Digital media technology, autumn 2007

Exercise 4, ( 1.10.-5.10.2007)

1. Company's coffee ring has about 200 employees. There is a web based information system to manage the members of the ring and their coffee consumption. The super user of the system has access on an application that may be used to change the users' status and balance information. In this application the user may specify a search by giving the initial of users' last name of a user. The search produces a list of matching employees. This list contains foe each matching employee the name and the user account name of the employee. .The user account name is used as an identifier for employees. The list is used as a menu for selecting employee records for update. An update may concern the name of the user and three integer values balance data elements. Typically the super users updates about one quarter of the user records in one session..
   Estimate the amount of data transfer and the evaluate the usability of the the following alternatives:

1. A service request is made on the server for both the search and the construction of the update form, and naturally also for the actual update. The pages are build up in the server. A new search has to be activated after each update.

     Building the menu, about 50 times: 
      request about 500B + database query 
      + result about 800B (menu and header)
      = about 1300 B
   
     Construction of the update page,  50 times
      request about 500B + database query + 
      result about 700B.
     Processing the update about 50 times
      request:  500B + database update +
      result page about 500B
     Data transfer: 50*1300 + 50*1200 + 50*1000= 175000B
     Database operations 50*menu query+ 50*user data query +50*update query
   Poor usability because of menu renewal.
   

2. Data for the list of employees matching the search condition and the numerals for the update form are fetched from the server in the Ajax way. The whole page is not renewed but only the changing parts (the menu and the update form).

   Building the menu, about 15 times (assuming that about 15 of the initials are in use):
   Apporoximaty same as in case a, some titlest etc not transfered 
      = about 1200 B
    
   Construction of the update page,  50 times:
      request about 500B + database query + 
      result about 500B (only data).
     = about 1000B
   Processing the update about 50 times
      request:  500B + database update +
      result page about 500B
   Data transfer: 15*1200B+50*1000B+50*1000B =118000B+ program code
   about 2000B= 120000B
   Database operations: 15* query for menu+50*user data +50*update 
   

3. The search condition is used to retrieve all personal data needed for the menu and the update. These are shown in a data grid..The super user is able to change the information in the grid and save the row when is has been changed.

   User group fetch 15 times:
     request 500B + database query  + result about 900B = 1400B
   Construction of the update page does not cause data transfer.
   Processing the update about 50 times
      request:  500B + database update +
      result page about 500B
   Data transfer: 15*1400B+50*1000B =21000+50000 =71000 + program
    about 6000B= 77000B
   Database operations: 15*query for user data +50*updata
   

4. There is no search possibility. All the employee records are loaded in the data grid. The update is similar to case c. User fetch 1 times: request 500B + database query + result about 1500B Construction of the update page does not cause data transfer. Processing the update about 50 times request: 500B + database update + result page about 500B Data transfer: 1*2000B+50*1000B =2000+50000 =52000 + loading the program 6000B= 58000B Database operations 1*query for users + 50*update

You may assume that there is about 100 bytes data for each employee and that name and user account occupy about 80% of this. The header information of service request and response may be assumed to be about 500 bytes each..

When data trransfer is concerned the most efficient alternative is d. It is also most efficient on database usage. A list of 200 names is quite long so choise c might be more usable.

2. Find out how data grids (of cases c and d above are typically implemented. (you need not implement one).

   Many program libraries provide a solution for this. When the record in clicked its fields turn to editable and 'save' and 'reset' buttons appear. There are many ways to implement this, for example a ready made hidden form.

3. A simple example of loading a file using Ajax technique was shown in lectures. Improve the example so that text files pertain their original lines and the whole contents of xml-files are shown.. Copy the files in folder http://www.cs.helsinki.fi/u/laine/dime/s07/aesim/. The example file is in Finnish. The first menu option is the Javascript source for the loader function (you should change this), the second one is the css-file, third is an xhtml file and the last one is an xml file.

   http://www.cs.helsinki.fi/u/laine/dime/s07/ajax2.html shows one answer.

4. Construct a small page that when loaded checks if Javascript and cookies are allowed and informs at least when they are not allowed.

   See page http://www.cs.helsinki.fi/u/laine/dime/s07/cookitest.html

Exercise to be done during exercise session: Build a skeleton for a php-page on the department's : php-server. The page should show a title, the date and a text you provide as a parameter.. Instructions in Finnish