Category : Paradox DBMS
Archive   : TECH91.ZIP
Filename : TI783.ASC

PRODUCT : Paradox NUMBER : 783
VERSION : All
OS : DOS
DATE : September 11, 1991 PAGE : 1/3

TITLE : What in the World is a Relational Database?




A simple form of database management is called a "flat-file"
database manager. A flat-file database is a database containing
all of its information in one table. Let's assume you have a
database of customers and the orders those customers have placed.
The table you use would look something like this:

ÉÍÍÍÍÍÍÍÍÍÍÍËÍÍÍÍÍÍÍÍÍÍÍÍËÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍËÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍËÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ»
º Customer º Address º Telephone # º Part Ordered º Date of Order º
ÌÍÍÍÍÍÍÍÍÍÍÍÎÍÍÍÍÍÍÍÍÍÍÍÍÎÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÎÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÎÍÍÍÍÍÍÍÍÍÍÍÍÍÍ͹
ºJohn Doe º123 Main St.º (408)555-1212 º Backhoe º 12/25/89 º
ºBill Smith º456 Elm St. º (408)555-2424 º Vacuum Bottle º 01/04/90 º
ºJohn Doe º123 Main St.º (408)555-1212 º Jigsaw Puzzle º 02/12/90 º
ºJohn Doe º123 Main St.º (408)555-1212 º Brahmin Bull º 02/14/90 º
ºBill Smith º456 Elm St. º (408)555-2424 º Coffee Maker º 04/17/90 º
ºBill Smith º123 Main St.º (408)555-2424 º Antacid (case)º 04/18/90 º
º º º º º º
ÈÍÍÍÍÍÍÍÍÍÍÍÊÍÍÍÍÍÍÍÍÍÍÍÍÊÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÊÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÊÍÍÍÍÍÍÍÍÍÍÍÍÍÍͼ

This is certainly more efficient than trying to keep track of all
your customers on paper. If you wish, you can sort this table by
customer or by part or by date, which means you can review your
sales figures rapidly. In many flat-file databases you can
easily create reports based on your table. Flat-file databases
managers combine the virtues of power and simplicity. They are
powerful enough for many business applications, yet simple enough
that relatively inexperienced computer users can learn them in
fairly short order.

The drawback of a flat-file database is that information is often
repeated. In the table above, Bill Smith and John Doe each have
placed three orders. Instead of letting us enter their name,
address, and telephone number information once, we must enter ALL
that information again for EACH order. Not only does this mean
we have to do a lot of unnecessary work, but it introduces more
possibilities for error.





















PRODUCT : Paradox NUMBER : 783
VERSION : All
OS : DOS
DATE : September 11, 1991 PAGE : 2/3

TITLE : What in the World is a Relational Database?




A relational database, on the other hand, is designed to
circumvent these shortcomings. Relational databases are designed
to take advantage of the relationships among various groups of
data. In this case, the relationship between customers and
orders looks something like this:

ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
³ Bill Smith ³
ÀÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÙ
³ ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
ÃÄÄÄÄÄ´Vacuum Bottle ³
³ ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ
³ ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
ÃÄÄÄÄÄ´Coffee Maker ³
³ ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ
³ ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
ÀÄÄÄÄÄ´Antacid (case)³
ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

This sort of relationship is called a "one-to-many" relationship.
For every ONE customer, there are (if business is going
reasonably well) MANY orders. Now a relational database manager
(such as Borland's Paradox) knows how to capture this relation.

Instead of having ONE table in which all this information is
contained, the customer-order relation is captured in two tables,
one of which contains the master information, the other of which
contains detail information for each master record. The first
table, also called the "master" table, has all the basic customer
information:

CUSTOMER ÍÍÍËÍCustomerÍÍÍÍËAddressÍÍÍÍÍÍËÍTelephone #ÍÍÍ»
º Bill Smith º456 Elm St. º (408)555-2424 º
º John Doe º123 Main St. º (408)555-1212 º

You will notice each name appears ONCE in this table; there is no
duplication of customer records.

The second table, also called a "detail" table, contains the
order information:
















PRODUCT : Paradox NUMBER : 783
VERSION : All
OS : DOS
DATE : September 11, 1991 PAGE : 3/3

TITLE : What in the World is a Relational Database?




ORDERS ÍÍÍÍËÍCustomerÍÍÍÍÍËÍPart Ordered ÍËÍDate of OrderÍÍ»
º Bill Smith º Antacid (case)º 04/18/90 º
º Bill Smith º Coffee Maker º 04/17/90 º
º Bill Smith º Vacuum Bottle º 01/04/90 º
º John Doe º Backhoe º 12/25/89 º
º John Doe º Brahmin Bull º 02/14/90 º
º John Doe º Jigsaw Puzzle º 02/12/90 º

Here you will see that each item has a separate line. Instead of
repeating all the information for each customer, only the name
field (which is the field that "links" these two tables) is
repeated. This in itself is an advantage; we save a lot of disk
space, especially as the number of orders per customer increases.
Often the field that "links" the two tables is a code or id of
some kind versus a name; this would further save on disk space.

The quick answer is that in a database like Paradox, there is
seldom need to enter information twice. You can, with very
little effort, create "multi-table forms." Multi-table forms are
a method of combining two or more tables on one data entry form.
In Paradox, a multi-table form automatically fills in the linking
fields in the detail table. This means several things:

* Once you have entered a record in the master
table, all you have to do for new orders is enter
the new order information. This cuts down on the
work data entry people must do, and reduces the
tedium of data entry.

* The possibilities for error are reduced because
data entry work is reduced.

* All the records for any given customer can be
viewed on one screen -- without cluttering the
screen with duplicate name and address
information.

In Paradox 3.0 and up, multi-table forms are discussed in the
Paradox Presenting Data Guide.