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Chapter 9: Sample Applications
Outline Spreadsheets Databases Numeric and
Symbolic Computations
Computer NetworksAlgorithmic Foundations
Hardware
Virtual Machine
Software
Applications
Social Issues
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Spreadsheets An electronic spreadsheet combines elements of:
a calculator a word processor a database manager a graphing tool a modeling tool …
Spreadsheet programs: Widely used Examples:
VisiCalc MS Excel
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Spreadsheets A spreadsheet is a 2-dimensional grid of cells:
Rows: 1, 2, 3, … Columns: A, B, C, …
Only a portion of the spreadsheet in visible on the screen
window Window can be scrolled down/up
Cell: specifies a row and a column: Activated using mouse or cursor Example:
D2 means the cell at 2nd row and 4th column
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Spreadsheets Information in each cell may be:
Label Numeric value Mathematical formula
Labels Text information that appear on the screen in a cell Any cell can contain a label (row numbers and columns
letters are also labels) Format can be chosen: Font size, boldface, … Example
A B C D E1 Item1 Item2 Total labels
2 3.25 5.75 9.00 numeric values
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Spreadsheets Numeric values:
Like labels can be formatted e.g. only 2 digits after the decimal point negative value in parentheses
Mathematical formulas Do not appear on the screen Entering a formula usually require some extra keystroke be
done first Example:
C2 = A2 + B2 Total (C2) is computed automatically Error message if A2 or B2 are not numeric values
Example: Payroll of a company
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SpreadsheetsA B C D E F G
1 ID Name Age Rate Hours Pay
2 101 Janet K 51 16.60 94
3 102 Adam R 18 8.50 185
4 103 Fred L 43 12.35 250
5 104 John A 53 17.80 245
6 105 Butch H 17 6.70 53
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Pay of Janet D2*E2 formula needed for Pay Entering the formulas:
Enter D2*E2 in cell F2 Copy (automatically supported) to other cells in column F
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Spreadsheets What you enter: (formulas entered)
A B C D E F1 ID Name Age Rate Hours Pay
2 101 Janet K 51 16.60 94 D2*E2
3 102 Adam R 18 8.50 185 D3*E3
4 103 Fred L 43 12.35 250 D4*E4
5 104 John A 53 17.80 245 D5*E5
6 105 Butch H 17 6.70 53 D6*E6
What you see: (values computed)A B C D E F
1 ID Name Age Rate Hours Pay
2 101 Janet K 51 16.60 94 1560.40
3 102 Adam R 18 8.50 185 1572.50
4 103 Fred L 43 12.35 250 3087.50
5 104 John A 53 17.80 245 4361.00
6 105 Butch H 17 6.70 53 355.10
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Spreadsheets Other Features
Built-in functions for: Average Maximum Minimum User selects the desired cells and apply function
Graphics: Data can be presented in graphical form Line graph Bar graph Pie graph etc.
Multiple sheets can be handled at one time Formulas can be propagated to all sheets in use (if
possible) Create 3-dimensional sheets
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Spreadsheets Other Features (contd)
User can write macros Macro:
A series of instructions called by name “Like” a function … The name serves as a shortcut notation Use of macros saves time
Example of a macro Select spreadsheet Select chart type Print sheet every time you call the macro the 3 tasks are done
automatically Some database functions are also included in some
spreadsheet programs
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Spreadsheets Spreadsheet as a modeling tool
Spreadsheet software does more than just: edit spreadsheets Perform simple calculations …
Spreadsheets allow quick data modification and result presentation
Suppose the owner of the payroll spreadsheet wants to give his/her employees a raise (in a good year)
For example the increment should be 2% for each employee a new cell in the spreadsheet to hold the fixed increment:
2% a new column headed New Pay is also needed to store the
incremented pay for each employee
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SpreadsheetsA B C D E F G
1 ID Name Age Rate Hours Pay New Pay
2 101 Janet K 51 16.60 94 1560.40 1591.61
3 102 Adam R 18 8.50 185 1572.50 1603.95
4 103 Fred L 43 12.35 250 3087.50 3149.25
5 104 John A 53 17.80 245 4361.00 4448.22
6 105 Butch H 17 6.70 53 355.10 362.20
78 Base Increase % 29 Totals $10936.50
$11155.23 G: new column for increased payC8: stores the 2% value
F9 and G9: store the total pay
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Spreadsheets Needed formulas:
D2*(1 + $C$8/100)*E2 (entered in cell G2) G3 … G6: inserted automatically (by copying) after inserting G2 same formula is used $C$ in order to prevent indexing the C column for G2 … G6
(constant value!) To compute the total in F9:
SUM(F2:F6) (entered in cell F9) this means sum up all values in cells between F2 and F6 By copying to cell G9, the corresponding formula SUM(G2:G6) is
automatically generated The nice thing is now that if the owner wants to examine an
increased pay using another percent, say 3%, only cell C8 needs to be modified!
