Trouble With Your Object Oriented (OO) Design? Are You Obeying the Single Responsibility Principle (SRP)?

October 22, 2008 By Mead Matthew Leave a Comment

The Single Responsibility Principle (SRP) is defined by wikipedia as every object should have a single responsibility, and that all its services should be narrowly aligned with that responsibility.

Although the origins of this concept are someone disputed, most believe it was originally developed by Tom DeMarco in his book Structured Analysis and Systems Specification but was later popularized by Robert Martin in his book Agile Software Development: Principles, Patterns, and Practices. The principle simply states that a given class should have one and only one responsibility. And that the behavior of the class should be narrowly aligned with that single responsibility.

The essence of this concept has to do with the reason to change a class. If a class has more than one responsibility, it may have different reasons to change, each of which are independent of one another. Take for example a class that both imports data from a file and saves the data to a persistent storage mechanism. The single class needs to be modified for any change to the incoming file format as well as any change to the underlying data storage mechanism structure. These changes should not be connected. By modifying the class to adjust the file format, you risk introducing a bug to the file persistence code. In a hurry, without the safety net of automated unit tests (gasp!), developers tend to only test code that is related to a given change.

If your classes follow SRP, you probably can get away with only testing related code (although thorough automated unit tests are always the best course of action). If you violate SRP, you need to be extra cautious when considering the ripple effect from changes to your code. I believe SRP is so fundamental that it can make the difference between a system that is easy to maintain and one that is your worst nightmare to maintain.

Sounds simple right? Well it is, but it is common while designing and refactoring to find SRP violations. But let’s face it. Most software stinks and I have seen countless convoluted designs. Many of these designs (not designed by me of course) had a systemic SRP issue. SRP in one class in your system is not big deal, but SRP in most of your classes is sure recipe for disaster and a system that is very difficult to maintain.

When I have difficulty getting a design to feel right, I try to ask myself whether the classes in that portion of the system are following SRP. Many times, I find the core design issue stems from one or more classes with more than one responsibility.

There are many ways to deal with SRP violations. The most common are:

Delegation – To put behavior in another class and leverage a pattern such as Strategy
Aggregation – To push the behavior out to another class and reference this new class

Regards,
Matt

Yet Another Getting Things Done Timer (YAGTDT) – Two Minute Timer for GTD

March 23, 2008 By Mead Matthew Leave a Comment

There are several Getting Things Done (GTD) two minute timers available. Most are commercial, but there are a few other free products. I’d like to introduce the first open source GTD two minute timer, YAGTDT. I’m hoping the GTD community will help me make Yet Another GTD Timer (YAGTDT) the premier two minute timer available. YAGTDT is completely free and does not contain any adware/spyware. You can download the program binaries here.

Below is a screen shot of the simple and intuitive user interface:

My thoughts behind the timer and its use:

I try to implement David Allen’s Getting Things Done (GTD) as best I can. One morning I started to wonder how well I implement the GTD principles. I wondered how well I deal with everything that comes at me during the day (things come at me via email, verbally, physically in my inbox, via telephone, …) and how well I evaluate and determine if I need to do anything and if so whether it is truly actionable.

According to GTD, if I encounter something new (or have the same thought more than once) that is actionable, I must decide if I want to:

a) do it right away
b) delegate it
c) defer it

GTD further defines: If I want to do it and it takes less than two minutes, I should just do it right away. If I want to do it and it will take more than two minutes I should put the item in my GTD system and evaluate its importance and priority along with the other items I need to do. If I want to defer it, I need to put something in my system or calendar to remind me of the next action to take against this deferred item at a later date.

As I pondered about my use of GTD, I began to wonder what could really get done in two minutes? Not what could get done in approximately two minutes, but actually two minutes. And I started to think how little time two minute really is. And (yes, this is pretty sad) I wondered, for example, if setting up a meeting that requires finding people and a conference room in a corporate directory takes more than two minutes.

Well, after I experimented I found that 120 seconds is not always enough time to schedule most meetings. And, surprisingly, most emails that need to have some formality or that are more than just two lines cannot really be written, reviewed and sent in two minutes.

So this was an interesting realization and it sparked my interest in a task timer. I searched the web and found that a few timers existed, but nothing that was free and had the ability to customize the task timeout. The YAGTDT is fun to use and makes my day more interesting by challenging me to finish tasks in under 2 minutes. You simply set the timeout for a given task (2 minutes by default for GTD) and begin your task. When the task timeout expires, depending on your configuration, you will hear or chime or see a dialog stating the timeout. Because I time many tasks throughout the day, it keeps me focused (and in some sick way challenged because I’m constantly battling against time).

