utree - Utility Trees
A utility tree is a picture that helps articular architectural qualities for a particular system. When faced with general terms like "scalability", "security", "performance", "modifiability", and so on, a customer's only possible response is, "Yes, please. I'd like some of those." It doesn't help to ask which one is more important. The problem is that those terms are too abstract.
A utility tree lets you get down to brass tacks, by talking about concrete "quality scenarios". A single quality scenario will be attached to a facet of a quality. It should be measurable and quantitative.
To learn more about utility trees, take a look at "Evaluting Software Architectures", by Clements, Kazman, and Klein.
This uses Leiningen 2 to build. Run all of these from the base of the project.
To build a standalone jar file:
Run from the command line:
java -cp `lein2 classpath` utree.core _command_ _command-options_
Alternatively, you can build a standalone jar and run that directly: lein2 uberjar java -cp target/utree-0.0.3-standalone.jar command command-options
- dot - Turn a utility tree into a dot graph for making images.
- radar-plots - Render radar plots as PNGs for the solution alternatives in the input file.
java -cp `lein2 classpath` utree.core dot _filename_
Use filename as the input file (format below).
java -cp `lein2 classpath` utree.core dot sample.ut | dot -Tpng -osample.png
Use filename as the input file. Render PNGs named
java -cp target/utree-0.0.3-standlone.jar radar-plots example/alternatives.ut
This will create solution_0.png through solution_3.png, showing how the different alternative solutions score on the axes that matter.
Pictures don't version control well. I wanted a text-based format that would work well with all our other project artifacts.
The input format is a text file, consisting of one or more sections. Each section is marked by a header: a line starting with 2 or more hypens and a section type.
-- Utility # Quality attribute lines follow -- Alternatives # Solution alternatives follow
Quality attribute lines start with asterisks. These will appear in the output diagram. The number of lines indicates that attribute's nesting level. There is no line-wrapping.
* Availability ** COTS Software Failures ** Hardware Failure *** Power outage at site 1 requires traffic redirect to site 3 in < 3 seconds. *** Restart after disk failure in < 5 minutes. *** Network failure is detected and recovered in < 1.5 minutes.
If you want to add comments, version control IDs, or extra text, feel free. Other lines will be silently ignored.
Ranking and Weighting
You can add explicit ranking within a group of quality attributes by adding a number inside of square brackets. These ranks eventually get turned into relative weights for each quality attribute.
*  Availability **  Hardware Failures ***  Power outage at site 1 requires traffic redirect to site 3 in < 3 seconds. ***  Restart after disk failure in < 5 minutes. ***  Network failure is detected and recovered in < 1.5 minutes. **  COTS Software Failures *  Security **  Confidentiality **  Integrity
The reason for adding ranks explicitly, rather than just computing them based on the sequence is so you can capture the scenarios in one pass, then come back and rank them in a second pass, without having to shuffle lines and sections around. (Yes, I know that Emacs outline mode makes this easy. I use it, but I'm not going to force it on everyone. That would be cruel... some people just aren't cut out for Emacs.)
The ranking at each level influences ranking of the child elements. In the example above, "Hardware Failures" is ranked first of two, so it gets a weight of 0.75. Security is second of two, so it gets 0.25. Then within the hardware failures attribute, we have 3 scenarios. The top ranked item "Network failure..." gets a local weight of 0.61111... times its inherited weight of 0.75 for an overall weight of 0.458333... The second ranked item has a local weight of 0.2777... times its inherited weight of 0.75 for an overall weight of 0.2083...
These weights can then be used in a decision matrix to evaluate alternative solutions. When considering several architectures for a system, you can rate each architecture relative to how well it supports the quality scenarios. Multiply the ratings by the weights computed here, and you'll have a weighted score for each alternative.
See James McCaffrey's blog post about computing rank-ordered centroids. See also dot-utility.graph/roc for an implementation.
Rank-ordered centroids are used in LAAAM (full support coming soon here!), which is an architecture-focused instantiation of the Analytic Hierarchy Process.
At this time, weights only appear as annotations on the quality scenarios. Watch this space for more.