the new column G and the total pays are adjusted automatically
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Spreadsheets The owner may also use another more realistic formula for increments:
Each employee is given a “merit” percentage over a fixed base rate
A B C D E F G H1 ID Name Age Rate Hours Pay Merit New
Pay
2 101 Janet K 51 16.60 94 1560.40 3 1638.42
3 102 Adam R 18 8.50 185 1572.50 2 1635.40
4 103 Fred L 43 12.35 250 3087.50 33241.87
5 104 John A 53 17.80 245 4361.00 2 4535.44
6 105 Butch H 17 6.70 53 355.10 1 365.75
78 Base Increase % 29 Totals $10936.50
$11416.80
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Spreadsheets Formulas needed to be typed in (for “merits” example):
First, a column (we use G) is created to model the merits Now column H is for new pay D2*(1 + ($C$8 + G2)/100)*E2 (entered in H2) Formulas in H3…H6 are generated automatically after copying
Moreover, some spreadsheet program can perform “goal seeking”
Suppose the owner only knows: What merits each employee is worth The amount of money reserved for salaries (in the current year)
Owner types in these values AND spreadsheet software seeks the amount of base increase percentage automatically
For example: Suppose amount for this year is $12000.00 Spreadsheet software will assign to cell C3 the value 7.33
automatically Owner is now happy to know what is the base increment in this
year (that does not exceed his/her expectation)
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Spreadsheets Imagine more complicated examples:
Company may vary the price of a product or the cost of supply and see immediately the effect on the profit
A chemist can experiment with the amount of additives necessary to obtain a smooth flow of a liquid in a pipe
An economist can track revenue impacts of a proposed tax increase
… spreadsheet programs have become modeling and forecasting
tools! However:
Spreadsheets can only perform “numeric” modeling Time dependence of data is not directly supported (but can be
achieved)
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Spreadsheets Programming levels of spreadsheets:
Macro programming ( highest level): Here a real programming language including (sequential, conditional,
and interactive) instruction is provided in order to develop “programs” that simplify the work (of inputting formulas etc.)
Visual programming ( intermediate level): Spreadsheet program acts like a (visual) language interpreter it waits for the user to change something, and then delivers new
results “event-driven programming” Can be compared to an (interpreted) functional language, since only
formulas (functions!) are used Formulas can:
Explicitly use if (-statement): e.g. IF(A3 > B3, A3-B3, B3-A3) Implicitly use loops: e.g. when determining a base (input) value given a
target one (like when we use target total pay 12000.00 to determine the base percentage)
Formulas (programming) ( lowest level): Use of the basic arithmetic operations: e.g. A1*B1*C1 Use of built-in functions: e.g. SUM(B2:B10), ABS(A1), etc.
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Databases Since Herman Hollerith demonstrated the advantages of mechanizing the
processing of large amounts of data (in the US census of 1890), data processing emerged and evolved to a very common task at almost each desktop computer in the world
Large amounts of data are stored in permanent storages (disks, tapes, …) Related data are organized in files in background storage:
A file has a name and further attributes, and It includes the (user) data themselves
Common file types: Text files: produced by e.g. a word processor Graphic files: produced by e.g. drawing program Program files: produced by e.g. a compiler (which is also stored in a program
file) …
File manager: Often part of the operating system
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Databases Is a program that offers operations for:
Creating a new file in a directory Reading information in a directory Updating information in a directory Deleting a file from a directory
A directory is a list of records consisting of: File name File size Time of last update Access rights …
File manager has elementary capabilities: A file is for the file manager a black box File manager cannot even distinguish file types
More than that is needed … ( data organization) But file manager is indispensable, since access to background storage is
always through it(s operations).
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Databases Data organization
Let us confine us to (simple) user data files (no program files) Data are based on bits and bytes
but these are too small quantities in real life Data can be better organized in:
Fields: a collection of bytes (e.g. employee name) Records: a collection of fields (e.g. employee information – name, phone#, …) Data files: a collection of records (e.g. all employees in a company) Database: a collection of data files (e.g. employees, inventory, …)
Structure of a database (consisting of 1 file) Field1 (e.g.ID) Field2 (e.g Name) Field3 (e.g. Age) Field4 (e.g.
