Amiga Computing - Commodore Is Awesome

84
SOFTWARE
ou know, I've tried a few database
programs in my time, but very few of
them ever seem to attain that fine
line balance between ease of use and power.
Mostly you have one end of the scale tipped
to one side at the detriment of the other To
easy to use and they often seem to lack any
real power. Too powerful and they become
overly cryptic with masses of commands and
features hidden away within an ominously
imposing and large manual, that has a page
count that would make the encyclopaedia
Brittanica blush.
Yes, there are very few which can claim to
maintain their footing between these two
extremes. Twist 2, from the ever prolific
HiSoft, is one of them, however.
Versatility is one of Twist 2's strengths.
allowing you to organise information easily
and quickly and to manipulate it using some
extremely powerful functions and features.
Any project from a simple card-file-type
address book or a complete, integrated sales
system with relations between many other
database files are easily achieved using
Twist 2_
Creating and using a database generally
consists of creating fields containing specific
data which is collected into records and then
organised into forms. The user can then
access, search and generally process this
organised data in many weird and wonderful
ways using various functions and features
built into the database.
A quick scan of the reference section of
the Twist 2 manual is evidence enough to
realise you have a comprehensive and powerful
suite of functions and features at your
ingertips_ Thanks to the ARexx interface.
those requiring even more power can turn
their hand to this programming tool to create
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Presentation of your data is an important factor in how easy to
read and informative your records look. Twist 2 allows you to easily
create the look of your database via the Form editor. Using the
mouse, simply click and drag the various form objects into
position. sizing them to your requirements.
These form objects include database Fields, Text for adding
informative descriptions on the form. Box. which allows you to provide
a visual indication of grouped Items. Image, to enable you to
display icons on the form and, more Interestingly. File objects.
File objects are quite a powerful feature within Twist 2 and allow
you to use external files thanks to Workbench's Datatypes feature.
Such external files can Include !FT' pictures, sound samples and
any other filetype supported by the Datatype.
Some of these form objects can also have attributes such as
colour, allowing you to create a visually informative and even
aesthetically-pleasing database.
Amiga Computing
MAY 1995
twi5t and
Using tha report aditor, you can da•ign the way
in which your data i• formatted in a report Me
even more features and functions. The basic
building block of a database is its fields,
which are specific data elements of a
specific data type. Twist 2 has four main
types of data which are text, numbers
(integer or floating point) or a calendar date.
The mark of a quality database program is
In what functions and processes can be
applied to these fields. Twist 2's real power
stems from its comprehensive array of functions
which include statistical, boolean, geometric,
text string and conditional functions -
more than enough for most applications.
CALCULATIONS
You can assign a mathematical process to
fields to automatically calculate figures_ For
example, say your database has a floating
point field called Value which holds the price
of a certain product excluding VAT.
However, you want to be able to include
VAT should the need arise_ Therefore, you
assign a field called VAT to be a floating
point number which can either hold the number
0, for no VAT or 17.5 for the current rate.
You would thus edit the Value field to contain
the expression (Total • (VAT 100)) +
Total, which will give the full price including
any VAT if present. Although a somewhat
simple example. the range of functions and
possible expressions is almost unlimited_
Other field functions that can be applied
include validation, which ensures the correct
data is being entered. An example of this
would be the VAT field. Obviously, the only
values valid here are either 0 or 17.5.
To ensure the operator cannot enter any
incorrect figures, this field could be validated
using the expression VAT =-0 II VAT
=17.5_ In English, this expression is essentially
saying that the VAT field can only have
the number 0 OR (expressed as the II
characters) 17.5 in it, and anything else is
just not on!
Thankfully, for those who are currently
scratching their heads at the above expression,
there is a complete reference section in
the Twist 2 manual which describes aN toe
various symbols and mathematical opera
tors. If, after reading this, I can get the gist cd
it, anybody can.
There are also five attributes which Team
2 can assign to a field. These are Not
edrtable (pretty self explanatory), Required -
which means the field must have data
entered into it, Fixed - meaning once data
has been entered, no further calculation at
validation will be performed - Zero -
empty. forces a field to a zero value if no
data is present - and the last attribute. Fille_
brings up a pop-up list which displays three
settings. Fixed length. Compressed and
Virtual, These are very useful when your
database starts to attain mammoth
proportions.
When you save your database, every field
and record is saved to disk. The default setting
is Fixed length. which means all parts cd
every record in the database, whether al
characters are used or not, are saved to
disk. If you have quite large text fields, the
size of the database can rapidly become
extreme, taking up copious amounts of
valuable disk space.
This problem can be avoided by the use
of the Compressed option. If a field is set to
compressed it is not stored in the main database
file but in a second file which contains
all the other compressed fields that happen
to be present within the database. The
obvious drawback, of course, is that the
information takes a little longer to retrieve
because Twist 2 can't immediately find it in
the database file.
The final setting is Virtual, and no, Twist 2
doesn't come with a VR headset. The Virtual
setting stores nothing at all in the database
file; instead the content of the field is computed
every time the record is used from the
calculation attached to the field.
Fields can also be Indexed, which means
all values for a field are contained in a separate
file and can be set to either ascending
Anital
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