The next question that you, as a developer, need to consider is where the data from the application is coming from and where it will be stored. This application is particularly complex because there will be data coming from outside sources (stock quotes), data entered by the user (transactions and account information), and data entered by the staff (news stories). Because historical as well as current stock information will be needed (eventually, for example, it would be good to be able to display charts of stock prices over time), the stock quotes will be stored in the database and updated hourly. In the finished application, a separate program would run, getting the quotes and writing them into the database. For this example, the quotes will be made up randomly and stored for future use. A quick pass over the requirements can pull out all the objects that will be needed to make the application run:
This object list can be turned into an entity relation diagram (ERD), as shown in Figure 6.7. Figure 6.7. The ERD for the Stock Tracker application.
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