# OCR AS ICT Unit 1 Chapter 4

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• Created by: Sqd3
• Created on: 18-04-14 11:55

## Chapter 4 - Modelling

Types of Modelling:

• Modelling of Objects:
• Creates a virtual representation - Model large items (e.g. building) and look at them from different external factors. (e.g. surface and environment).
• View different layers - E.g. exterior and interior.
• What-If questions can be asked - Components can be changed to see how it reacts.
• Mathematical Modelling:
• Based on functions and formulae - Allows the input of numbers into spreadsheets and for any changes to be automatically recalculated.
• Use of Graphs - To spot trends in data.
• Based on rows and columns - Items are laid out in a logical format and leads to sequencing and replication.
• What-if questions can be asked - User can change variables/values and see what the effect would be on the end result.
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## Chapter 4 - Modelling

Why computer modelling is used:

• Less Risk, safer and cheaper to test a model than to create it in reality and test it.
• One model is created - a real model would would cost time and money (due to alterations).
• Can be backed up and shared.
• Can be sped up/slowed down.
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## Chapter 4 - Variables, Rules & Functions

• Variables:
• Identifier associated with a particular cell that contains a value (that can change)
• e.g. a cell reference, name.
• The value within the variable is used in a function/formula
• Formulae:
• An expression that allows calculations to be represented in a spreadsheet.
• It uses numbers, cell addresses and mathematical operators.
• If cells in the formula change then the formula will recalculate in response to the change.
• Rules:
• Set of procedures that must be followed
• Can also be the sequence of events required for the calculation to work.
• Functions:
• Predefined, complex formulae that represent standard routines used to perform common tasks e.g. SUM, MAX, MIN, AVERAGE etc
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## Chapter 4 - 'What-If?' Questions

'What-if?' questions are an attempt to find out what will happen in the future. Calculations are done within the spreadsheet or data model to help answer them.

• Models can automatically recalculate data.
• Unlimited number of 'what-if' questions can be asked.
• Custom interfaces can be built to increase usability.
• Time and cost are reduced as physical models could be costly.
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## Chapter 4 - Components of Spreadsheets

Workbook: A set of linked worksheets in the same spreadsheet. (Use: To divide and organise data into different categories between the sheets.)

Worksheet: A grid of cells on a single sheet. (Use: To hold data on a single area of a business.)

Row: A horizontal group of cells. (Use: To organise data)

Column: A vertical group of cells(Use: To organise data)

Cell: An individual data store uniquely identified by a column and row indicator. (Use: Can be formatted (e.g. colour) and protected (to prevent altered data)).

Range: A group of cells that can be given a name or identified by their cell references. (Use: To contain similar data).

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## Chapter 4 - Cell Referencing

Absoloute Cell Referencing - When the cell referenced in a formula remains the same when the formula is copied to other cells.

• Achieved by adding "\$" before the column letter and row number. E.g. \$A\$2

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Relative Cell Referencing - When the cell reference in a formula changes when the formula is copied to other cells.

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## Chapter 4 - Spreadsheets to run simulations

Computer Model - Comprises a set of data about something and a set of rules that control what the data does.

• Automatic recalculation - A change in the cells then all formulae and values change.
• Graphs can be produced - Automatically change as any values change.
• "What-If?" questions can be asked.
• Quicker and cheaper than real life models.

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