Project Managers: Know about Conway’s Law?

From Wikipedia, available under license as detailed here: http://creativecommons.org/licenses/by-sa/3.0/:

Consider a large system S that the government wants to build. The government hires company X to build system S. Say company X has three engineering groups, E1, E2, and E3, that participate in the project. Conway’s law suggests that it is likely that the resultant system will consist of 3 major subsystems (S1, S2, S3), each built by one of the engineering groups. More importantly, the resultant interfaces between the subsystems (S1-S2, S1-S3, etc) will reflect the quality and nature of the real-world interpersonal communications between the respective engineering groups (E1-E2, E1-E3, etc).

Another example: Consider a two-person team of software engineers, A and B. Say A designs and codes a software class X. Later, the team discovers that class X needs some new features. If A adds the features, A is likely to simply expand X to include the new features. If B adds the new features, B may be afraid of breaking X, and so instead will create a new derived class X2 that inherits X’s features, and puts the new features in X2. So, in this example, the final design is a reflection of who implemented the functionality.

Law
Law

A real life example: NASA’s Mars Climate Orbiter crashed because one team used United States customary units (e.g., inches, feet and pounds) while the other used metric units for a key spacecraft operation. This information was critical to the maneuvers required to place the spacecraft in the proper Mars orbit. “People sometimes make errors,” said Dr. Edward Weiler, NASA’s Associate Administrator for Space Science. “The problem here was not the error, it was the failure of NASA’s systems engineering, and the checks and balances in our processes to detect the error. That’s why we lost the spacecraft.”

Share

The world of computers: vision 2020

vision

What would the shape of computing be 12-15 years from now? Here is where I think we will be:

My wrist watch will have my computer. When I reach office, I will place myself in front of a ‘dumb’ terminal – a monitor, a keyboard and a mouse. Embedded into the keyboard will be a smart card which will talk to my wrist watch (without cables). I will use a remote log-on software to connect to the computer inside the wrist watch – all applications will already be installed on the wrist watch and I will use them. It will also be possible to use the wrist watch as a pen drive of today. So all the data on the hard disk of this computer will be available in two ways: the remote log-on (which will also enable the use of installed applications), and USB (that is, minus the capability to use apps).

At home (and everywhere else), I will have a similar dumb terminal.

Microsoft will be dead – opensource (and portable) software like OpenOffice, and AbiWord will have caught up in terms of functionality. For profit firms of 2020 will provide support (and contribute to the enhancement to) GPL software.

Google will be going, but its offering of (office and other) applications as an online subscription (which will have become paid by then) will not be doing very well. People want to collaborate, but not at the expense of being tied down.

Electronics commerce will still have identity fraud 🙂 Sorry guys. However, the total volume digitally traded will be rising steadily.

Digital signatures would be much more easier to use, and transparent to the unitiated user. However, it will not be free from its own share of frauds.

Operating systems will be very different from today: there will be no device drivers. Every device will be plug & play, and will use universal drivers. Linux will be the defacto standard.

You have some more ideas? Please feel free to share.

Blogged with the Flock Browser
Share

When NOT to normalise the database

database
When talking of Database Normalisation, textbooks often talk of BCNF, fifth and higher normal forms. However, in practice (in large software/ERPs) I have rarely noticed normalisation beyond Third Normal form. In fact, there is a certain degree of redundancy that is desirable.

While doing database design, I believe there are two critical aspects that should be kept in mind but I see ignored in a lot of common software.

The first is the time aspect of data. First – an example from finance. Consider a company having multicurrency invoicing. The tables can be designed as:

INVOICE: InvoiceID, ..., Currency, BaseCurrency, TransactionDate, ...
CONVERSIONS: FromCurrency, ToCurrency, EffectiveDate, RateMultiplier

This is a design having no redundancy. On the basis of the three fields in the INVOICE relation, we can always find out the latest row from the CONVERSIONS table having EffectiveDate less than TransactionDate. Hence we can determine the RateMultiplier.

Consider another design:

INVOICE: InvoiceID, …, Currency, BaseCurrency, TransactionDate, RateMultiplier, …
CONVERSIONS: FromCurrency, ToCurrency, EffectiveDate, RateMultiplier

Here, the system determines the value of the RateMultiplier at the time of invoice creation and records it permanently within the INVOICE table itself. To me this would be more mature design. Why? Because a lot of data in the INVOICE table would actually depend on the RateMultiplier: for example the VAT details. If on 1-JAN-2009 we know that the exchange rate is 1.1. However, on 3-JAN-2009 we come to know that the rate was incorrectly recorded. Someone changes the CONVERSIONS table to reflect the new exchange rate, of 1.2. All the details in the INVOICE table for the invoices created between 1-JAN and 3-JAN become inconsistent since the BaseCurrency is now inconsistent with the RateMultiplier.

Now consider an example from HR appraisal systems. A table stores what stage an appraisal process is at for a particular employee. This is then used to decide what access he has.

STAGE_CURRENT: EmpID, Stage

Note that this has no Date, or Year field. An employee is trying to see records for the previous year appraisals, yet is unable to see some of the data, because current appraisal process is still in initial stage.

The next problem is that of storage of “under calculation” fields. For example, consider the training department maintains the scores of each student trained. The test administered is of 100 marks, but has a weightage 40. Proposed design:

SCORES: CandidateID, TestID, Score, Flag

At the time of recording, the Flag is set to N. Thereafter a process runs that multiplies the score by 0.4 and sets the Flag to Y.

In my opinion a better design would be to retain both the scores even though the pre-weightage score is not relevant to the business process, because a process can also terminate in between due to erroneous data being supplied. Hence if the process ends after setting the flag to Y, and before changing the score; or in reverse order: after changing the score and before setting the flag then we end up with inconsistent data. Improved design:

Scores: CandidateID, TestID, Score, WeightedScore

At the time of recording, Score is entered and WeightedScore is set to zero. Thereafter a process runs that multiplies the Score by 0.4 and stores the value in WeightedScore.

The central idea is to retain all information permanently so that even if the process fails, we know what data existed.

Share

Portable software

Portable software refers to programs that can be stored onto a media (such as USB drives, CDs, external harddisks etc.) and run directly from there on multiple computers. In other words, software that you can move from one computer to another without the need to re-install.

There are a lot of sites that provide such software for download. Google for “portable software” in general, or, say for “portable firefox” in particular. My favourite portable apps are the GIMP, and portable FileZilla (a GUI FTP tool).

Cygwin is a Linux like environment for Windows. It can run within Windows and access the filesystem. Its very useful to people like me who need Windows as the main OS, but need to test Linux shell scripts and other utilities. I even have a portable version of Cygwin, created based on these instructions. In fact, I was able to improve the procedure slightly. If someone needs help, please contact me through comments. I want to upload the ISO of the DVD created – if someone can provide the bandwidth and hosting space, I can mail a copy of the DVD to him.

Share