Computer Science

Chapter 1: Introduction to Computer Hardware

Different Categories of Computer and Computing Devices

Tablets
The lightest and most portable
Touch interface, good for “light” work

Laptops/Notebooks
Larger display area; adds CD or DVD as well as physical keyboard
They are portable; price for performance is not as good as desktop, choice of hardware is limited

Specialized Variant Laptops
Ultrabooks
Thinner, and lighter than laptops
Cost is higher than laptop (all hardware being equal)
Netbooks
Cheaper more portable laptop that is smaller and has a lower quality display and overall less powerful hardware
Much less common than tablets today

Desktop Computers
Everything is separate (monitor, computer, keyboard, etc); this allows you to mix and match and customize your desktop computer, at the cost of increased complexity (some compatibility issues may arise – not everything works together) and decreased portability.
Larger ‘footprint’ (More space is required, but this allows for increase expandability)
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Reduced costs/more options (compared to laptops)

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The purpose of an operating system is to run the computer. The operating system determines the interface of a computer, its configurability, and its security. In general, due to popularity and tweak-ability, the MS-WINDOWS (PC) OS has more viruses than the MAC OS. In general, the MAC OS is -----viewed to be more user friendly.

Large Units of Measurement and Storage
On the computer, all information is stored in binary (2 states, ON OR OFF). A single on/off combination is referred to as a ‘bit’ (binary digit).
The amount of information that can be stored and transferred is typically measured in bytes rather than bits. IMPORTANT: 8 BITS = 1 BYTE

KILObyte (KB) – 210 bytes a THOUSAND bytes (1,024 bytes)
MEGAbyte (MB) – 220 bytes a MILLION bytes (1,048,576 bytes)
GIGAbyte (GB) – 230 bytes a BILLION bytes (1,073,741,824 bytes)
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TERAbyte (TB) – 240 bytes a TRILLION bytes (1,099,511,627,776 bytes)

CPU: Central Processing Unit
The ‘brains’ of the computer; the CPU determines the program execution speed and the calculation speed
Benefits of a faster CPU include programs are loaded faster, viewing videos may be faster and more glitch free, and calculations are completed more quickly.

The CPU CLOCK SPEED is the most common technical specification of CPUs. The CPU clock speed is the speed at which the processor operates (oscillates). Typical home-type computers operate in the single low digit GIGA-clock speeds from 1-4GHz.

The number of CORES determines how many tasks that a computer can execute at the same time. Having a processor with multiple cores can speed up execution even if only a single hardware intensive program is running (the program may be written specifically to take advantage of multi-core technology). By checking ‘system requirements’ or ‘technical requirements’ on the packaging/website of a program, one may determine what is necessary to execute the program.

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Will multiple cores always be faster? It depends. To see for yourself, look at actual computer usage (Task Manager in Windows, Activity Monitor in Mac OS-X).

Memory (RANDOM ACCESS MEMORY – RAM)
When a computer program is executed, the instructions as well as any data currently needed is loaded into RAM from the storage device.
RAM is temporary storage which is gone when you turn off your computer. RAM is significantly more expensive than any other storage device.
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RAM is in GB and ranges from >4GB for basic tasks, 4-8GB for multi-tasks and some complex programs, and 10GB> for extensive multi-tasking with complex programs.

STORAGE
All data that’s needed in the long term must be kept in some form of storage. Long term storage is kept in hard drives.
There are two types of hard drives
1 – Magnetic
2 – Solid State.
Magnetic Hard Drives ardHare the slower of the two but less expensive. They are prone to magnetic field disruptions and are generally viewed as less durable due to the fact that they have moving parts.
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Solid State Hard Drives are faster (roughly twice as fast) than Magnetic Hard Drives. They are more expensive and have lower maximum storage capacity. They are more durable, and have no moving parts.

