Charlie Alfred's Weblog

Relating Quality Attribute Scenarios to Contexts and Challenges

charliealfred — Mon, 05 Dec 2011 01:31:08 +0000

Quality Attribute Scenarios were popularized by the Software Engineering Institute in the early 2000’s, in the book, Evaluating Software Architectures by Rick Kazman, Paul Clements, and Mark Klein. A quality attribute scenario associates a stimulus, and a set of environmental conditions with an expected outcome of the system whose architecture is being evaluated. Quality Attribute Scenarios are commonly organized in a Quality Attribute tree.

Contexts and Challenges are topics written about in other pages in this blog:

Over the past several months, I have observed several product managers, architects and engineers misapply quality attributes, quality attribute scenarios, contexts and challenges. While these concepts are closely related (even to the point of some overlap), the nuances driving their distinctions are important. In http://charliealfred.wordpress.com/quality-attributes-contexts-and-challenges/, I will try to clarify the relationship between these two useful sets of concepts.

Invisible Requirements aren’t Invisible, Just Obscured

charliealfred — Wed, 25 May 2011 11:11:39 +0000

At one time or another, all people are concerned about the unknown, especially the unknown-unknowns. It happens frequently while driving a car. You change lanes and don’t see the car that’s in your blind spot. Or, you are on a business trip, driving at night, and your GPS tells you to take a left on a street that is one-way to the right. If it wasn’t dark, you might be able to find a landmark to regain your sense of direction.

Business executives, product managers, architects, and engineers are not immune to the unknown-unknowns, in spite of our years of experience and depth and breadth of knowledge. We write requirements for a new product. We’ve talked with our key customers. We understand what they want. We have them reviewed. After a few discussions and suggestions, we leave the room agreeing that this is what needs to be done. Let’s get started! Sure, there are uncertainties, but nothing we haven’t handled in the past. But the ”invisible requirements” are there waiting – the unknown-unknowns.

The article on Invisible Requirements, at http://charliealfred.wordpress.com/invisible-requirements/, is a white paper that I co-authored with Garrett Thurston. Thanks to Tim Bowe, CEO of Foliage for giving me permission to republish it. This paper has a similar theme to a paper I wrote a few years ago, titled Requirements vs. Architecture (http://charliealfred.wordpress.com/requirements-vs-architecture/) , but looks at the problem from a different angle. Hopefully, it will act like a flashlight and give you a few techniques for illuminating those invisible requirements that stand in the way of your product development effort.

Charlie

Architecting multiple context systems

charliealfred — Sat, 27 Mar 2010 22:18:51 +0000

Today, many systems need to be designed to work in many different contexts. Consider GPS technology as an example. GPS receivers support a wide range of applications, from driving to hiking, to the autonomous operation of farm or mining equipment. The needs for accuracy and availability vary widely across these applications. In addition, GPS receivers must be designed to operate in a variety of weather conditions, with a variety of natural and man-made obstructions. How do you balance these benefits and challenges if you are designing software that uses GPS technology?

A context is a collection of stakeholders who share a similar set of perceptions, priorities, and desired outcomes, and who are subjected to a similar set of conditions and forces. In the above example, different GPS applications contexts include: a) autmobile drivers, b) hikers, c) boaters, d) automatic farm equipment (e.g. unattended corn or wheat harvesters), e) automated ore removal vehicles in mines, etc. Automated farm equipment or mining users need accuracy of a few feet. Automobile drivers require enough precision to match them to the correct road. Hikers often hike in forests or canyons which block signals from GPS sattelites.

When applications are deployed in a single context, environmental conditions and stakeholder perceptions usually converge, and this convergence helps to resolve tradeoffs. However, whenever multiple contexts come into play, the tradeoffs are less clear and the design decisions become more difficult. The following article, http://charliealfred.wordpress.com/multi-context-systems/ recently published in Issue 23 of Microsoft Architecture Journal provides some thoughts about how to address this type of problem.

Putting the Proposition back into Value Propositions

charliealfred — Mon, 19 Oct 2009 00:25:55 +0000

Value Propositions are as to marketers, as Gannt charts are to project managers or debuggers are to software developers.

But value propositions can and should be more than marketing hocus pocus. What value propositions promise, imply, conditionally promise, or avoid mentioning at all are a reflection of what is important to the business. This conviction works its way into philosophies of product design and priorities for organizing and staffinf up service operations.

This article (http://charliealfred.wordpress.com/value-propositions-more-than-marketing/) will explore the nuances of value propositions, with some modern day examples to illustrate the points.

SCRUM and Architecture – Do they mix?

charliealfred — Mon, 07 Sep 2009 01:08:17 +0000

SCRUM is a popular agile development methodology that was first popularized in the early 1990′s by Ken Schwaber and others. It features short (2-3 week) development sprints, development team accountability, and separation of the chickens (management stakeholders) from the pigs (developers).

Software architecture is a high-level approach to the conception of a system. It was initialy popularized in the mid 1980′s by the writings of David Garlan and Mary Shaw. The Software Engineering Institute (SEI), affiliated with Carnegie Mellon University has been a major force in spreading the software architecture mantra. Today, virtually every software development group of 12 people or larger has a software architect on staff.

