Database design course
Modern graphical tools make it easy for a novice who knows nothing
of the principles of database design to create a simple database.
These tools are invaluable but the danger is that they concentrate
on the appearance of the database forms and reports on screen,
rather than on the way that the data should be stored and
structured in an efficient relational database.
This visual approach allows a user to produce a good-looking
program very quickly. The interface will look as thouigh it works
and the database will accept and display its first few dozen
entries. It might work well for many months but as the volume of
data grows drawbacks in the underlying structure will begin to
appear. Users can face problems of performance and integrity and
expansion will be very difficult.
Performance
All databases run more slowly as they grow larger but the effect will
be minimal in a well-designed system.
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An average design will slow down in step with the growth in
the volume of data being stored. It will halve in speed when
the size doubles and will fall to a tenth of its original
speed with ten times as much data.
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A good design will slow less drastically.
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A bad design might slow with the square of the size - falling to a
hundredth of the speed with ten times the data. It is very common
to meet a database like this which worked well under test conditions
with a few dozen records but which has slowed to a crawl in
production use where it might have tens of thousands of records.
Different types of database need different designs. Some must be
optimised for speed of manual data entry, others import their data
electronically from on-line sources but must be organised so that
regular reports can be produced quickly easily. The most sensitive
application is one where the user is working with the database as
they are speaking to a customer. It may be commonplace to hear
"I'm sorry but the database is very slow." but that excuse does
nothing for customer confidence.
Integrity
All data being held must be accurate if it is to be of any use to the
business. A bad design will rely on the user copying entries from one
place to another and mistakes are inevitable.
Inconsistent data is the very worst failing that a database can suffer from. If
an item of data is completely and consistently wrong then a user can
apologise to the customer or manager for the mistake, put the data right
and be confident that they have fixed the problem. When a database holds
inconsistent data then users begin to mistrust it. They find that a name
has been spelt wrongly and put it right but then they find that the name
is still coming out wrong because the database holds duplicate and
inconsistent values. Users (and customers) quickly lose confidence in a
database when this happens. Examples appear regularly in the press.
Expansion
As well as growing larger in size, databases also grow as users request
more features. A well-designed relational database will allow for this
growth.
This short course addresses these three issues and will help you to create
databases that will be robust and reliable and able to grow.
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"Geoff Franklin proved to be very responsive to my request for urgent help with Access database information. He took me from a standing start to producing simple reports in 1 day and solved a long outstanding problem with extracting Foxpro based tables , which our reseller had failed to complete. At the end of the day we had a short usable outstanding Purchase Orders report - a first in 10 years! Highly recommended."
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