PayRate)
Record1
Record2
Record3
Record4
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Database Attention: A record is unlike an array, since it may include fields of
different data types and those fields are not accessed via indexes! Database management system (DBMS)
A program that manages files in a databases Codd E. F. observed records in a file as one entity: 2-dimensional table He introduced the relational database model:
Now an employee file is not a collection of individual records but it is a 2 dimensional table
He suggested new terminology (now widely used): Entity: is what the table represents e.g. employees file Tuple: represents one instance of this entity (the old record or a row
in a table) Attribute: Heading (or name) of a column in a table (e.g. employee
name, age, …) Primary key: An attribute (or a collection of attributes) that uniquely
identifies a tuple (e.g. SSN of an employee) Relation: Same as entity from the point of view of “related”
attributes
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Databases A DBMS is more than a file manager:
It works on the level of attributes and relations It knows how data are organized and how to access them the best
(using primary keys) User data is a glass box for a DBMS (not a black box)
A DBMS is really a complex program: It has its own data definition language (DDL) It has its own data manipulation language or query language (DML)
After defining the data using DLL, the query language can be used to perform complex operations on the data
SQL: Structured Query Language Examples of queries in SQL:
Get all information about employee 123, the user poses the following query:
SELECTID, Name, Age, Payrate, Hours, PayFROM EmployeeWHERE ID = 123;
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Databases Get pays of a specific employee:
SELECT Name, PayFROM EmployeeWHERE Name = ‘John Kay’;
Get all information about employees ordered by their IDs:SELECT *FROM EmployeeORDERED BY ID;
Get all information about employees older then 21 years:SELECT *FROM EmployeeWHERE Age > 21;
A query using two tables:SELECT Employee.Name, Insurance.PanTypeFROM Employee, InsuranceWHERE Employee.Name = ‘Fred James’ AND Employee.ID =
Insurance.ID;
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Databases Issues in databases:
Transactions: All-or-nothing…
Multimedia data: Audio Video …
WWW Accessing databases using browsers
(hypermedia) Distributed Databases
Data distributed among nodes Replication and fault tolerance Security
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Numeric and Symbolic Computation
Historically, the first application of computers is numeric computation:
Baggage Analytic Engine for mathematical equations Hollerith solved statistical problems (US census 1940’s computers motivated by military-based
mathematical problems Today: numeric computation still a challenging task
Problems with up to 1015 mathematical operations are not uncommon
Typical areas: Weather forecasting Molecular analysis Real-time imaging Simulation Natural language processing
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Numeric and Symbolic Computation
Mentioned challenges yielded to the development of supercomputers and highly parallel computers
Machines with 1010 (and more) floating point operation per second have been constructed
Example: virtual reality ( real-time imaging) Computer generates images in the same time frame and with the
same orientation as when seen in real life Images are displayed on glasses and headsets are used to feel like
in a real scene For example: as you are moving your arms, legs, and eyes, the
computer may be generating and displaying simulated images of what you would see during a stroll through a forest.
High demands on computation ability: about 24 images / sec each image = e.g. one million of pixels (picture elements) for each image: hundreds or thousands of mathematical operations
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Numeric and Symbolic Computation
Computer determines repeatedly: How far you have moved (since last image) How your eyes/head is positioned What is visible (what colors etc.) and what not from the current perspective
Thus: 24 images/sec, 1000 pixels each, 1000s of operations a pixel more than 24 billion of mathematical operations per second
In another rather esoteric area: quantum chromodynamics 100 trillion (1014) of operations are needed for a single result! A regular computer (25 MIPS) would work 1.5 moths to generate result A supercomputer: 1 hour A teraflop machine: less than 2 minutes
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Numeric and Symbolic Computation
Even after the emergence of non-numeric applications (like word processing, databases, …), numeric computation are still very demanding, and in particular the field of symbolic computing
Symbolic Computing Traditional numeric problems are based on “numeric values”: e.g. 13.57/1.8897 *sin(1.2*) – cos(1.34*)*10-4
Symbolic computing works on quantities that represent numbers (like unknown variables of high school mathematics)
Examples: Spreadsheets formula: D2*E2 Simplify: -x2 + 3x – 4 + 3x2 – x + 1 Solve: x3 + 2x2 + 10x - 13 = 0 Factor: x3 + x2 – 3x – 3 Plot: sin(3x) for 0 <= x <= 2
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Numeric and Symbolic Computation There is a variety of software tools for symbolic
computation (e.g. Mathematica, Maple) Of course these tools are able to do numeric
computations as well In general the tools are interactive:
