Author Archives: Glennan Carnie

About Glennan Carnie

Glennan is an embedded systems and software engineer with over 20 years experience, mostly in high-integrity systems for the defence and aerospace industry.

He specialises in C++, UML, software modelling, Systems Engineering and process development.

Revision Control

What is Revision Control?

Revision control is the management of multiple revisions of the same unit of information. The focus is on controlling access to the artefact; and recording the history of changes.

Revision Control is variously known as version control, source control, source code management and several other titles.

Revision control has its roots in the management of engineering blueprints and paper documents. Today, any practical application of Revision Control requires the use of specialist software tools.

Artefact Identification

The core to revision control […]

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What is Configuration Management? And why is it important to me?

What is Configuration Management?

Configuration Management has its roots in the US Department of Defence in the 1950’s. It started as a technical management discipline and has been widely adopted by many other engineering disciplines, including Systems Engineering and Software Engineering. Configuration Management focuses on establishing, and maintaining, the consistency of a system or product throughout its lifetime. CM is a collection of competencies, techniques and tools whose purpose is to ensure the consistency of the system’s requirements, functional attributes and […]

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Fundamentals of Configuration Management

Configuration Management (CM) is a core process in any development activity. Software engineers realise this more than any other discipline, but for many software teams using Subversion as a source code repository is as far as they get. Configuration Management is a lot more than this.

These articles introduce the fundamental concepts of Configuration Management and what they mean to the development team. Revision control is the most well known and understood CM activity but few extend this to develop artefact […]

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GNU, and void pointers

Void pointers were introduced in ANSI C as ‘generic’ pointers; or, if you prefer, ‘pointers to no particular type’. They were designed to replace unsigned char* pointers in instances where the type of the object being pointed to could change.

unsigned char* has the least restrictive alignment – it aligns on a byte boundary. This means an unsigned char* pointer could be used to point to any object (with an appropriate cast, of course).

Remember, though, the type of a pointer defines […]

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Inheritance, ABCs and Polymorphism

Virtual functions

Virtual functions in C++ exist to maintain the consistent behaviour of polymorphism when accessing derived objects via base class pointers. (If that statement has made your head spin, I’d suggest reading this article before carrying on)

class Base
{
public:
virtual void v_op();
};

class Derived : public Base
{
public:
virtual void v_op();
}

I can access either a Base object or a Derived object via a Base pointer; and I should get the appropriate behaviour for the actual type of the object I’m pointed at:

Base* […]

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The Baker’s Dozen of Use Cases

Use cases have become a core part of the requirements analyst’s arsenal.  Used well they can bring dramatic increases in customer satisfaction and a whole host of other subtle benefits to software development.

The use case itself is very simple in concept: describe the functionality of the system in terms of interactions between the system and its external interactors.  The focus of the use case is system usage,  from an external perspective.

Despite this apparent simplicity, requirements analysts frequently struggle to write […]

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The Baker’s Dozen of Use Cases

Rule 13: Say it with more than words

Use case descriptions are most commonly written in text format (albeit often a stylised, semi-formal style of writing). Text is a very effective method of describing the transactional behaviour of use cases – it’s readily understandable without special training; most engineers can produce it (although the ability to write basic prose does seem beyond the capability of many!); and it is flexible enough to deal with complex behaviours – for example, variable numbers […]

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The Baker’s Dozen of Use Cases

Rule 12: Avoid variations on a theme

A common affliction amongst novice use case modellers (particularly those from a development background) is the desire to fettle the use case model – to organise it, revise it, balance it; and generally make it look more like a design model.  Unfortunately, beyond a certain point this effort actually starts to degrade the utility and effectiveness of the model.  More and more effort is put into a model that becomes less and less useful […]

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The Baker’s Dozen of Use Cases

Rule 11 – Don’t abuse «include»

A use case contains all the steps (transactions) needed to describe how the actor (our stakeholder) achieves their goal (or doesn’t; depending on the particular conditions of the scenario). Therefore a use case is a stand-alone entity – it encapsulates all the behaviour necessary to describe all the possible scenarios connected to achieving a particular end result. That’s what makes use cases such a powerful analysis tool – they give the system’s requirements context.  Use […]

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The Baker’s Dozen of Use Cases

Rule 10:  The magical number seven (plus or minus two)

Psychologist George Miller, in his seminal 1956 paper "The Magical Number Seven, Plus or Minus Two: Some Limits on Our Capacity for Processing Information", identified a limit on the capacity of human working memory. He found that adults have the capability to hold between five and nine ‘chunks’ of information at any one time. A ‘chunk’ may be a number, letter, word or some other cohesive set of data.

What has this […]

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