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DATABASE.TUT
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████████████████████████████████████████████████████████████████
USING DATABASES - THAT FEELING OF POWER
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It is said that there are three classes of programs which
interest business and home computer users:
Word processors help you talk about money. Spreadsheets help you
keep track of money. But databases help you MAKE money. Given
that provocative insight, let's probe deeper . . .
A database program allows you to store, sort, organize, retrieve
and prepare reports about information in a logical way. Facts,
figures and ideas all benefit from careful organization,
retrieval, sorting and storage. Spreadsheets come with a formal
layout (rows and columns) and are best used for examining
relations BETWEEN items and MANIPULATING the results.
Databases require a more STRUCTURED format for the information.
They are, however, more flexible in layout and allow more
reporting variety on the information contained in the database.
Most databases work with records or forms (like 3 x 5 cards).
You can specify the information contained: names, addresses,
client types and so on. Each form within a database always
contains the same information. Just like filing cards which
always contain the same entries. A good way to think of a
database is a shoebox with many baseball cards - each with the
same headings (field names). Each card of course contains
different information. An important term used in describing and
working with databases is the FILE which is a collection of
similar RECORDS like a shoebox full of baseball cards. A RECORD
is the data items which are duplicated to make up the file (each
baseball card.) Each record has FIELDS which are items within
like the date of birth for an individual baseball player. Lower
still is the CHARACTER is simply an individual number, symbol or
alphabet letter. Characters are sometimes called character
strings. Common character data might include names, product
labels, numeric identification or other data. In addition some
fields are fixed in length and must be set prior to database use
(e.g., PC FILE:DB) while others allow flexible length character
strings to be entered (e.g., Microsoft Works). These limits are
set by either or both the available disk space and available RAM
memory space.
But many databases extend still further. New database products
include capabilities for graphing relationships between sets of
data, producing summaries and even working with pictures.
Another useful feature is error checking within a database which
means that if the field is preset to only allow zip codes, if a
dollar amount or state abbreviation is mistakenly entered, the
computer will beep and pause for another try. Further databases
can be preset to only work in some fields with real numbers or
integers depending on data needs.
An example database screen:
=================================================
---- CUSTOMER LIST ----
name: product used:
address: frequency of use:
city: social security no:
state: birthday:
zip: category:
remarks: date of first contact:
=================================================
The above is a simple screen layout for a database customer file
or christmas card mailing list. Many databases can also list
information in columns or a list view) and in many different
report styles. The exciting idea behind databases is that you
can retrieve a single record or groups of records very quickly.
You could, for example, locate all customers who use a
particular product. Or perhaps all customers in the same city
over a certain age (calculated from the birthday field) who
purchased from your store within the last year.
There are two general styles or types of database programs:
single file (also called flat file or file manager type) and
multi-file (also called relational). Single file type databases
operate on one set of information at a time while multi-file
(relational) databases work with many interrelated sets of data
at once. An example of single file would be cards in a recipe
box; the cards could be sorted, searched and checked one at a
time. A relational, multi-file database could interrelate a set
of recipe cards to a set of cooks and a set of diners and a set
of dates available for dinner - all at the same time! Complex,
but useful . . .
Generally, single file databases are easy and relatively
inexpensive (as well as being suitable for beginners). Examples:
Microsoft Works, Pc-file, Q & A and Reflex. Multi-file
databases are more complex, and more expensive. Examples: dBase,
Paradox and Rbase.
Some databases store excess data during program operation on
disk, while others store data only in limited RAM memory during
operation and then place data on disk when the computer is shut
off. Disk based databases can hold more information but are a
little slower searching and sorting. RAM based databases are
fast but can only hold a finite amount of data since they must
contain everything within RAM. Generally many relational
databases are disk based while flat file, simple databases are
RAM memory based.
Reporting capabilities are also of interest. A database must be
able to "let you see" or REPORT the data in different ways. Some
format possibilities are columns, cross tabs, graphs and
extracted lists. The idea is flexibility in printing of reports.
The sorting of data is crucial. A sort refers to the reordering
of data on the disk or within RAM memory. You might wish to sort
your database into a list by zip code order to take advantage of
bulk mailing rates. Later you might wish to resort the same data
into a list with high income customers are the top and low
income customers at the bottom. The useful possibilities are
endless. Disk based database programs usually store a special
INDEX file which cross references the main data and keeps track
of where individual records are located. This allows for faster
searching and sorting since the smaller index is examined rather
than churning through all the records to find or delete data.
Multiple indexes refers to the capability to have separate
indexes on one database. Each index reflects a different sorting
pattern.
Searching or selecting data can be tedious or easy depending on
the program. Some programs like Q & A allow you to recall data
by asking in simple english sentences or phrases. This may be
easy at first but limits greater intricacy later. Most programs
allow for expressions which can search at a refined level but
require phrases such as:
STATE="WA" or STATE="OR" and INCOME >="$45,000"
This is a bit more "mathematical" in appearance but isn't hard
for the beginner to master with practice. This more
"mathematical" approach to searching allows pinpoint accuracy.
Modern database programs can act a bit like spreadsheets in
allowing the calculation of fields. This means that if a number
or item is entered into a field of the database, another field
will instantly "fill itself in" with a number or word
automatically. This calculation of results is based on the entry
of the previous field! Many databases have built in functions
just like spreadsheets. You can use them to calculate loan
amounts, quarters within the calendar year, cosines, and other
results based on a previous field of data.
Databases can operate in one (or several) of three distinct
ways: 1) Menus are present which you pull down to select choices
such as sorting or deleting data. 2) Macros are invoked which
simply play back pre-recorded sequences of typed commands. For
example you press the key combination ALT-S and a special macro
you pre-recorded earlier issues a series of commands to the
keyboard which tell it to retrieve a certain file, search it for
high income customers, sort the data into order by zip code and
then print a report list. All this from one keystroke! 3) The
final method for database operation is full programming mode
which allows the package to perform under the control of a
sophisticated series of commands which accept data, sort and
search it and make decisions as to which part of the program
should be used next. A programmed database is useful when full
sophistication is needed or when untrained workers must not be
allowed to tinker with the underlying database. Programming
controls the steps the database uses to perform its job.
Increasingly, external vendors provide written programs which
can, for example, allow a package such as dBase to function as
an accounting package for a pharmacy or a fund raising database
for a church. The program changes the structure and performance
of the database to a precisely tuned information system for a
specific need.
Yet another area of interest is the importing and exporting
(transfer) of data between database programs. Some computer
users maintain data and report on results from a database
program. However the data can be transferred from the database
to a spreadsheet for closer analysis, graphing or consolidation.
This transfer capability also allows you to "take your data" to
another database program if you outgrow the capabilities of a
simple database package which becomes limited in capabilities
and must be discarded. You may have to discard the program, but
need to take the data from it into a newer database program.