C. Demetriou (2009)        November 1, 2009      1




ž Modelling of objects
ž Modelling of Data




                    ...
ž   Allows you to create virtual
    representations of objects
    such as :-
        › Buildings
        › Cars
ž   You ...
ž The ability to ask questions of the model.
ž Changing components to see the effect
  or how it reacts.
ž Effects can be ...
ž   What features make
    spreadsheets ideal for
    modelling?
    › Functions
    › Formulae
    › Variables
    › Auto...
ž   These are special types of formulae used in a
    spreadsheet

ž   They are used to represent formulae that may
    be...
ž   Answering ‘what-if?’ questions
    › A model can recalculate values – this allows
      single values to be changed an...
ž   Worksheets and Workbooks
     › A number of worksheets within a single file is called a workbook. A
       workbook ca...
A     B         C          D            The formula in Cells
                                                   C2:C4 is r...
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AS ICT (OCR) G061 3.1.4 Spreadsheet Concepts lesson slides

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AS ICT (OCR) G061 3.1.4 Spreadsheet Concepts lesson slides

  1. 1. C. Demetriou (2009) November 1, 2009 1 ž Modelling of objects ž Modelling of Data C. Demetriou (2009) Nov ember 1, 2009 2
  2. 2. ž Allows you to create virtual representations of objects such as :- › Buildings › Cars ž You can look at the effect of outside influences. › Impact › Earthquakes › Fire › Explosions C. Demetriou (2009) Nov ember 1, 2009 3 ž Possible to see different layers › Internal View › External View › Wireframe › Electrical systems C. Demetriou (2009) Nov ember 1, 2009 4
  3. 3. ž The ability to ask questions of the model. ž Changing components to see the effect or how it reacts. ž Effects can be gauged at the touch of a button. ž Without having the risk of building the real thing. C. Demetriou (2009) Nov ember 1, 2009 5 ž Mathematical modelling ž Predictions in Finance › Using spreadsheets › Allows replication of values › Allows sequences to be setup › Allows What If Scenarios to be modelled C. Demetriou (2009) Nov ember 1, 2009 6
  4. 4. ž What features make spreadsheets ideal for modelling? › Functions › Formulae › Variables › Automated calculations (refreshed) › Great for trying out different scenarios C. Demetriou (2009) Nov ember 1, 2009 7 ž Variables › An identifier associated with a value stored in the model. The value may be in a cell or in memory ž Formulae › Formulae allow calculations to be represented in a spreadsheet. As well as numbers, a formula uses the addresses of cells to identify other values to be used. The result is placed in the cell in which the formula was placed › If any of the cells used on the formula change their value, the result of the formula is updated – E.g (I2-2*B3)/2 C. Demetriou (2009) Nov ember 1, 2009 8
  5. 5. ž These are special types of formulae used in a spreadsheet ž They are used to represent formulae that may be too large or complex for the ordinary user to enter: › SUM() – to add a range of numbers › AVERAGE() – to calculate the average of a range › HLOOKUP() – to find one value based on another in a horizontal list › VLOOKUP() – to return a value based on another in a vertical list › IF() – to make a decision based on a value and give an answer whether its TRUE or FALSE C. Demetriou (2009) Nov ember 1, 2009 9 ž Rules are a set of procedures that must be followed. For example, if a calculation requires two values, then these values must be supplied. ž Validation rules ensure that data entered meets a criteria or is present. ž Could be coding:- For each cadidate For each module Enter a UMS mark Add all the marks together Lookup the mark in the grade table Return a grade C. Demetriou (2009) Nov ember 1, 2009 10
  6. 6. ž Answering ‘what-if?’ questions › A model can recalculate values – this allows single values to be changed and the rest of the model to be updated automatically › Various combinations can be tried with minimal effort › ‘What if’ questions are predictive by nature ž Advantages of using a data model for ‘What if?’ questions: › Only one model needs to be created and then altered › Many different possibilities can be tried - repeatability › Mistakes can be eradicated prior to construction › Cost of creating a changeable model against several different models › Safety of the model – nuclear explosion, trip to Mars. Virtual Vs Physical models. › Control over the variables C. Demetriou (2009) Nov ember 1, 2009 11 ž Drawbacks of using spreadsheets to create or run a spreadsheet › Model may not be an accurate representation of the real world. › If the model relates to people then an accurate result may not be given. › Many Variables need to be considered and it is easy to miss things out. › Producing effective models can take a lot of time and may need expensive hardware and software. C. Demetriou (2009) Nov ember 1, 2009 12
  7. 7. ž Worksheets and Workbooks › A number of worksheets within a single file is called a workbook. A workbook can be used to divide information between different sheets, for example income on one sheet, expenditure on another, and a summary on a third ž Rows › Rows are a horizontal group of cells. In Excel they are identified by Number ž Columns › Columns are a vertical groups of cells. In Excel they are identified by Letter ž Cells › A cell is the square on a spreadsheet in which only a single entry can be placed. The entry can be text, numbers or a formula. It can be referred to by its address based on its row and column ž Ranges › A range is a group of cells – usually identified by the address of the top left cell to the bottom right cell: A1:G5 for example C. Demetriou (2009) Nov ember 1, 2009 13 ž Replication is the process of copying a formula from one cell to another › As a formula usually involves references to cells, it is necessary to know whether you want to keep the references the same (absolute reference) or change according to the row or column movement (relative reference) ž An absolute reference always refers to the same cell. Anchors are created using $ sign eg. $A$3. Anchors are needed on either Rows or Columns. ž A relative reference changes the cell it references according to the movement of the target cell. There are no anchors on relative references such as A3 C. Demetriou (2009) Nov ember 1, 2009 14
  8. 8. A B C D The formula in Cells C2:C4 is replicated using both relative and 1 Good Price VAT Payable VAT absolute replication. 2 Pen £50 =B2*$D$2 17.5% When the cell is replicated down, the reference to B2 needs 3 Watch £200 =B3*$D$2 to change so that the price changes. 4 Ring £500 =B4*$D$2 However, the reference to cell D2 cannot change. If it was to change to cell D3 the formula would not work, as there is nothing in cell D3. Therefore as C2 is replicated, the reference to B2 needs to change, hence it is a relative reference, but the reference to D2 must not change, so it is absolute. C. Demetriou (2009) Nov ember 1, 2009 15 ž Form Controls › They include items like: – Spinners – Drop down boxes – Buttons › They are used to increase the usability of the spreadsheet – list/drop down boxes can limit data entry, making validation easier! › Buttons can run Macros C. Demetriou (2009) Nov ember 1, 2009 16

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