Placing 'sales representative' at a is wrong. Since a is a data store symbol, only a file name can go there; a person (a sales representative) is an external entity or the one who performs a process, not a data store. Also, putting 'order-receiving process' at b would make the order-receiving process the second circle in the diagram, which is inconsistent with the first circle that receives the (order request) from the customer.
×Incorrectイ
Both the order and the symbol are wrong. a is the data store written to immediately after the order-receiving process, so it is the order management file; the shipping management file corresponds to the shaded data store that comes after b (the shipping process). Furthermore, b is a circle, that is, a process, so a person such as 'warehouse staff' cannot be placed there.
○ウ
正解In a DFD, the type of symbol directly determines what kind of word can go inside it. In the diagram, a is a symbol enclosed between two horizontal parallel lines, so it is a 【data store (file)】, and b is a circle, so it is a 【process】. At this point alone, the category of word that fits each blank is already fixed. Next, follow the flow of the operations. From the leftmost 'Customer' (an external entity), an (order request) enters the first circle, which is the order-receiving process, and its result is registered in the order management file as stated in the outline of the sales management system; therefore a = order management file. The next process b, which runs by reading the data in a, is the shipping process, which allocates inventory based on the order data and carries out the shipping work; its result is registered in the shaded (not shown) shipping management file. Further to the right, the circle is the billing process, which prepares invoices from the shipped data, sends them to the customer, and registers the result in the billing management file (the shaded box at the upper right). This is consistent with the flow of the whole diagram. Hence the combination a = order management file and b = shipping process, choice ウ, is correct.
×Incorrectエ
a and b are swapped. Although a is a data store symbol, the process name 'order-receiving process' is placed there, and although b is a process symbol, the file name 'order management file' is placed there, so the correspondence between DFD symbols and elements is reversed. The words themselves are the same as in the correct answer, but they are put in the wrong positions.
ここがポイント
Distinguish the four DFD symbols: a circle = a process, a pair of horizontal parallel lines = a data store (file), a rectangle = an external entity (a customer, a business partner, and so on), and an arrow = a data flow. Just by looking at the shape of the symbol at a blank, you can narrow down in advance whether the word to fill in is a process name, a file name, or the name of a person or organization.
Reconstruct the flow by matching the description of the operations with the description of the system: the correspondences order-receiving process to order management file, shipping process to shipping management file, and billing process to billing management file, together with the order that starts with the (order request) from the customer and ends with the (invoice) sent to the customer, determine the blanks uniquely.