Common Computer Ports
Ports are computer connections to external devices.
Some common computer ports include: USB (standard) USB 3.0 HDMI (allows display on a TV monitor or connections to peripherals) SD Other Important Ports (for video, audio, network)

Chapter 2: Logic

There are two types of Expressions:
Mathematics (produce a numerical result)
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Logic (produce a Boolean result; can only be true or false).

Logical Operators
Similar to mathematical operators, logical operators take one or two inputs and produce an output.

TRUTH TABLE

Column 1 | Column 2 | Result of (Column 1) OPERATION (COLUMN 2) | FALSE | FALSE | TRUE OR FALSE | FALSE | TRUE | TRUE OR FALSE | TRUE | FALSE | TRUE OR FALSE | TRUE | TRUE | TRUE OR FALSE |
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Logical AND
The popular usage of the logical AND applies when ALL conditions have been met. Truth table (AND) | C1 | C2 | C1 AND C2 | False | False | False | False | True | False | True | False | False | True | True | True |
Logical OR
The correct everyday usage of the logical OR applies when ATLEAST one condition is met. Truth table | C1 | C2 | C1 OR C2 | False | False | False | False | True | True | True | False | True | True | True | True |
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Logical NOT
The everyday usage of logical NOT negates (reverses) a statement. Truth table | S | Not S | False | True | True | False |

Chapter 3: Spreadsheets

Background
Electronic spreadsheets evolved out of paper worksheets. Calculations were manually calculated and entered in columns and rows on paper often draw with grids.

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Templates are pre-created spreadsheets for many types of problems.

Worksheets are sub-pages under spreadsheets. Each spreadsheet can consist of multiple worksheets. Rule of thumb to use worksheets: When there are multiple sheets of related information, each group of information can be stored in its’ own worksheet (can be self-containted). If the information consists of groups of unrelated information, then the information about each group should be stored in a separate spreadsheet/workbook rather than implementing it in a spreadsheet with multiple worksheets.

One worksheet can refer to information stored in another worksheet. Formula for cell when referencing another worksheet =(Sheetx!Cell)

One spreadsheet can refer to information stored in another spreadsheet.

Why use cross reference?
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A typical reason why one worksheet may reference to other worksheets or spreadsheets is that the reference contains data that needs to be “looked up”.

The Excel Ribbon
Tabs are used to group related functions.
Examples of tabs: 1). File Functions associated with documents (creating, opening, saving, printing) 2). Home (default tab) Many of the most commonly used functions (formatting fonts, cells, numerical data) 3). Insert Tables, illustrations, apps, charts, graphs, text, and symbols 4). Page Layout Page setup 5). Formulas Location and groupings of the pre-created built-in mathematical formulas. 6). Data Arranging, organizing, existing data 7). Review Spell checking, thesaurus, translation, adding comments, and change tracking 8). View
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Workbook Views, Show, Zoom, Window, and Macros

Freezing Panes Often used to lock the view so that crucial labels always stay onscreen regardless of which part of the sheet you are viewing. It is found under the File table on the Excel Ribbon.

Tags
When saving work ‘saving as’, you may enter tags. These are separate from the file name but may be used as a search criteria.
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Contents of a Cell
Raw data: also known as constants 1, 2, 150
Labels: describe the contents of another cell Term percentage, Letter
Formula: Values derived from the raw data
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=formula(stuff)

Basic Mathematical Operators
(Mathematical Operation, Excel Operator)
Assignment =
Addition +
Subtraction –
Multiplication *
Division /
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Exponent ^

Designing Spreadsheets: Rules of Thumb
1). Do not directly enter values as data that can be derived from other values.
2). Label information so it can be clearly understood.
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3). Never enter the same information more than once.

Lookup Tables
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Look up tables contain the information that needs to be referred to (looked up) in a part of the spreadsheet. It can be used to address clarity and the issue of entering the same data multiple times.

Formatting Cells
Excel provides the ability to format the spreadsheet in various locations of the ribbon.
Another way to format cells is to highlight cells and right click, and select “Format Cells”.

