OCR A Level Computer Science Paper 2
1. Abstraction: a way of separating logical and physical parts of a problem e.g.
the london underground map. You get rid of unnecessary details
2. Problem abstraction: where you keep removing details until the problem
reduces to one that has already been solved
3. Modelling and Simulation: Building a model of a real world object can be
used to solve a particular problem such as Aircraft simulation, Climate change
models
4. Precondition: is the logic part of a statement statement that has to be true for
the processing part of the algorithm before it can function
5. Specifiying a precondition before creating an algorithm ensures: The data
is ok to process e.g. if it was empty it could cause the program to crash.
The function is reusable
It reduces unnecessary checks
It makes programs easier to debug and maintain
It makes programs clearer and shorter
6. Progamming standards that make programs easy to resuse include:
Documenting inputs, outputs and preconditions Variables should use
camelCase or PascalCase
All variables should be local to that module
The documentation should contain information such as who made it, what it does
and when it was written.
The code should be annotated where necessary
The module should not be greater than one page of code
7. Caching: the temporary storage of data instructions so that the information can
be achieved quicker than performing a calculation e.g. frequently accessed web
pages can be stored locally
8. The advantages pf caching: It's faster to access information that is cached
This saves the cost of bandwidth
It also reduces the load on web services in a client-server environment
9. Disadvantages of caching: There is slower performance if the result is not
found in the cache
Sometimes the cache can be "stale" meaning that it doesn't contain the latest
updated data. E.g. When using a cached database on available products you
might think an item is still available when it is actually not
, OCR A Level Computer Science Paper 2
10. Decomposition: This is where a problem is broken down into a number of
subproblems so that each subproblem completes a part of the bigger problem
11. Structured Programming: This is where the aim is to improve the quality
of a program by -
Modularization - Breaking the program down into subroutines
Structured Code - The subroutines should use sequence, selection and iteration
Recursion
12. Top Down Design Model: A program can have many sub-procedures which
are called from the main program and these sub-procedures can also have
sub-tasks and so we use a hierarchy chart to show the overall program
structure.
When following a hierarchy chart we execute from the left to the right
13. Benefits of modularisation: Large problems are broken down into smaller
problems which are easier to manage
Each subroutine (module) can be easily tested
Modules can be reused several times in a program
Frequently used modules can be saved in a library and used by other programs
Lots of programmers can work on different modules at the same time saving time
It is easier to find errors taking less time to debug
Programs are easier to maintain
14. When creating modules we should: Use meaningful identifiers (for variable
names)
Define and document inputs, outputs and preconditions
Add meaningful comments
Make them self contained by passing parameters and using local variables
15. An Algorithm should: Have clear and precise steps that produce a correct
output for any valid input. Allow for invalid inputs
Terminate at some point
Execute in as few steps as possible
Be understandable by other people so that they can modify it
16. To help design algorithms we use these solutions: Hierarchy Charts -
Used
to identify major tasks and breaking them down into sub tasks
Flow Charts - Used to work out individual subroutines
Pseudocode - Used to translate easily into program code
1. Abstraction: a way of separating logical and physical parts of a problem e.g.
the london underground map. You get rid of unnecessary details
2. Problem abstraction: where you keep removing details until the problem
reduces to one that has already been solved
3. Modelling and Simulation: Building a model of a real world object can be
used to solve a particular problem such as Aircraft simulation, Climate change
models
4. Precondition: is the logic part of a statement statement that has to be true for
the processing part of the algorithm before it can function
5. Specifiying a precondition before creating an algorithm ensures: The data
is ok to process e.g. if it was empty it could cause the program to crash.
The function is reusable
It reduces unnecessary checks
It makes programs easier to debug and maintain
It makes programs clearer and shorter
6. Progamming standards that make programs easy to resuse include:
Documenting inputs, outputs and preconditions Variables should use
camelCase or PascalCase
All variables should be local to that module
The documentation should contain information such as who made it, what it does
and when it was written.
The code should be annotated where necessary
The module should not be greater than one page of code
7. Caching: the temporary storage of data instructions so that the information can
be achieved quicker than performing a calculation e.g. frequently accessed web
pages can be stored locally
8. The advantages pf caching: It's faster to access information that is cached
This saves the cost of bandwidth
It also reduces the load on web services in a client-server environment
9. Disadvantages of caching: There is slower performance if the result is not
found in the cache
Sometimes the cache can be "stale" meaning that it doesn't contain the latest
updated data. E.g. When using a cached database on available products you
might think an item is still available when it is actually not
, OCR A Level Computer Science Paper 2
10. Decomposition: This is where a problem is broken down into a number of
subproblems so that each subproblem completes a part of the bigger problem
11. Structured Programming: This is where the aim is to improve the quality
of a program by -
Modularization - Breaking the program down into subroutines
Structured Code - The subroutines should use sequence, selection and iteration
Recursion
12. Top Down Design Model: A program can have many sub-procedures which
are called from the main program and these sub-procedures can also have
sub-tasks and so we use a hierarchy chart to show the overall program
structure.
When following a hierarchy chart we execute from the left to the right
13. Benefits of modularisation: Large problems are broken down into smaller
problems which are easier to manage
Each subroutine (module) can be easily tested
Modules can be reused several times in a program
Frequently used modules can be saved in a library and used by other programs
Lots of programmers can work on different modules at the same time saving time
It is easier to find errors taking less time to debug
Programs are easier to maintain
14. When creating modules we should: Use meaningful identifiers (for variable
names)
Define and document inputs, outputs and preconditions
Add meaningful comments
Make them self contained by passing parameters and using local variables
15. An Algorithm should: Have clear and precise steps that produce a correct
output for any valid input. Allow for invalid inputs
Terminate at some point
Execute in as few steps as possible
Be understandable by other people so that they can modify it
16. To help design algorithms we use these solutions: Hierarchy Charts -
Used
to identify major tasks and breaking them down into sub tasks
Flow Charts - Used to work out individual subroutines
Pseudocode - Used to translate easily into program code
