strongly discouraged. Communications in Ring Two will mostly be done asynchronously using the reliable messaging protocol I discussed in the last ObjectWatch Newsletter. Communications in Ring One will also be asynchronous, but now will use a proprietary message queue system. Communications in Ring Zero is totally different. It is not asynchronous at all. It is synchronous, proprietary, and focused on speed.
Security is another issue that differs markedly as we move from ring to ring. Security at Ring Three is primarily based on firewalls. Security at Ring Two will primarily be based on the new Web-service security protocols that I discussed in the November issue of the ObjectWatch Newsletter). Security at Ring One will be based more on secure transport. And once we enter Ring Zero, security is no longer an issue.
Some issues are specific to certain rings only. Implementation of business functionality, for example, is strictly a Ring Zero issue. The rules that govern service implementation must be followed very carefully, if the service will be able to properly interact with other services. (I discussed the Ten Rules of Implementing Services in the February ObjectWatch Architect Technology Advisory). These rules must be well understood and assiduously followed, but they are only important inside Ring Zero. Once you are outside Ring Zero, these rules are no longer relevant.
Understanding the Enterprise Rings can help us focus our product comparisons. Consider a group trying to decide between using Microsoft’s C# and IBM’s Java for doing development. Should this decision be made at the project level or at the enterprise level?
Both C# and Java are Ring Zero technologies. In other words, they are technologies that are used to do development inside a Ring Zero service. Since their impact is limited to Ring Zero, there is no reason the decision between C# and Java needs to be made at the enterprise level. Each Ring Zero group (say, the group implementing the Shipping service) can choose the programming language and software platform that works best for its project.
On the other hand, what about the decision between MSMQ and MQSeries, two message queue technologies? Message queues are Ring One technologies. Their is no reason the Ring Zero implementers would be impacted by the MSMQ/MQSeries choice. This decision needs to be made by the enterprise infrastructure architects who specialize in solving Ring One problems.
As you develop your enterprise architecture, the Enterprise Rings can be an important aid in understanding relationships between systems, choosing technologies, and codifying contracts.
And, of course, now you can much better appreciate the Starbucks rings. Let me know if you need any more help. In the meantime, I’m heading out for a Doppio Macchiato. Maybe two. After all, it’s not just a drink. It’s the law!
- Roger Sessions
ObjectWatch Architect Technology Advisory (ATA)
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