Order of Operation Level | Operation | Symbol | 1 | Brackets (inner before outer) | () | 2 | Exponent | ^ | 3 | Multiplication, Division | * / | 4 | Addition, Subtraction | + - |
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Basic Statistics
=sum()
=average()
=min()
=max()
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Counting Functions
All counting functions tally up the number of cells that do or do not contain a certain type of data. General usage =function(<start cell range>: <end cell range>)
=Count()
Counts the number of cells within the specified range that contain numbers
=Counta()
Counts the number of cells within the specified range that aren’t empty (data)
=Countblank()
Counts the number of empty cells within the specified range

Conditional Counts
=Countif()
Counts the number of cells that meet a particular requirement
=Countifs()
Counts the number of cells that meets all in a series of multiple requirements Format: =countifs(<range 1>, <criteria 1>, … <optional additional range>, <optional additional criteria>)

Strings
Strings are a series of characters which include alphabetical characters, numerical digits, and special characters such as space, punctuation, or other symbols. String is another name for text.

EXCEL STRING FUNCTIONS (Functions that act on strings)

Converting or changing alphabetical text
=lower() converts text into lower case letters
=upper() converts text into upper case letters
=proper() converts text into proper case (first letter uppercase, rest lower)

Processing Text
=trim() removes spaces from text

Connecting Text
=concatenate() connects string or part of string with another string Example: title with surname

Extracted Portions
=left/right() extracts the specified number of characters from the left/right side of the specified string =left/right(<string>, <length>)
=mid() starting at the specified position, the function extracts the specified number of characters from the string =mid(<string>, <start>, <length>)
=find() finds the starting position of one string with another string =find(<find text>, <within text>, <start position>)

Why bother?
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It saves labor (saves time and effort). Different views of the same data may be needed. It may be useful to be familiar with these functions for the future.

Date and Time Functions
=today() displays the current date (month/day/year)
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=now() displays the current date (month/day/year) and the time (hour/minute) with a 24 hour clock

If-Else Branching
=if( <condition to check>, <return value if true>, <return value if false>) If functions use Boolean inputs (logic). They can only deal with true or false outcomes.

Logical Comparators Math | Excel | Meaning | < | < | Less than | > | > | Greater than | = | = | Equal to | ≤ | <= | Less than, equal to | ≥ | >= | Greater than, equal to | ≠ | <> | Not equal to |

If: Specifying only the True Case
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If only a return value for the true case has been specified, then when the condition has not been met, FALSE will be displayed.

Nested Conditions
Nested conditions are conditions that are dependent upon or are affect by previous conditions. Nesting refers to conditions that are inside other conditions.

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=IF( <condition to check>, <return:true>, <another IF for the false return>)

LOOKUP
Typical use for LOOKUP includes looking up a value from one column (a vector), and returning a value from another column (a vector).

=LOOKUP ( (Cell contains value to find in a table), (Lookup column), (Result Column) )

Example:

=LOOKUP(D2, D11:D15, E11:E15

In this case, we are looking at the term grade points found in the ‘D2’ column, which then according to our lookup table has data stored in the ‘D’ and ‘E’ columns which we are looking to return.
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Lookup tables can be used instead of many nested ‘if’ conditions. Here, we are assigning IF functions to each condition that the lookup table has defined.

VLOOKUP
VLOOKUP is a more complicated and more powerful version of a lookup function. It is basically a LOOKUP function with an extra argument that allows for T/F. Option Value = True True works like LOOKUP; Looks for an appropriate match, if an exact match is not found, the next largest value that is less than the lookup value is returned. If the T/F value is omitted then the function assumes a ‘true’ value.

=VLOOKUP( <lookup value>, <lookup table start:end>, <lookup table column specifying return value>, <exact match?>)

Use TRUE when looking for a value in a range of values; tax brackets, grades… etc
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Use FALSE when there is an exact value to lookup; SIN numbers, product ID number … etc

Logic Operations in Excel
The basic logical operations can be invoked as functions in excel.

