Spreadsheets and Databases Class 8 LBSC 690 Information Technology

Agenda Questions Spreadsheets Database design

What’s a Spreadsheet? Large table containing numbers –May also contain labels to aid interpretation –Columns are named with LETTERS –Rows are named with NUMBERS –Cells are named like A4, C1,... Some cells are automatically calculated –Formula specified when spreadsheet is created –Values are recalculated continuously

How Spreadsheets are Used Record keeping (cassette tapes) Calculation (income tax) What-if analysis (cash flow) –Sensitivity analysis (exchange rate) Goal seeking (retirement planning) –Uses continuous recalculation (“iteration”)

How Spreadsheets are Used Record keeping (cassette tapes) Calculation (income tax) What-if analysis (cash flow) –Sensitivity analysis (exchange rate) Goal seeking (retirement planning) –Uses continuous recalculation (“iteration”)

Spreadsheet Applications Originally designed for financial records Library applications –Budget –Collection development –Shelving capacity Educational Applications –Grade records –Equipment inventory

Excel Demo Start Excel –Microsoft Office folder Open N:\SHARE\CLASS\POSTCARD.XLS –File menu Enter your 1997 (desired) income in cell B3 –Tax due is displayed in cell B4

Excel Demo Change the tax due –Place the cursor over B4 –Type “=B3*0.x” “=” tells Excel this is a formula “B3” refers to the number in cell B3 The “x” in “0.x” should reflect your political views –0.5 would take away half your money –Try different values in cell C3 What kind of spreadsheet use is this?

Excel Demo Add itemized deductions –Highlight row 4 (click on 4) –Select “Row” in “Insert” menu twice –Label A4 as “Deduction amount” –Label A5 as “Taxable income” –Put the appropriate formula in B5 –Change the formula in B6 as needed Note how it was copied from B4 with changes

Excel Demo Limit the deduction –Maximum of 50% of income or 10,000 Search for help on “maximum” Replace the formula in B5 with a more complicated one –You can use another cell to show a partial result

When Style is Important Too complex to visualize at once –Size –Relationships between formulas Used by more than one person –Includes use in presentations and papers Used for a long time –Essentially communicating to yourself

Style Guidelines Organization –Depict the solution approach visually –Group things where possible (e.g., parameters) –Build in cross-checks to discover input errors Readability –Describe the computation –Meaningful labels help a lot –Minimize clutter

Building Complex Applications Computers keep track of detail well –But people don’t Adopt meaningful abstractions –Organize a calculation the way you think Use a structured process –Examples: waterfall and spiral models

Relational Databases Tables represent relations –Name, project –Name, address, phone number Relations can be “joined” –Name, project, address, phone number Relations can be “projected” –Name, address Relations can be “restricted” –Name = “Doug Oard”

Why use Join? Forces consistency –Doug Oard, project 18, –Doug Oard, project 22, Limits the chance of error –Doug Oard, project 18, –Doug Oard, project 19, Avoids lots of duplicated entry and updates Can save a lot of storage space

Problems with Joins Data modeling for joins is complex –Taught in LBSC 670 Joins are expensive to compute –Both in time and storage space But it is joins that make databases relational –Projection and restriction also used in flat files

Key Fields Primary Key uniquely identifies line to join –May group several fields to get a unique key Social security number First and last name “Foreign” key must appear in the other table –But it need not be unique there Join makes a new table –Line specified by foreign key is tacked on

Example of a Join on “Team” Name Team Project NameTeamProject Chris Camile Eileen Natalie David Tonya Michelle Skip A A A B C B C C A B C Database Web A A A B C B C C Chris Camile Eileen Natalie David Tonya Michelle Skip Database Web Database

Project to Keep Two Fields Name Team Project NameProject Chris Camile Eileen Natalie David Tonya Michelle Skip A A A B C B C C A B C Database Web Chris Camile Eileen Natalie David Tonya Michelle Skip Database Web Database

Restrict to Web Pages Name Team Project NameProject Eileen Natalie David Tonya Skip A A A B C B C C A B C Database Web Chris Camile Eileen Natalie David Tonya Michelle Skip Web