9.2.3 Implementing

Question 1

What is the difference between a rounded rectangle and a normal rectangle in railroad diagrams?

Answer 1

Rounded rectangle indicates a literal.

A normal rectangle indicates an element that needs to be defined elsewhere.

Question 2

What do curly braces represent in EBNF?

Write down some examples of the statement a { b }

Answer 2

A repetition of the the elements inside zero or more times.

a { b } would represent: a, ab, abb, abbb etc.

Question 3

What do square brackets mean in EBNF?

Write down the possible statements defined by a [b] c

Answer 3

An option (zero or once).

a [b] c would be either abc or ac.

Question 4

In EBNF, how can you specify that an element must repeat one or more times?

For example, how could you describe

hi, hii, hiii, hiiii etc.

Answer 4

By including the element as a literal, followed by a zero or more time loop (curly brackets).

That is, h i { i }

Question 5

What are parentheses used for in EBNF?

Answer 5

As a grouping symbol, to remove any possible ambiguity in a rule.

Question 6

How do you specify a choice between options in EBNF?

Answer 6

With a vertical line.

For example, x ( + | - ) y could be x + y or x - y

Question 7

In EBNF, how do you specify a symbol that requires further definition elsewhere?

_{(This is also called a non-terminal symbol)}

Answer 7

Using angled brackets.

For example, in the rule if < condition > then, if and then are literals while condition is defined elsewhere.

Question 8

What is the only type of code that can be executed by a computer?

Answer 8

Machine code: commands written in binary that are specific to each processor (or family of processors).

Question 9

What is assembly language?

Answer 9

A low-level language that is processor-dependent. It uses text codes (“opcodes”) to perform arithmetic functions and access processor registers.

Each opcode in assembly corresponds to one machine code instruction, but is (very slightly) more readable.

Question 10

What does translation refer to?

Answer 10

The process of converting human readable (high-level) languages into machine code.

The 2 forms of translation are interpretation and compilation.

Question 11

Describe how an interpreted language is executed.

Answer 11

The interpreter executes each line of source code as it is read.

Question 12

Describe how a compiled language works.

Answer 12

A compiler analyses the entire source code and creates an executable file.

Question 13

Outline the advantages and disadvantages of compilation and interpetation.

Answer 13

Interpretation

• Advantages
  
  • Code can be run immediately (no waiting to compile) so errors are more easily identified.
• Disadvantages
  
  • Slower to execute.
  • Source code is not protected.
  • Intepreter needs to be distributed along with the source code to end users.

Compilation

• Advantages
  
  • Code typically runs faster.
  • Hard to reverse engineer - source code is protected.
• Disadvantages
  
  • Developing/testing takes longer, having to compile after each change.

Question 14

What are the 3 stages involved in translation?

Answer 14

1. Lexical analysis
2. Syntactical analysis
3. Code generation

Question 15

Outline the process of lexical analysis.

Answer 15

Each word in the source code is checked to see if it is part of the language.

The words are converted into tokens to represent parts of the langugae and user-defined variable names.

Question 16

Outline the process of syntactical analysis.

Answer 16

The source code is analysed to ensure it follows the syntax of the language.

This is achieved by creating a parse tree from the tokens generated in the previous stage. A parse tree is a visual representation of a syntactically correct statement.

Question 17

Outline the process of code generation

Answer 17

The correct parse tree containing the tokens is converted to machine code.

Question 18

What is the function of a linker?

Answer 18

In the code generation stage of translation, the linker adds any links to library files used by the source code.

Question 19

What is a DLL?

Answer 19

A dynamically linked library, which contains compiled library functions that can be used by other programs. DLLs are accessed at run time, compared to static libraries which are compiled with the source code.

Question 20

Outline the three types of errors that can occur.

Answer 20

1. Syntax errors - incorrect use of the programming language
2. Logic errors - syntactically correct code that does not meet the objective of the code.
3. Runtime errors - errors that occur during the execution of the program.

Question 21

Outline the 3 types of runtime errors that can occur

Answer 21

1. Arithmetic overflow - when a value is assigned outside a the range allowed for that data type.
2. Dvision by zero
3. Accessing inappropriate memory locations - attempting to access an array index beyond the length of the array for example.

Question 22

What hardware requirements must be considered when implementing a software solution?

Answer 22

• Requirements of existing hardware, like amount of RAM/hard disk space and CPU.
• Additional software needed, like graphics card/sound card, or peripherals like a barcode scanner.
• Software drivers to communicate with required hardware.

Question 23

Related to hardware, what is a driver?

^{*As opposed to a driver related to <em>testing a subroutine or library module</em>}

Answer 23

Software that allows a computer program to operates or controls a particular type of hardware device

Question 24

How might CASE tools be used to produce different types of documentation for a software solution?

Answer 24

CASE tools would likely not be used for user documentation (eg user manual, installation guide etc).

CASE tools could be used for technical documentation such as:

• Source code
• Algorithms
• System models
• Documentation of changes

Question 25

Outline 4 software tools for error detection & correction

Answer 25

1. Breakpoints - pause execution of the program at a particular line of code.
2. Single line stepping - controlling the flow of execution, one line at a time.
3. Resetting variables - editing the values of variables during execution.
4. Program traces - any kind of program tracking. This could be the statements

Question 26

Outline 5 types of user documentation

Answer 26

1. Installation guide - steps for installing the program
2. User manual - instructions on how the use the program, generally presented in an appealing way. Possibly organised to cover common and easier tasks before moving on to more advanced topics.
3. Reference manual - not designed to be read through. Possibly organised alphabetically for efficient access.
4. Tutorials - a set of steps to achieve a specific outcome.
5. Online help - link to any of the above via the internet.

Question 27

Outline 3 types of technical documentation

Answer 27

1. Log book - document the processes and decisions made in development.
2. Comments in source code - documenting purpose of subroutines and arguments/return values, details of specific logic, etc.
3. Intrinsic documentation - variable names, indentation, etc.