IBM 3270 Operator's Manual page 28

Fields and Formatted Displays
The various areas of bank checks that always contain the same type of informa-
tion are called "fields" in data-processing language, for example, the "date" field
or the "signature" field. Most documents to be entered into a host system will
be organized by fields.
This practice of standardizing the arrangement of data originated because the
person using the information could do his or her job much faster knowing that
one type of data would appear at the same location on every document.
When a display station screen is divided into fields, it makes working with the
display station quicker and easier for both the display station operator and the
host system program. The application program divides the screen into fields and
establishes the rules as to what each field will contain. The program then knows
that the same type of information will always be displayed in the same location.
Knowing this, the program can process the data from the screen much more
quickly. The operator can also perform his or her job more efficiently having
this information.
When a screen is divided into fields, it is known as a formatted screen. A screen
that the program has not divided into fields is known as an unformatted screen.
Eachjob that you work on could use a different format or none at all; therefore,
you may be working with both fonnatted and unformatted screens.
Input Fields
You may see two types of fields on your screen. One is primarily used by the
program to send you messages, instructions, and headings; you cannot key data
into this type of field. All of your entries will be into the other type. For this
reason, in the remainder of this manual, fields that you can key data into will be
referred to as input fields. Each application program user's guide should tell you
which are the input fields for that particular job.
Once a field is assigned to one type of data in a job, those character positions
should not be used for other data items in that job. For example, one field on
the screen in Figure 2-3 is called "STOCK NO". That is the only type of infor-
mation you will key into it. You will not, for instance, key the digits of an MFG
CODE number into the STOCK NO field. (Otherwise, the display station key-
board may stop functioning or a message may appear on the screen telling you
of the error.)
There is no rule stating that fields must always be a certain length or that there
will always be the same number of fields on the screen. The length of a field is
normally arrived at by determining, from the type of information that will be
entered in the field, the longest possible length of one entry. In many cases, this
is known. For example, all Stock numbers could be the same length, 9 digits;
therefore, the field for Stock numbers is 9 character spaces long. When the max-
imum length is not known, as in a field marked for customer name, maximum
length must be estimated by some method, and the field length must be set
from that estimate.
The number and names of fields that you will see on your screen will depend on
the job you are doing and the application program that is operating in the
host system.
Chapter 2 Controls and Indicators 2-13