Feeds

Sequence diagramming that's fit for purpose

Illustrate your point

Designing a Defense for Mobile Applications

Sequence diagramming in practice - test yourself

Continuing with our sample internet bookstore application, the following diagram shows an excerpt from a sequence diagram for the "Create New Book" use case. This use case is intended for bookstore staff, so that they can add new book titles to their online catalog. There are a couple of problems with this diagram excerpt - one of which is repeated many times in our diagram. See if you can find them both. Hint: the errors relate back to items one and seven in the top-10 list.

Iconix Process sequence diagram exercise one

Hidden problems: flawed sequence diagram

Our next illustration highlights the parts of the sequence diagram that have gone wrong. The main issue is that the sequence diagram is being used as a flowchart, instead of for its primary purpose in life: to allocate behavior to classes.

Flowcharting on sequence diagrams isn't necessarily an evil thing in and of itself, and it is almost certainly better than not doing the sequence diagram at all. But we consider it to be (at best) a weak usage of a sequence diagram because it doesn't leverage the ability to assign operations to classes while drawing message arrows.

Since, in our opinion, this activity is pretty much the fundamental place where "real" object oriented design happens, we've flagged it as an error.

The second issue is that there’s no validation performed on the incoming form data - and therefore no error handling code for rejecting bad data. Either the validation steps were left out of the use case or the designer didn't draw the sequence diagram directly from the use case text.

Iconix Process sequence diagram exercise two

Problems exposed in the sequence diagram

Boost IT visibility and business value

More from The Register

next story
Chrome browser has been DRAINING PC batteries for YEARS
Google is only now fixing ancient, energy-sapping bug
HIDDEN packet sniffer spy tech in MILLIONS of iPhones, iPads – expert
Don't panic though – Apple's backdoor is not wide open to all, guru tells us
Do YOU work at Microsoft? Um. Are you SURE about that?
Nokia and marketing types first to get the bullet, says report
Microsoft takes on Chromebook with low-cost Windows laptops
Redmond's chief salesman: We're taking 'hard' decisions
Cheer up, Nokia fans. It can start making mobes again in 18 months
The real winner of the Nokia sale is *drumroll* ... Nokia
EU dons gloves, pokes Google's deals with Android mobe makers
El Reg cops a squint at investigatory letters
Big Blue Apple: IBM to sell iPads, iPhones to enterprises
iOS/2 gear loaded with apps for big biz ... uh oh BlackBerry
prev story

Whitepapers

Reducing security risks from open source software
Follow a few strategies and your organization can gain the full benefits of open source and the cloud without compromising the security of your applications.
Consolidation: The Foundation for IT Business Transformation
In this whitepaper learn how effective consolidation of IT and business resources can enable multiple, meaningful business benefits.
Application security programs and practises
Follow a few strategies and your organization can gain the full benefits of open source and the cloud without compromising the security of your applications.
Boost IT visibility and business value
How building a great service catalog relieves pressure points and demonstrates the value of IT service management.
Consolidation: the foundation for IT and business transformation
In this whitepaper learn how effective consolidation of IT and business resources can enable multiple, meaningful business benefits.