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218 Part 3 • the analysis Process

c. A table of codes is suitable if the list of values is extensive (for example, state abbrevia-
tions, telephone country codes, or U.S. telephone area codes.)
d. For key or index elements, a check digit is often included.
10. Any default value the element may have. The default value is displayed on entry screens
and is used to reduce the amount of keying that the operator may have to do. Usually,
several fields in each system have default values. When using GUI lists or drop-down
lists, the default value is the one currently selected and highlighted. When using radio
buttons, the option for the default value is selected, and when using check boxes, the
default value (either “yes” or “no”) determines whether the check box will have an ini-
tial check in it.
11. An additional comment or remarks area. This might be used to indicate the format of the
date, special validation that is required, the check digit method used (explained in Chapter
15), and so on.
Data element descriptions such as CUSTOMER NUMBER may be called CLIENT NUMBER
elsewhere in the system (and perhaps old code written with this alias needs to be updated).
Another kind of data element is an alphabetic element. At World’s Trend Catalog Division,
codes are used to describe colors—for example, BL for blue, WH for white, and GR for green.
When this element is implemented, a table will be needed for users to look up the meanings of
these codes. (Coding is discussed further in Chapter 15.)

Data Stores
All base elements must be stored in the system. Derived elements, such as the employee year-to-
date gross pay, may also be stored in the system. Data stores are created for each different data
entity being stored. That is, when data flow base elements are grouped together to form a struc-
tural record, a data store is created for each unique structural record.
Because a given data flow may only show part of the collective data that a structural record
contains, you may have to examine many different data flow structures to arrive at a complete
data store description.
Figure 8.9 is a typical form used to describe a data store. The information included on the
form is as follows:
1. The data store ID. The ID is often a mandatory entry to prevent the analyst from storing
redundant information. An example would be D1 for the CUSTOMER MASTER.
2. The data store name, which is descriptive and unique.
3. An alias for the table, such as CLIENT MASTER for the CUSTOMER MASTER.
4. A short description of the data store.
5. The file type, either computer or manual.
6. The format designates whether the file is a database table or whether it has the format of a
simple flat file. (File formats are detailed in Chapter 13.)
7. The maximum and average number of records on the file as well as the growth per year.
This information helps the analyst to predict the amount of disk space required for the
application and is necessary for hardware acquisition planning.
8. The file or data set name specifies the file name, if known. In the initial design stages, this
item may be left blank. An electronic form produced using Visible Analyst is shown in
Figure 8.10. This example shows that the CUSTOMER MASTER is stored on a computer
in the form of a database with a maximum number of 45,000 records. (Records and the
keys used to sort the database are explained in Chapter 13.)
9. The data structure should use a name found in the data dictionary, providing a link to the
elements for this data store. Alternatively, the data elements could be described on the data
store description form or on the CASE tool screen for the data store. Primary and second-
ary keys must be elements (or a combination of elements) found in the data structure. In
the example, the CUSTOMER NUMBER is the primary key and should be unique. The
CUSTOMER NAME, ZIP, and YEAR-TO-DATE AMOUNT PURCHASED are second-
ary keys used to control record sequencing on reports and to locate records directly. (Keys
are discussed in Chapter 13.) Comments are used for information that does not fit into
any of the above categories. They may include update or backup timing, security, or other
considerations.