Average Case

Question 1

What is the intuition behind average case algorithms?

Answer 1

Question 2

What is the definition of Expectation of variable T?

Answer 2

Question 3

Find the expectation of T for the following:

Answer 3

Question 4

Find the expactation of the following:

Answer 4

Question 5

What is a Randomized Algorithm?

Answer 5

Question 6

What is the randomized algorithm type: Las Vegas?

What is an example of this algorithm?

Answer 6

Question 7

What is the randomised algorithm type; Monte Carlo?

Answer 7

Question 8

What are the advantages/disadvantages of randomized algorithms in general?

Answer 8

Question 9

What are the advantages/disadvantages of Las Vegas algorithms?

Answer 9

Question 10

What are the advantages/disadvantages of Monte Carlo algorithms?

Answer 10

Question 11

Why does it make more sense to think about expected time instead of worst-case time for Las Vegas algorithms?

Answer 11

Question 12

In general, how is MySQL used in PHP?

Answer 12

Question 13

What are JSPs?

For scripting languages in general, what benefits that does provide?

Answer 13

Java Server Pages (JSP):

Like PHP, JSPs consist of static elements (normally text and HTML) and JSP “Elements” that generate dynamic content.

JSPs provide:

• Language for developing text-based pages that describe how to process a request to create an HTML response
• A means of accessing server-side objects
  
  • to provide a means of generating the dynamic content using information nt directly avail to the JPS
• A mechanism for extending the JSP language
  
  • Which helps simplify repeated taskss and for future evolution of JSP technology

Which means:

• Separates the “user interface” (html) from content generation (script code)
• so we can change the page layout without changing code generating the dynamic content
  
  • easier and faster development of web applications
  • Decreased maintenance effort for web applications
    
    • hence lower cost, more reliable

Question 14

What tags enclose a Java expression that is to be evaluated for JPS?

Answer 14

The time is

Question 15

JSP support the embedding of short sequences of Java code, what do we call them?

What tags are used ot do this?

Answer 15

Called “Scriptlets”, these are embedded in HTML pages

Done with the tags (not that the ‘=’ sign is missing)

The time is:

NOTE: The declaration persists across tags

Question 16

In general how would JSP be used to access submitted form data?

Answer 16

request.getParameter(“fname”) %>

The object request is built into JSPs and refs to the HTTP request recived by the webserver from the web browser (which contains the form data).

Question 17

With JSPs and declarations, what does one need to remain mindful of?

Answer 17

Declarations are only processed once

Any declared data must be guarded to prevent invalid concurrent access

• because there are multi-threaded
• access must be synchronized

Question 18

How would you use JSPs to include another page?

Answer 18

could have body here

This is an example of using predefined tags

Question 19

What are ASPs?

Answer 19

Active Server Pages

• This is mircrosoft’s JSP “equivalent”
• Capabilities of JSPs and ASPs are very similar
• JSPs are tied to java, ASPs are more flexible
  
  • ASP.net allows any .net language

Question 20

What is required of the web server to run ASP scripts

Answer 20

An ASP-enabled web server supports the execution of server-sive ASP scripts

Such a server will invoke the ASP processory whenever a file with a .asp sufffix is encountered

• These need to be in an ASP enabled folder

Question 21

In the ASP “Programming” model, what objects are available for use in ASP scripts?

Answer 21

Question 22

At it’s most basic level what is the ASP Application object?

Answer 22

It represents the entire web application, conisisting of the various pages and associated scripts

It is initialized by the web server when the first client requests a related file

There is only a single Application object for a given application running on a server (even if there are many users)

• which of course would allow for sharing of information between clients

Question 23

What is an Application object’s physical manifestation?

Answer 23

All the .asp files in it’s corresponding [virtual] directory

• virtual directory = the directory name as viewed by the suers of the system via the web
  
  • A web server often maps from a virtual directory to a different physical directory
    
    • /images to /etc/httpd/images

Question 24

Each Application object maintains colelctions of application-level variables and objects that have been added to it.

How are they accessed?

Answer 24

Collections are essentiall object-based associative arrays

Application.Contents - contains the share variables

Application.StaticObjects - maintains the object references

Elements in collections can be manipulated by it’s position index or the associated key

• Assignment
  
  • Application.Contents.Item(“pi”) = 3.14
• Reference
  
  • pi=Application.Contents.Item(“pi”)
  • pi=Application.Contents.Item(7)
• Or using the shortcut
  
  • Application.contents(“pi”)
  • Application(“pi”)

Question 25

Application.Contents contains the shared variables, because they are shared what do we need to implement?

Answer 25

Synchronization * Application.lock * Application.unlock Note: this locks the ENTIRE contents of the collection so perfman hit can be VERY HIGH Example below:

Question 26

In HTTP the Request and the Response are actually objects. Request provides access to all the information contained in the HTTP request. The Request object maintains this information in a number of collections. What are the collections of interest to us?

Answer 26

Request.Form Request.QueryString Request.ServerVariable Request.Cookies

Question 27

What does the collection Request.Form contain? How do you access this information?

Answer 27

contains all the information about the parameters recieved via an HTTP POST request. Request.Form.Item("fname") - to get the string entered on the form in the input field with the name "fname" or, more commonly Request.Form("fname")

Question 28

What is contained in the collection Request.QueryString? How is it accessed?

Answer 28

Request.QueryString contains all the informatuon about the parameters recieved via an HTTP GET request. Accessed by: Request.QueryString("fname") or Request.QueryString.Item

Question 29

What collection does Request.ServerVariables contain? How is it accessed?

Answer 29

Contains all the information about the server's environment variablles that pertain to the current HTTP request. There's a huge list but here are the most important ones:

Question 30

What does the collection Request.Cookies contain?

Answer 30

Contains all the information about any cookies recieved from the webclient application Cookies: Are a means by which per-client information can be maintained over time - Because web servers are stateless, so the state (or data state) is stored at the client in cookies.

Question 31

In general what does the Response object allow you to do?

Answer 31

Allows your ASP script to send its response back to the web client. Allows you to control: * HTTP response message headers * HTTP response message body * when and how the response is sent

Question 32

What are the most important properties (not methods) in the Response object?

Answer 32

* Response.Buffer - wether the response is to be buffered or sent to the client as generated * useful when sending large responses such as images, sound files * Response.Expires - Content expiry time * Response.CacheControl - Cache control * Response.Cookies.Item - cookies

Question 33

What ar ethe methods defined for the Response object?

Answer 33

Question 34

What is the ObjectContext object and what does it provide?

Answer 34

Provides for "transactional execution" Transactional Execution: guarantees tha either all parts of the "transaciton" complete successfully or none of the affects of any of the parts are applied ("ACID properties") - Technically what normally happens is that completed partial-effects are undone

Question 35

What is transactional execution useful for, provide an example

Answer 35

Question 36

How does the code work for ObjectContext to ensure transactional execution?

Answer 36

To indicate the code that should be transcation is set by: In these script you explicitly test by use of: ObjectContext.SetAbort - if one fails ObjectContext.SetComplete - after the final one succeeds. You must specify code to be executed when a transaction aborts or completes OnTransactionAbort( ) OnTransactionCommit( )

Question 37

What is the Session object and what does it provide?

Answer 37

Provides a way for per-user interaction information to be stored * shopping carts as an example

Question 38

What is the Server object and what does it provide?

Answer 38

It acts as a catch-all for various additional capabilities Server.ScriptTimeout : used to limit execution time of the corresponding script * Used to prevent rougue scripe code consuming too much of a server's resources * which is a simple DNS attack It also provides the attached methods/abilities: