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People in a Database System Environment

People  in a Database System Environment

People component includes all users associated with the database system. On the basis of primary job function we can identify five types of users in a database system: System Administrators, Database Administrators, Data Modelers,System Analysts and Programmers and End Users.

System Administrators
Data Modelers
Database Administrators
System Analysts and Programmers
End Users

 

System Administrators oversees the database system's general operations.
 
Data Modelers (Architect) prepare the conceptualdesign from the requirement.ER model represent the conceptual design of an OLTP application.
 
Database Administrator (DBA) physically implements the database according to the logical design. The DBA performs the physical implementation and maintenance of a database system.
 
System Analysts and programmers design and implements the application programs. They create the input screens, reports, and procedures through which end users access and manipulate the database.
 

End Users are the people who use the application. For example incase of a banking system, the employees, customer using ATM or online banking facility are end users.

Software and Hardware Components in a Database System Environment

Hardware Components in a Database System Environment

Hardware identifies all the system's physical devices. It includes computers, computer peripherals, network components etc.

Software Components in a Database System Environment

Software refers to the collection of programs used with in the database system. It includes the operating system, DBMS Software, and application programs and utilities. 

Operating System
DBMS Software
Application Programs and Utilities

The operating System manages all the hardware components and makes it possible for all other software to run on the computers. UNIX, LINUX, Microsoft Windows etc are the popular operating systems used in database environment.

DBMS software manages the database with in the database system. Oracle Corporation's ORACLE, IBM's DB2, Sun's MYSQL, Microsoft's MS Access and SQL Server etc are the popular DBMS (RDBMS) software used in the database environment.

Application programs and utilities software are used to access and manipulate the data in the database and to manage the operating environment of the database.

Transaction States in DBMS

Transaction States in  transaction processing in a Database System.

 

The following are the different states in  transaction processing in a Database System.

  • Active
  • Partially Committed
  • Failed
  • Aborted
  • Committed

Active
This is the  initial state. The transaction stay in this state while it is executing.

Partially Committed
This is the  state after the final statement of the transaction is executed.

Failed
After the discovery that normal execution can no longer proceed.

Aborted
The state after the transaction has been rolled back and the database has been restored to its state prior to the start of the transaction.

Committed
The state after successful completion of the transaction.

We cannot abort or rollback a committed transaction.

 

 

Entity Relationship Model - ER Model

Entity Relationship Model (E-R Model)

The process of database design is an iterative process. The ER Model is used at the conceptual design stage of the database design.ER diagram is used to represent this conceptual design. The requirement analysis is modeled in this conceptual design. The ER model is very expressive so that people can easily understand the requirement. The data modeler prepares  the ER diagram and is verified with the functional domain experts to ensure that all the requirements are properly incorporated in the conceptual design. The process is repeated until the end users and designers agree that the E-R diagram is a fair representation of the requirement. We can easily map an ER diagram to a relational schema.

The basic constructs of  ER Model are Entity, Attributes and Relationships. An Entity is an object that exist in the real world and is distinguishable from other entities.

  • Conceptual Design
  • ER Diagram
  • Entities
  • Attributes
  • Relationships

Entities

An entity is a thing or object in the real world that is distinguishable from all other objects. For example 'Person'  in an organization is an entity. An entity has a set of properties. At the E-R modeling level an entity actually refers to an entity set. In other words, entity in ER model corresponds to a table.

  • Entity
  • Entity Set

An entity may be concrete such as a person, book etc or may be abstract such as account,loan etc. The ER model refers to a specific table row as an entity instance or entity occurrence. Collection of similar entities (Entity Set) often corresponds to a table. Each entity set has a key.All entities in an entity set have the same set of attributes. Thus entity set is a set of entities of the same type that share the same properties or attributes. An entity is represented by a rectangle containing the entity name, which is a noun usually written in capital letters.

 

Attributes

An entity is represented by a set of attributes. It corresponds to a field in a table.For each attribute there is a set of permitted values called the domain or value set of the attribute. Attributes are represented by ovals and are connected to the entity with a line. Each oval contains the name of the attribute it represents.

Relationships

A relationship describes an association among entities. In ER model the association among entities is described as one-to-one, one-to-many, many-to-many. Relationships are represented by a diamond connected to the related entities. The relationship name (an active or passive verb), is written inside the diamond.

 

Extended ER Features

Extended ER Features

  • Specialization
  • Generalization
  • Attribute Inheritance
  • Aggregation
Specialization
The process of designating sub groupings with in an entity set is called specialization.We use IS A relationship to represent specialization.IS A relationship may also be referred as super class-subclass relationship
Example: Person IS A   Employee
               Person IS A   Customer
 
             Employee IS A Manager
 
Generalization
Here the design process take place in bottom up manner.Multiple entity sets are synthesized into a higher level entity set on the basis of common features.
Example: Employee and Customer entities can be synthesized into a higher level entity Person.
 
Attribute inheritance
The attributes of higher level entity set are inherited by lower level entity set.
 
Aggregation
Aggregation is an abstraction in which relationship sets are treated as higher level entity sets. Here a relationship set is embedded inside an entity set, and these entity sets can participate in relationships.