OCR A Level Computer Science Paper 2 Rated 5 star

OCR A Level Computer Science Paper 2 Rated 5 star Abstraction - a way of separating logical and physical parts of a problem e.g. the london underground map. You get rid of unnecessary details Problem abstraction - where you keep removing details until the problem reduces to one that has already been solved 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 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 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 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 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 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 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 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 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 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 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 When creating modules we should - Use meaningful identifiers (for variable names) Define and document inpu