AND(<true or false>,<true or false>,…)
OR(<true or false>, <true or false>,…)
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NOT(<true or false>)

Methods of Referring to Cells
Absolute
The formula won’t change if you copy/cut and paste the formula or if the spreadsheet changes in size. Absolute cell references are specified with a $ sign.

Relative The formula changes depending how far that the formula is moved or how much the spreadsheet is changed in size.

Testing Spreadsheets
You should test formulas to ensure that they are correct.
Enter a few test values and see if the results match expectations.
Baseline test cases you could use: 1. Nothing to invest (principle = 0) 2. Interest rates are 0. 3. No time passed. 4. -------------------------------------------------
Normal case: Non zero values for: principle, interest, or time.
Testing Ranges
The following are minimum test cases.
They provide test values in each range.
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Example: Min. GPA; 0,1,2,3,4 – Fail, Pass, etc

Graphic Design and Spreadsheets
Using Color
When used sparingly, color can draw attention to important information. This is an especially valuable tool when there is a large amount of information.
The overuse of color: -reduces its ability to make information stand out -makes it harder to understand what information is mapped to a particular color.
Rule of thumb for color: Make it SUBTLE Balance the use of color between noticeability and subtlety.

Issues with Color: Color blindness affects a portion of the population; the majority of the color blind cannot distinguish red-green very well therefore avoid using them. Field Size: the larger the area to be color coded, the more easily that colors can be distinguished
Using Fonts
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Rule of thumb: No more than 3 different font types in a particular document.

C.R.A.P. CONTRAST REPITION ALIGNMENT PROXIMITY Simple design principles that can be applied in a variety of situations.
Contrast & Repetition: Contrast: make different things look significantly different Repetition: Repeat conventions throughout the interface to tie elements together.
Alignment:
It can be used to structure a document (may demonstrate hierarchical relationships). Center Alignment: Don’t use it for hierarchical documents because it hides or removes the organization. At most: sparing use can be used to provide contrast.
Proximity:
Related items are in close proximity.
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Unrelated items are separated.

Text vs. Graphics Text is the best representation to use when accuracy is paramount.
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Graphics are best useful for illustrating relationships or visualizing patterns.

Pie Charts
Good for showing proportions, how much of the whole does each item contribute. It is poor for showing numerical values.

Bar and Line Graphs
Good for showing trends and comparing functions.

Rule of thumb for graphs: The X axis is used to plot known data, while the Y axis is used to plot the unknown data. Bar graphs are used to plot NON CONTINOUS DATA. Line graph are used to plot CONTINOUS DATA.

Chapter 4: Databases

Databases
The purpose of a database is to store and retrieve information. We use databases when storing data becomes complex or the lists become long.
Columns:
------------------------------------------------- Columns are the attributes that we track for each record. They are “Fields” in Access. Primary Key Each table should typically have one attribute designated as the primary key. The primary key must be guaranteed to be unique. It must uniquely identify one record from another. Choosing a Primary Key: A primary key must be unique to each record because it is the one thing that distinguishes them. If there’s at least one instance where the attributes of two records can take the same value then that attribute cannot be the primary key. If a primary key cannot be formed from a single attribute then several attributes can be combined into a composite key.
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Example of primary key: SIN Number (Every user must have a different SIN) Viewing MS-ACCESS Design View This view is used to specify what attributes of a table will consist of. This view is also used to specify the type and the formal and valid ranges of values.

