I have been a member of many C++ and Java projects over 14
project sizes have varied including 2,3, 6, 15 and 50. I have noticed
some common problems that always seem to occur which substantially
increase the cost and reduce the reliability of the systems. These
problems are avoidable but project directors seem incapable of
effective action to manage these risks and the project planners have
inadequate flexibility in scheduling resources. Also surprising
was that the quality
was largely unrelated to project cost. When projects were
sub-contracted to a software or project management consultancy then the
policy of the 3 wise monkeys seems to dominate. Knowledge of a risk of
severe operational difficulties for the end-client would not be
communicated to the client.
An object-oriented approach moves much of the software development effort up to the analysis phase of the lifecycle It is sometimes disconcerting to spend more time during analysis and design, but this extra effort is more than compensated by the faster and simpler implementation. Object Oriented Modelling and Design / James Rumbaugh et al. 1991 p 146
A larger fraction [50%] is spent on the design phase; a comparably smaller fraction [30%] of the overall time is spent on implementation and testing. Designing Object Oriented Software / Rebecca Wirfs-Brock et al. 1990 p 8
Many programmers, when presented with a clear error-free design, are capable of extraordinary rates of code production. It is my experience that many of the project problems would have been resolved by spending more time on analysis and design.
A defect introduced during requirements specification will cost 100-1000 times more to correct when the system is in the testing phase than it would cost to fix during requirements specification. Object Oriented Software Engineering / Ivar Jacobson et al. 1992 p 467
It is my experience that the requirements specification contains
errors and omissions. The errors could have been reduced by the use
of analysis according to Jacobsons OOSE method or Rational's RUP
process. I also found that
since the requirements were written by senior staff, they were not
subject to critical review by other suitably skilled persons.
Non-functional and operational requirements need more design attention
than is usually given.
Programmers are versatile and are paid by the hour (or up to £1250 per day for a sub-contracting company), so all the errors and difficulties are worked around at extra cost for the client.
A very common mistake is a failure for the designers/programmers
to recognise when it is appropriate to use the design patterns as
detailed in the book Design Patterns. Most large
projects should use almost all of these patterns. The essence of most
design patterns is the separation out of aspects of an object that
are likely to change or be customised.
Domain specific modelling is not usually performed in enough detail.
More time should be spent with the domain experts teasing out the
inheritance, relationships and behaviours of domain specific objects
Implementation reuse by means of inheritance and delegation was not used enough. Instead the source code was copied and then edited. I have seen up to 7 classes of FileDialog created using the cut and paste technique. The use of Jacobsons modelling technique of distinguishing Interface, Control, and Entity objects would help to permit greater implementation re-use.
Compile and Link dependencies between source modules can quickly become unmanageable. In some small projects this results in requiring a complete recompile and relink of all the source to get a usable executable. In the extremely large projects, it may take a week just to get one clean integration build. It helps to use design patterns to separate interface from implementation and also to allow a single object to present several smaller interfaces.
Inter-object "ownership" and "references" relations quickly become confused. The result is that the responsibility for deletion of an object is not implemented and the executable process leaks memory. When you try to start deleting objects, you sometimes find that it is not possible to determine what other objects still reference it; then you get crashes. Memory management is such a chore in C++ that much of the time you should not use dumb pointers. (Use smart pointers or Java (Why Java?)). It becomes almost impossible to manage memory when all the exception and error code paths have to be considered.
There is often a performance problem that only becomes visible when collection sizes grow. These are not difficult to find and fix provided that the testing specifically takes collection size factors into account. I have found that the system architect or the designer should check for potential architectural speed limitations and also prototypes of the most important use-cases should be instrumented and timed to characterise the delays and throughputs. The programmer should not usually attempt to optimise before it has been shown to be necessary by the testers. Optimisation is a prime cause of error. A revised design may produce larger gains than merely altered code. If optimisation is ever performed by the programmer, the non-optimised version should also be available switched at run-time or compile time. Screen redraw time is often a limiting performance factor. It can be improved by using incremental asynchronous update techniques, but multi-threading and object dependency tracking is an issue which must have been considered at design time.
Most programs require that 2 or more activities occur concurrently. It is essential that issues of dependency between objects and resource locks are fully considered at the design stage. All projects that I have worked on suffered from update/locking problems at a late stage.
All projects that I have worked on said that they would perform
reviews. In practice, review is just not done until it is too late to
avoid disaster. Review the design before you write the code. Re-review
everything, including concept of operations, requirements, tools,
processes. An error or ommision is still an error even if discovered
after signoff or after a phase has been nominally been finished.
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