Software Engineering

10.2.3 
Data item
Data items represent information that must be processed by the software prod-
uct. Data items may be complex in nature and may need to be decomposed to 
express the specific data elements involved with the data processing. For exam-
ple, a debit card is encoded with account information that is read by an automated 
teller machine’s (ATM) card reader. The initial data item may be generalized as 
“account information.” However, it is important to be precise in expressing the vari-
ous pieces of information encoded on the debit card. Typical customer information 
may include customer name, card expiration date, bank routing number, checking 
account number, and savings account number. Each of these information elements 
must be identified as a data item at some level of the functional decomposition to 
express the data specification.
Data items involve characteristics that may affect the performance of the soft-
ware product. Data has a size attribute expressing the amount of information repre-
sented by the data item, which may affect storage, retrieval, and transmission rates. 
Transmission rates affect the time it takes to transfer a data item between functions, 
which is constrained by the computing environment’s internal bus subsystem that 
transfers data between components inside a computer or between computers via an 
external interface. The capacity of an external interface also affects the transmission 
rate of data from the host computing device to external systems.