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202 Part 3 • the analysis Process

processes and unique partitions in making a flight reservation. Process 1 receives and validates
the dates and airports entered by the customer (or travel agent acting for a customer). The selec-
tion data is used to obtain flight details and create a transaction data store of flight details that
match the flight request.
It is advisable to partition the process of finding the flight information as a separate pro-
cess because a data store must be searched, and the flight details are used to display a series
of successive web pages with matching flights. Then, once a customer chooses a flight, the
information must be sent to a selected airline. It is important to have the FLIGHT DETAILS
transaction file available to display each web page of new flights because redoing the search
may take a large amount of time that is unacceptable to a human user trying to complete a
transaction.
The selection of available flights (process 2) uses an internal database, but this database
does not have information about availability of seats, because the airlines are receiving res-
ervations from many travel service organizations. This means that there must be a separate
process and small program partitioned for determining if seats are available and for reserving
specific seats.
Because there is a lot of user input, forms are designed to handle all the user requests.
Having separate forms means that the forms are less complex, and therefore users will find them
more attractive and easier to fill out. This design meets both the usability and usefulness criteria
important when designing websites for human–computer interaction. It also means that process-
ing will take place more quickly because once the flight is chosen, the next step involving the
choice of seats should not require the customer to input or even see the flight details again at
this time. Most airline websites now use pop-up windows in which customers point to their seat
selection.
Another reason for partitioning is to keep the transaction secure. Once the seat has been
selected, the customer must confirm the reservation and supply credit card information. This is
done using a secure connection, and the credit card company is involved in validating the amount
of purchase. The secure connection means a separate process must be used. Once the credit card
has been confirmed, two additional processes must be included, one to format and send an email
confirmation and an e-ticket to the customer and another to send notification of the flight pur-
chase to the airline.
The entire procedure must be partitioned into a series of interacting processes, each with
a corresponding web page or interaction with an external system. Each time a new data store
is used to obtain additional data, a process must be included to format or obtain the data. Each
time an external company or system is involved, a process needs to be partitioned into a separate
program. When processes or forms need to be revised, it is not a major task. The small size of
the programs makes them easy to change. In this way, the website is secure, efficient, and more
easily maintained.

Communicating Using Data Flow Diagrams
Data flow diagrams are useful throughout the analysis and design process. You use original,
unexploded data flow diagrams early when ascertaining information requirements. At this stage,
they can help provide an overview of data movement through the system, lending a visual per-
spective unavailable in narrative data.
A systems analyst might be quite competent at sketching through the logic of the data
stream for data flow diagrams, but to make the diagrams truly communicative to users and other
members of the project team, meaningful labels for all data components are also required. Labels
should not be generic because then they do not tell enough about the situation at hand. All gen-
eral systems models bear the configuration of input, process, and output, so labels for a data flow
diagram need to be more specific than that.
Finally, remember that data flow diagrams are used to document the system. Assume that
data flow diagrams will be around longer than the people who drew them, which is, of course,
always true if an external consultant is drawing them. Data flow diagrams can be used for docu-
menting high or low levels of analysis and helping to substantiate the logic underlying the data
flows of the organizations.