However, during the past 20 years, SCRUM and Software Architecture have lived a somewhat tenuous existence. Like other agile methods (such as XP), SCRUM is not a believer in big design efforts up front. Planning mainly consists of choosing a team, and capturing and prioritizing a number of user stories. From that point, the development team and product manager select the set of stories to work on during each sprint, and the developers figure out how to design the solution.

The SCRUM methodology is intended to have fast reaction times to changes in requirements or priorities. During a sprint, no course changes are permitted, but between sprints, anything goes. If the changes are significant, the development team relies on refactoring existing software and leveraging automated unit tests to ensure no regressions.

This article (located at http://charliealfred.wordpress.com/scrum-and-architecture-partners-or-adversaries/) explores the relationship between SCRUM and Software Architecture, primarily from the perspective of a recent project that tried to blend both.

Architecture Core Concepts

charliealfred — Sun, 29 Mar 2009 12:11:04 +0000

Around two years ago, I started writing a blog on value modeling and architecture. The results of this effort are posted in the pages of this blog. I will be taking a hiatus (hopefully brief) from my writing – predominately due to time constraints. So, I thought it would be useful to wrap up with a summary page, one that attempts to capture the concepts that I think are essential to all software architects (and quite possibly other types of architects, too). In the following page, I identify 8 core concepts and describe each with a short paragraph. Following the paragraph, I include 2 or 3 links to other articles in this blog that expand on that concept, for anyone looking for more information.

12:26 PM 3/29/09: Added a new diagram and paragraph to the summary

http://charliealfred.wordpress.com/architecture-in-a-nutshell/

More Conceptual Distance

charliealfred — Sat, 21 Mar 2009 17:08:43 +0000

Most of us have watched our retirement portfolios and children’s college funds shrink by 50% during the past six months. As painful as this is, there are lessons to be taken away. No, I’m not referring to the people who want to lynch those who received million dollar bonuses from AIG. And I’m not even referring to the people who now want to regulate anything that moves.

No, I’m talking to the people who want to understand some of the fundamental causes, and think about how little understanding of the risks caused by the real underlying factors actually made it through the “split pea soup” we happily call communication in our day and age. How will the world function when information that must be conveyed won’t fit in a cell phone text message?” Do we coast merrily along hoping that our surface-level assumptions hold water? Or do we cross our fingers and hope that the other guy has the answers (then point an appropriate finger when things go wrong)?

I don’t profess to know the answer here. Too much depends on the fickleness of human behavior. But I think that the excellent March 2008 article in Wired, written by Felix Salmon, is a great place to start, and I hope that the article that appears in http://charliealfred.wordpress.com/conceptual-distance-and-the-2008-market-meltdown/ helps to frame it properly.

Pattern Languages

charliealfred — Sat, 21 Feb 2009 18:05:30 +0000

It has been 32 years since Christopher Alexander wrote A Timeless Way of Building, and 15 since the Gang of Four wrote Design Patterns. Today, virtually everybody working in software development can tell you what a Singleton or a Factory is. And that is a very good thing. But, is it enough?

Christopher Alexander talks about the preeminence of a pattern language — a system of interrelated patterns that combine and synergize to resolve all of the forces in the larger context. No matter how large your catalog of design pattern is, you don’t have a pattern language until you knit them into a system. Sure sounds like architecture to me!

The following essay (http://charliealfred.wordpress.com/200/) explores Design Patterns, A Timeless Way of Building, and several related topics to try to understand how, as an industry, we can start putting the language back into pattern languages. And along the way, we identify a North Star, for those who believe that pattern languages are an important step in the maturation of software development.

Seven Deadly Sins

charliealfred — Sun, 18 Jan 2009 20:13:05 +0000

Most of us are familiar with Dante’s “Seven Deadly Sins” – lust, gluttony, sloth, greed, envy, pride, and wrath. And many of us remember the vivid depiction of these sins in the movie Seven.

Imagine if Dante were alive today. What might he have to say about the state of software product development? Few would doubt that this activity has its own special collection of aberrant and deviant behaviors. Perhaps the sins of software product development aren’t as intentional as the original set, but they sure can impete and frustrate the best efforts of those of us who work in this space.

So, the article http://charliealfred.wordpress.com/seven-deadly-sins-of-product-development/ is devoted to exploring the Seven Deadly Sins of Product Development. It was fun to write. I hope it is enjoyable and informational to read.

My two-cents about architecture style

charliealfred — Sun, 21 Dec 2008 22:16:14 +0000

Recently, the topic of architecture style has gotten more discussion. A colleague, Ruth Malan, noted that the Microsoft Application Architecture guide has devoted a chapter to the topic. Ruth contrasted their definition with the one she published in her blog in July 2008. In addition, architecture giants, such as David Garlan, Mary Shaw, and Roy Fielding have each weighed in with their own definitions.

So why does this matter? Why should a practicing architect care who specifies which definitions and whether or not they are consistent. Does anybody’s work day really depend on a definition?

Personally, I think it can. But I don’t really think it’s about the definitions anyway. I think it’s about identifying, clarifying, understanding, and discussing the concepts that underlie the definitions.

At the end of the day, I think that a clear picture of what architecture styles are, and how they relate to architecture formulation, is extremely important for all practicing architects. If you are skeptical, take a few minutes to read my article at http://charliealfred.wordpress.com/architecture-stylin/ and leave a comment to let me know if you agree or disagree.