How would you accomplish this task?
First ,you would probably go through the customer files in alphabetical order, foler by folder.
You would examine each invoice in the folders to determine if the amount is in excess of $2,500 and remove and copy each invoice that meets the criterion.
You would then have to refill the copies you removed and risk misfiling them
When you had examined all the customer folders and copied all the appropriate invoices.
you would then review the copies and put together your report.
Imagine how much time this would take.
If there are a lot of customers, you would need to spend hours if not days.
Now let's look at the situation in a different way.
The environment is the same , except that ,instead of file cabinets.
you have a microcomputer or a terminal and DBMS software that has access to a customer database file as shown in the following .
In this file a row of customer data is referred to as a record, and an individual piece of data within a record ,such as a name ,is referred to as a field.
To get the invoice data you need, you would do something like this.
Turn on the computer and the printer.
start up the DBMS software
Give the command to open up the customer database file stored on your disk ,which is similar in concept to manually opening up the customer file in a filing cabinet.
Give the command to search all the records in the database file and display copies of the records that meet your criterion.
that is the names of people with unpaid invoices greater than $2,500.
If you were using dBASE IV , a popular microcomputer DBMS ,the command would look something like.
If you were using SQL( Structured Query Language) the command would look like this.
In response to this command ,all the records in the file that have an invoice amount greater than $2,500 will be listed on the screen.
The SQL command would also sort the listing into order by name.
This whole procedure would take perhaps only five minutes or less.