User: enters some request (here boldface) Program: displays result (here italic)
Example: N[expr, i] Entered when a numeric computation is wanted Arithmetic expression expr is evaluated with the precision I N[((13.1842/1.976) Sin[2.1 Pi])^(1.0/3.0) + 0.0406893, 6]
1.31346
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Numeric and Symbolic Computation
Most symbolic systems work with ASCII representation of numbers and not with their binary representation:
“10” = 1010 (4 bits) “10” = ‘1’’0’ (2 bytes) they can achieve high precision (but need more memory) Examples:
Compute with 250 precision: N[Pi, 250]
3.1415926535…52271201909 Compute the factorial of 200:
200! 78865786479050…737472000…00000
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Numeric and Symbolic Computation
However the strength of these systems is in symbolic computing
Examples Simplify expression: Simplify[expr]
Simplify[(x-1)^2 + (x+2) + (2x-3)^2 + x]
12 – 12 x + 5 x2
Factor polynomial: Factor[polynomial] Factor[x^10 -1]
(-1 + x) (1 + x) (1 – x + x2 - x3 + x4) (1 + x + x2 + x3 + x4) Expand expression: Expand[expr]
Expand[(1 + x + 3y)^4]
1 + 4x + 6x2 + 4x3 + x4 + 12y + 36xy + 36x2y + 12x3y + 54y2 + 108xy2 + 54x2y2 + 108y3 + 108xy3 + 81y4
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Numeric and Symbolic Computation
Solve equations: Solve[equation, unknown] Solve[x^2 – 5x + 4 == 0, x] (Note: “==“ means equal)
{{x 4} { x 1}} Solve transcendental equations like ex – 1.5 == 0
Solve[Exp[x]– 1.5 == 0, x] {{x 0.405465}
Solve system of linear equations: Solve[{2x + y == 11, 6x – 2y == 8}, {x, y}]
{{x 3, y 5}} Solve system of linear equations:
Solve[{2x + y == 11, 2x + y == 8}, {x, y}] { }
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Numeric and Symbolic Computation
Calculus operations: Differentiation:
D[x^3+6x-7, x]
6+ 3x2
Integration: Integrate[x^4 - 2, x]
1/5 x5 - 2x Summation of (convergent) infinite series:
N[Sum[1/2^i, {i, 1, Infinity}]]
1.0 Summation of (divergent) infinite series:
N[Sum[1/k, {k, 2, Infinity}]]
Sum diverges
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Numeric and Symbolic Computation Plotting functions:
Plot[x^2 + x – 2, {x, -3, +2}]
Plot[5 Sin[3x], {x, 0, 2 Pi}]
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Numeric and Symbolic Computation Various options for plots are available:
Discrete: only some points 3-dimensional: e.g. Plot3D[Sin[x*y]. {x, 0, 3}, {y, 0, 3}] …
Process of performing user requests: Get and analyze request Activate the appropriate program to handle the request Receive results Display results
Issues: Algorithms for symbolic computation Exploiting parallelism Distribution in a network
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Computer Networks A computer network consists of:
Computers Peripheral devices (printers, disks, …) An interconnection network
Types of networks: local area network: LAN e.g. within buildings Wide area network: WAN e.g. across countries
Benefits of networks: Share physical resources: e.g. one printer in a department Share logical resources: e.g. access to files, databases, … Fault tolerance: e.g. if one printer fails, another can be used Parallelism: e.g. print two documents on two different
printers Communication: e.g. email
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Computer Networks Further benefits:
Use of supercomputers in a WAN Groupware: Joint editing of documents Electronic data interchange: Data transfer from a
program to a program; e.g. orders as output from a program at company X are transmitted to another program (that handles bills and shipping) at company Y ( no human intervention)
Use of network-centric applications: WWW E-commerce Search engines …
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Computer Networks Internet
One of the largest computer networks Outgrowth of ARPANET (US DoD) ARPANET was developed in 1970s Internet is a network of networks
Advantages (of Internet) Email Voice mail Cellular phones Teleconferencing …
Issues: Reliability of networks Efficiency Privacy and confidentiality
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Computer Networks More about the Internet
Vision: “information superhighway” global information access from everywhere by
everyone at every time Information should be a basic infrastructure good Information should flow like current/voltage flows
from plugs Information is accessible through services Internet is a big WAN (actually a WAN of WANs/LANs) Internet is big collection of nodes connected by wire,
each node is either a individual computer (e.g. mainframe) or a switching station
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Computer Networks User connects to the internet using:
Workstation PC Laptop …
Connection: Direct: user connects by telephone line to a “host”
(already connected to Internet) Over LAN: user machine is in a LAN that is connected to
an internet host Internet services
Email: In order to communicate with someone via email you
must know his/her email address
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Computer Networks Addressing scheme is hierarchical: [email protected]
“jones” identifies an individual account on a host computer “ournode” identifies the host computer “ccc” identifies where the host is located (perhaps central
computer center) “uleth” identifies the organization where this machine is
located (U of L) “ca” specifies the country or organization sector (here
Canada) Problems with Email:
Is not protected (default) Informality of an email may be misinterpreted (by reader) Viruses in emails!
