ANSWER :

6.1 Using JOIN to Retrieve Data:

When we follow the rules of database normalization and have data separated into multiple tables, linked together using primary and foreign keys, we need to be able to build a SELECT that reassembles the data across the tables. SQL uses the JOIN clause to reconnect these tables. In the JOIN clause you specify the fields that are used to reconnect the rows between the tables.

Consider the following program which creates two tables tblStudent and tblMarks as discussed in the previous section. Few records are inserted into both the tables. Then we extract the marks of students who are studying in 6^th semester.

The query joins two tables and extracts the records where RollNo and sem matches in both the tables, and sem must be 6.

ANSWER :

In the previous Question 1, we retrieved the text data from the webpage. Similar logic can be used to extract images on the webpage using HTTP. In the following program, we extract the image data in the chunks of 5120 bytes at a time, store that data in a string, trim off the headers and then store the image file on the disk.

When we run the above program, the amount of data (in bytes) retrieved from the internet is displayed in a cumulative format. At the end, the image file 'stuff.jpg' will be stored in the current working directory. (One has to verify it by looking at current working directory of the program).

ANSWER :

Refer 4^th Question & Answer (With Program if provided) or Click Here

ANSWER :

ANSWER :

9.1 Application Programming Interface (API) / Service-Oriented Architecture (SOA)

Application Programming Interface defines and documents the contracts between the applications. When we use an API, generally one program makes a set of services available for use by other applications and publishes the APIs (i.e., the "rules") that must be followed to access the services provided by the program.

When we begin to build our programs where the functionality of our program includes access to services provided by other programs, we call the approach a

Service-Oriented

Architecture

(SOA). A SOA approach is one where our overall application makes use of the services of other applications. A non-SOA approach is where the application is a single stand-alone application which contains all of the code necessary to implement the application.

Consider an example of SOA: Through a single website, we can book flight tickets and hotels. The data related to hotels is not stored in the airline servers. Instead, airline servers contact the services on hotel servers and retrieve the data from there and present it to the user. When the user agrees to make a hotel reservation using the airline site, the airline site uses another web service on the hotel systems to actually make the reservation. Similarly, to reach airport, we may book a cab through a cab rental service. And when it comes time to charge your credit card for the whole transaction, still other computers become involved in the process. This process is depicted in Figure 9.1.

Fig 9.1 Service-oriented architecture

SOA has following major advantages:

i. we always maintain only one copy of data (this is particularly important for things like hotel reservations where we do not want to over-commit)

ii. the owners of the data can set the rules about the use of their data.

With these advantages, an SOA system must be carefully designed to have good performance and meet the user's needs. When an application makes a set of services in its API available over the web, then it is called as

web services.