Assignment

"The JavaScript Math object contains advanced mathematical methods and constants. ... Using some of the Math object methods, create a calculator that performs advanced calculations, including the exp() (exponential value) function and the sqrt() (square root function). Instead of using the eval() method to evaluate the contents of a text field, allow users to type a number into a text field and then calculate the number directly using individual buttons for such advanced math functions. Save the program as AdvancedCalculator.html." (p. 169 of book)

In her day job, Elizabeth works as the human factors engineer on a system engineering team that defines requirements for enhancements to an information system, and provides them to the software engineering team for implementation. The clearest way to state what a product must do — so that it can be designed, coded, and tested unambiguously — is to write the "shall" statements that the assignment contains. (It is also the best way to make sure the assignment is understood and to identify any questions about it.)

These requirements (also called "shall"s) consist of two kinds:

• Explicit requirements are specifically contained in the assignment or the specification of what the product must do
• Derived, or implicit, requirements are identified and defined (usually by the software team) to capture what is implied but not specifically stated by the explicit requirirements.

This assignment has four explicit requirements, and yields four derived requirements.

Requirements

Explicit requirements:

1. The Advanced Calculator shall perform built-in JavaScript functions, including but not limited to the EXP and SQRT functions.
2. The Advanced Calculator shall accept input typed from the keyboard into a text field.
3. Each of the advanced math functions in the Advanced Calculator shall use a button that operates directly on the number in the text field.
4. The Advanced Calculator shall be stored in a file named AdvancedCalculator.html.

Derived requirements:

1. The Advanced Calculator shall replace the number in the text field with the result of the calculation. (reason: It has to go somewhere.)
2. The Advanced Calculator shall limit its advanced math functions to those that accept only one text input from the user. (reason: There's only one text input field.)
3. The Advanced Calculator shall leave the result in the text field until the user enters a new one. (reason:
4. The Advanced Calculator shall provide a "Clear" button that erases the current contents of the field. (reason: The user has to have a way to start over.)

These last four are really more design decisions, or maybe software requirements (not that there's a big difference <grin>), than they are requirements at the product level, but they are things we identified as necessary for the Advanced Calculator to work correctly and be usable.

Team Process

We spoke by phone on Friday, July 2, and agreed that Elizabeth would design and set up the webspace for the Green Team's projects. This was completed on Saturday, July 3.

We emailed several times during development, and spoke by phone once more.

Janey wrote, commented, and tested the code. She made it look like a physical calculator, and even included one of the theme colors from the Green Team project site. She emailed Elizabeth with a couple of concerns about its functioning and questions about its look. Elizabeth tested it as well, said it seemed to work fine, and gave some suggestions for tweaking the visual design. We spoke again by phone on Tuesday, July 6, and discussed further details about the look (button alignment, etc.). Elizabeth asked for clarification about the purpose of some items in the code; Janey gave explanations, and the team discussed one or two modifications to the code.

Both team members use Dreamweaver.

Almost all of this record was written after the product was complete. Derived requirements would normally be documented as they were identified (rather than later), but in this case it is only their documentation (the writing-down, as it were) that lagged; the needed features were identified and discussed during the process.

Documentation of Product

Description

This product works similarly to a hand-held calculator that has a small number of functions. Via the computer's keyboard, the user enters a number into a text box at the top of the calculator and clicks one of the buttons to perform a calculation on the number entered. The user can clear the input at any time, by clicking the "Clear" button.

The calculator provides six functions: SQRT (square root), ABS (absolute value), EXP (exponentiation, with a base of e), LOG (natural logarithm), SIN (sine), COS (cosine), x^2 (x squared), and x^3 (x cubed).

The six function buttons are approximately the same size and are arranged in rows and columns, with related buttons beside each other. The "Clear" button is centered at the bottom, and is wider than the others.

Software Design

A function in the <head> section accepts input from the text box and returns a number to the advanced math function invoked by the button the user clicked.

Each button in the calculator invokes one built-in JS math function and stores the result in the text box, replacing any content that was there.

The Clear button sets the text input to the null string.

Lessons Learned

Typing new input into the text field without clearing it first will append the new input to the existing content in the field. I (Elizabeth) do not think it likely that the user will begin typing before clearing the existing content, but it is a potential source of error. Ideally, the field should be blanked out when it receives focus.