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Computer Networks Remote log-in
The service is called “telnet” Used to log on to any computer in the Internet Login types:
Anonymous Individual
After logging in your are like a direct user of the machines
Why? In order to access a database In order to use a special compiler In order to run a program on a supercomputer …
Clearly, the user notices a delay when accessing remote machines
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Computer Networks File transfer:
Service: FTP (file transfer protocol) This service allows a user to transfer files between two
machines Files can be of arbitrary length and of any type Commands:
Put: from your machine to remote computer Get: from remote computer to your machine …
Anonymous ftp: open services for everyone Difference between telnet, ftp, and email:
Telnet: you are a user of the remote machine FTP: you are not a user, you are only allowed to use
commands of FTP Emails: only text files, you communicate with a user (not a
machine)
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Computer Networks Browsing:
Gopher: Allows to “jump” from one machine to another collecting
information Menu-driven Menu contents e.g.
Library entries General information Next gopher site(s)
WAIS: Use keywords to retrieve information from directories in
the Internet WWW:
Hypertext-based navigation Any kind of information (text, audio, video, …) Browser software needed (e.g. Netscape, Internet
Explorer, …)
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Computer Networks Different services:
Search engines Email Applications/Applets …
Bulletin board: E.g. newsgroups: discussion groups on a specific topic Hierarchal naming e.g. cs.comp.parallel In general moderated
Chatting …
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Computer Networks Some Internet statistics (rather old)
20,000 networks in the Internet A new network every 10 minutes 4 million hosts More than 50 million people have access to the
Internet Over 5,000 news groups Over 4,000 Gopher servers Annual traffic growth of WWW is 341,634 percent!!! Internet services in use for more than 2 decades (by
insiders) Based on current growth, by 2003 every person on
the globe will have Internet access (???)
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Computer Networks Issues in networking
Transmission is analog, but data are digital conversion is needed conversion: use of Fourier series to approximate
digital signal by superposition of multiple analog ones Bandwidth: maximum transmission rate (medium-
specific) Media:
Twisted pair copper wire: Used in telephone networks Inexpensive Limited bandwidth Signal deteriorates at distances longer than 10 km (amplifiers
needed, repeaters)
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Computer Networks Coaxial cable:
Used for cable TV More bandwidth but more expensive Signal deterioration also at about 10 km but is less subject
to “noise” Fiber optic:
Bundles of thin glass wire Signal are pulses of light High bandwidth Up to 100 km without deterioration More expensive
Message transmission in a WAN In general a WAN is a switched network
messages travel from one switch to another on the way to their destinations
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Computer Networks A message includes its destination address in order to
help intermediate nodes to “switch in the right direction”
Multiple paths from source to destination are possible (and usual)
Why? Reliability: redundant connections Efficiency: more connections among nodes with
higher traffic or parallel connections What path is the best?
Shortest ones? Less intermediate nodes or less distance?
Path with highest bandwidth? Priorities for messages?
High priority messages use high bandwidth paths Low priority messages use low bandwidth paths
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Computer Networks Thus, answer is not trivial… After all, determining the “best” path is a prohibitively long
task compare: bin-packing problem O(2n) A number of routing algorithms are in use
Message transmission in a LAN Bus-based LANs (e.g. Ethernet) Broadcasting:
Any message is sent to ALL nodes in the network Each node checks whether or not it is the message destination
If yes, message is completely received and processed If not, message is ignored
Collision is possible: “A” sends “m1” and before “m1” is received “A2” sends “m2” Since medium is shared, “m2” collides with “m1” Both are then useless for potential receivers
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Computer Networks Thus, collision must be detected and sending machines
retry to send the message again In order not to collide another time the machines wait
different “random” periods before sending