Datasheet View ------------------------------------------------- Once the attributes have been specified in the Design view, using the Datasheet view allows data entry for each record. Tables A table stores related information. Naming tables: 1. Create a unique and descriptive name. 2. Do not use words that convey database or technical terminology (file, record, table) 3. While names should be short avoid using acronyms and abbreviations (unless well known). 4. Consider using the plural form of a name. 5. Avoid the use of spaces in a name. Guidelines for Naming Attributes 1. Select a unique and descriptive name. 2. Create a name that accurately, clearly, and unambiguously identifies the characteristic that the attribute represents. 3. While names should be short, avoid using acronyms and abbreviations unless they are well known. 4. Use the singular form of a name. 5. ------------------------------------------------- Avoid the use of spaces in names. Null Values Refers to the attributes of a record that are empty. Primary keys CANNOT BE NULL but other attributes may be null. Entry of any attribute can be made mandatory. Foreign Key: an attribute in one table that refers to an attribute in another table.
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Foreign keys can prevent errors. Relationships between Tables Relationships occur when an attribute of one table is a foreign key in another table. Multiplicity: Indicates HOW MANY instances of a particular item participates in the relationship.

ONE-TO-ONE RELATIONSHIPS One entity participates in the relationship from the ‘left’ and one entity participates in the relationship from the ‘right’. This relationship is relatively rare in databases. ONE-TO-MANY RELATIONSHIPS On one side of the relationship, one entity participates in the relationship while on the other side, zero or more entities may participate in the relationship. Gamers: Sessions: Games One Gamer may have many sessions, One session many have many games. MANY-TO-MANY RELATIONSHIPS
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On each side of the relationship, zero or more entities may participate in the relationship. When there is a one to many relationship, the primary key of the ‘one’ side becomes a foreign key to the ‘many’ side. Entity-Relation diagrams (ER Diagrams or E.R.D.’s) show the attributes of a table:

TABLE NAME
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Primary key Attribute Attribute
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ERDs graphically represent relationships between tables as well as any enforced rules on multiplicity. Types of Tables Data Tables Dynamic, will likely be manipulated over the life of the database. Validation Tables Used to ensure data integrity (lookup values) Typically maps one value to another. Rarely changes.

Types of Data Integrity in Databases 1. Table-level Integrity (entity integrity) This ensures that no duplicate records exist. Implementation: no primary keys are null; no duplicates 2. Relationship-level Integrity (referential integrity) Ensures that relationship between a pair of tables is sound and the records in the tables are synchronized when data is entered into, updated in, or deleted from either table. 3. Field/Attribute-level Integrity (Domain Integrity)
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Ensures that the attributes are valid and accurate. Input Masks Input masks insure the proper format for the data entered in the database. Example: SIN numbers must be entered as <three digits> space <three digits> space <three digits> To define an input mask, switch to design view. Specify the required format under the “Input Mask” property of the appropriate table attribute. Benefits: Constrains inputs Ignores invalid inputs in real-time
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Specifies the format of data to be entered (data entry cues) Validation Rules Validation rules check the data is in the valid range. Can be used to specify a data format. The Wildcard The Wildcard is a value that can be used in place of the other values. The wildcard can be used in conjugation with validation rules. Wildcards are special characters that can stand in for unknown characters in a text value and are handy for locating multiple items with similar, but not identical data. Wild cards can also help with getting data based on a specified pattern match.
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To locate a specific item when you can’t remember exactly how it is spelled, use a wildcard character in the query. Documenting a Database Documentation provides information about the database to the other people who will be working on the database. In MS-ACCESS documentation can be entered in the “Description” column under the Design View.
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It can provide information about the type and format of the information stored. Database Queries Queries are questions asked of/to the database in order to retrieve information. Data retrieval occurs through the use of queries: Create -> Query Design Select the desire table or tables Select the attributes of the table Run the query to view the results.

SQL (STRUCTURED QUERY LANGUAGE) SQL is the universal language for querying a database. Unlike graphical queries, the staements are portable between different database programs. SELECT – Specifies the relevant attributes of which tables are involved in the query. FROM – Lists the tables from which the data is to be selected. WHERE – Provides the conditions to determine if a particular row shows or doesn’t show a result. ORDER BY – Specifies the order in which rows are to be returned