Unit 5: The Database Architecture_Continued

The Database Architecture



B. Three-Tier Architecture
Three layers in the three-tier architecture are as below:-
1) Client layer
It is known as Presentation layer that consist of the User Interface of the application, example, is User registration form which contains text box, label, button.

2) Business layer or Application layer
All business logic is written like data validation, inserting data, etc. It acts as the intermediary layer between Client layer and Data layer.

3) Database layer
Database Access Layer/DBMS contains methods to connect with database and perform database operations like insert, update, delete, get data from database based on our input data.

Advantages
High Performance – Because the Presentation tier can cache requests, network utilization is minimized, and the load is reduced on the Application and Data tiers.
High degree of flexibility in deployment platform and configuration
Improves Security – Client do not have direct access to database
Easy to maintain and modification, will not affect other modules
More Re-use

Disadvantages
Increase Complexity.

Unit 4: The Database Architecture

The Database Architecture



Database architecture were classified into two types as below:
A. Two-Tier architecture
B. Three-Tier architecture

A. Two-Tier Architecture
The Two-tier architecture is divided into two parts:
  1-  Client (Client Tier)
  2- Database (Data Tier)

Few examples of client / server communication are:
- Communication between the desktop application to database server.
- Communication between the browser to web server.
- Communication between the FTP client to FTP server.

Advantages
1.    Easy to maintain and modification.
2.    Communication is bit faster. Requested data can be retrieved very quickly, when there is less number of users.

Disadvantages
1.   In two-tier architecture application performance of the application degrade upon increasing the number of users/load. 

It would be time consuming, when there is huge number of users. All the requests will be queued and handed one after another. Hence it will not respond to multiple users at the same time.


2.    Cost-ineffective compared to other.

Unit 3 : What are all the components of Database System?

What are all the components of Database System? 



Users: are the one who really uses the database. Users can be administrator, developer or the end users.
Tasks of users:
- Input new data
- Delete data
- Modify existing data
- Reads data.

Database Application: is the application program which helps the users to interact with the database by means of query languages. It serves as intermediary between the user and the DBMS. Its tasks includes: create/process forms, process user queries, executes application logic.

Database: is a collection of related data organized in a way that data can be easily accessed, managed and updated.
Two types of data:
1- User data: is data which is stored in the various tables of the database in the form of rows and columns.
2- Metadata: is data about data. it stores the information like how many tables and their names, how many columns and their names, primary keys, foreign keys etc.


DBMS: is the software helps the user to interact with the database. It allows the users to insert, delete, update or retrieve the data.  All these operations are handled by query languages like MySQL, Oracle etc.

Unit 6: What happens at compile time and run time?

What happens at compile time and run time?



At compile time, java file is compiled by Java Compiler (It does not interact with OS) and converts the java code into bytecode.

What happens at runtime?
- Classloader: is the subsystem of JVM that is used to load class files.
- Bytecode Verifier: checks the code fragments for illegal code that can violate access right to objects.
- Interpreter: read bytecode stream then execute the instructions.

Can we save a java source file by other name apart from class name
Yes, if the class is not public. It is explained in the figure given below:

                                       

To Compile – javac Hard.java
To execute – java Simple

Can we have multiple classes in a java source file
Yes, as shown below

Unit 5: Understanding the first Java Programming

Understanding the first Java Programming

Prerequisite – JDK – java Development Kit

class Simple
{  
public static void main(String args[])
{  
  System.out.println("Hello Java");  
  }  
}  

save this file as Simple.java
To compile: javac Simple.java
To execute: java Simple

- class keyword is used to declare a class in java.
- public keyword is an access modifier which represents visibility, it means it is visible to all.
- static is a keyword if we declare any method as static, it is known as the static method. The core advantage of the static method is that there is no need to create the object to invoke the static method. The main method is executed by the JVM, so it doesn't require to create an object to invoke the main method. So it saves memory.
- void is the return type of the method, it means it doesn't return any value.
- main represents startup of the program.
- String[] args is used for command line argument. We will learn it later.
- System.out.println() is used print statement. We will learn about the internal working off  System.out.println statement later.

Unit 2: What is Database?

What is Database?



A Database is a collection of related data organized in a way that data can be easily accessed, managed and updated.
In a database, we would be grouping only related data together and storing them under one group name called table.



For example below:
_Library catalogues 
_Medical records 
_Bank accounts 
_Product catalogues 
_Telephone directories 
_Train timetables 
_Airline bookings 
_Credit card details 
_Student records 
_Discussion boards and so on…

Databases are useful because: 
Many computing applications deal with large amounts of information 
Database systems give a set of tools for storing, searching and managing this information

Database systems are systems in which the interpretation and storage of information are of primary importance.
It is a system that allows users to Store, Update, Retrieve, Organize, and Protect their data. 

Unit 1: What is Data and Information?

What is Data and Information?



What is Data?
Data, is defined as a body of facts or figures, which have been gathered for one or more specific purposes
data can exist in the forms of
linguistic expressions (e.g. name, age, address, date, ownership)
symbolic expressions (e.g. traffic signs)
mathematical expressions (e.g. E = mc2)
signals (e.g. electromagnetic waves)

What is Information?
Information, is defined as data which have been processed into a form that is meaningful to a recipient. In other words, data has to be interpreted in order to obtain information.
- although data are ingredients of information, not all data make useful information
- information is only useful to its recipients when it is
    +  relevant (to its intended purposes and with appropriate level of required detail)
    +  reliable, accurate and verifiable (by independent means)
    +  up-to-date and timely (depending on purposes)
Information system, is  a system used to  change "data" into "information“.