Personally, I would not recommend that anyone pay money for a task timer for their computer because YAGTDT is freely available to download and use (see binaries link below).

YAGTDT is very intuitive and straightforward. It defaults to a 2 minute timer. However, as Dave Allen once said in a seminar, two minutes is the GTD suggestion, but you may choose to use a 1 minutes rule or 3 minute rule. If I could do anything in 3 minutes, I’d prefer to do it right away! I don’t think 2 minutes is magic.

As a result, YAGTDT allows you to configure the timeout for a task. And, it has a few preferences that allow you to customize whether a message box pops up and whether a sound is played when the task timer expires. All of these options are available from the options link (note that this link is unavailable while the timer is counting down…you must stop the timer to change the options). Your preferences are saved and will be your new defaults every time you run YAGTDT.

From a technical development perspective YAGTDT is straightforward and therefore not too interesting. It is developed in Visual Studio 2005 using the C# programming language. It is a WinForms (Win32 Windows) application and it uses the .NET 2.0 framework. Eventually I’d like to move the project to Silverlight or WPF. I will be posting the source code for YAGTDT shortly.

System requirements: .NET 2.0 framework (download from Microsoft)

There is no installation, simple download the binaries and copy them to a location on your computer. You need to make sure you copy all 3 files (.exe is the program, .ini is the configuration file with your preferences and .wav is a sound file). If you experience any issues, you probably do not have the Microsoft .NET runtime installed. Please download it from the link above and try again to run the program, YAGTDT.EXE.

And if you encounter any problem that persists, please email me. Please leave me some feedback on the tool.

Regards,
Matt

Understanding subprojects in the NetCentrics Getting Things Done Outlook Add-In

March 13, 2008 By Mead Matthew Leave a Comment

I have to admit that I resisted using the subproject feature in the NetCentrics Getting Things Done Outlook Add-In for some time. The concept of subprojects seemed overly complicated and I didn’t see the justification to make the system any more complicated. In the GTD books I’ve read and the Dave Allen seminar I attended never mentioned subprojects…

However, just recently I encountered a multi-step project that I needed to accomplish for a non profit organization. I already had a top-level project representing my ongoing work with this organization, but this new multi-step project was quite involved and needed to be executed flawlessly. So I realized that it was time to check out subprojects and get an understanding for how they work.

I started by googling, searching the help file and looking at the NetCentrics support site, but could not find much information beyond how to create a subproject, so I resorted to figuring it out by creating one.

I created a subproject by clicking add on the subprojects tab of the project dialog. The following screenshot shows the resulting subproject on the subproject tab (click to enlarge):

After creating the subproject I was surprised that I could not interact with it. I assumed I’d be able to double click its name in the subproject list and it would open into another project window and that it would behave like any other project. I was wrong. The NetCentrics subproject is really just a description of the subset of work. It is not an entity all its own like a typical top-level NetCentrics project.

The way you use the sub project is by associating tasks to the subproject after selecting its parent (top-level) project. I had to enable the “GettingThingsDone 2” toolbar from the view menu (note that you need to be in the Task window to see this toolbar option) to see the subproject toolbar. Below are the two GTD toolbars:

GettingThingsDone Toolbar (click to enlarge):

GettingThingsDone Toolbar 2:

You can also assign tasks to a subproject when creating a task from an email:

With a subproject, I had to tweak my weekly review slightly. Instead of viewing/reviewing my projects using the “Active Tasks By Project (GTD)” view I use the “Active Tasks By SubProject (GTD)” view. This view still displays the tasks by project, but also pulls in any sub projects. Below is a snippet of the view of tasks by subproject (click to enlarge):

In summary, I plan to create more subprojects for GTD projects that are ongoing concerns. For example, my first subproject had to do with a specific project within a longer-term project (my ongoing involvement with a non-profit organization). I can see other uses for subprojects within other ongoing projects in my personal life and in my career.

Matthew Mead

Technologist and Maker

Trouble With Your Object Oriented (OO) Design? Are You Obeying the Single Responsibility Principle (SRP)?

Yet Another Getting Things Done Timer (YAGTDT) – Two Minute Timer for GTD

Understanding subprojects in the NetCentrics Getting Things Done Outlook Add-In