18CSC303J - Database Management System UNIT 1

 12m:

DBMS System Structure. Explain


  • A primary goal of a database system is to retrieve information from database and store information into the database

  • Different types of user interfaces have been designed for the different types of users

  • There are mainly 4 types of database-system users. 


Users:

  • Naive Users: Any user who does not have any knowledge about database

  • Application Programmers: Computer Professionals who write application programs

  • Sophisticated Users: Interact with the system via requests or query language instead of writing programs

  • Database Administrator: Responsible for everything related to the database. Makes policies, strategies and provides technical support.


Query Processor Components:

  • DML Compiler: Translates DML statements into low level instructions that query evaluation engine understands

  • Embedded DML Pre-Compiler: Converts DML statements to normal procedure calls (must interact with DML compiler)

  • DDL Interpreter: Interprets the DDL statements and records them in a set of tables

  • Query Evaluation Engine: Executes low level instructions generated by the DML compiler


Storage Manager Components:( interface between the disk storage and query processor)

  • Authorization and Integrity Manager: Tests the satisfaction of integrity constraints and authority of users to access data

  • Transaction Manager: Ensures that the database remains in a consistent state despite failures

  • File manager: Manages the allocation of space on disk storage

  • Buffer Manager: Responsible for fetching data from disk storage into main memory and what to cache in memory


Disk Storage:

  • Data Files: stores the database files

  • Data Dictionary: Stores metadata about the structure of the database

  • Indices: Provides fast access to data values that holds specific values

  • Statistical Data: Stores statistical information about the data in the database


Different Types of Data Models:

  • Data Model: Basic Structure of a database

  • It is a set of tables, linked by relationships

  • 4 main categories:

  • Relational Model

  • Entity-Relationship Model

  • Object-Based Data Model

  • Semi structured Data Model


Relational Model:

  • All data must be stored in tables called relations with rows and columns

  • Relations can be normalized

  • Relationship is maintained by storing a common field


E-R Model:

  • Also called Entity relationship diagram

  • Graphical representation of entities and their relationships to each other


Object-Based Data Model:

  • Considers each entity in the world as objects and isolated it from each other

  • Based on object-oriented programming

  • Describes the state and behavior of the object


Semi structured Data Model:

  • XML language is used to represent semi structured data

  • Semi structured data is self-describing

  • It is a database model where there is no separation between the data and the schema


4m:


Database Architecture & types



2-tier DBMS Architecture:

  • Includes an application layer between the user and the DBMS

  • Responsible to send the user’s request to the DBMS and send the response of DBMS to the user


3-tier DBMS Architecture:

  • Goal is to separate each user’s view of the DBMS from the way the DBMS is physically represented

  • Application client communicates with application server to send and receive user request and response


Compare and contrast file processing system and DBMS


FILE PROCESSING SYSTEM

DBMS

Causes data redundancy

Controls data redundancy

Data cannot be shared as it is distributed

Data can be easily shared 

The cost is less than DBMS

The cost is more than FPS

Does not provide Consistency constraints

Provides different consistency constraints

Does not provide concurrency facility

Provides concurrency facility


Explain the types of attributes.

  • Simple attribute (which cannot be divided further)

  • Key attribute (uniquely identifies each entity)

  • Composite attribute (composed of many other attribute)

  • Multivalued attribute (consisting more than one value)

  • Derived attribute (derived from other attributes)


Different levels of abstraction and diagrams.

View Level:

  • Highest level of data abstraction

  • User interaction with database system

Logical Level:

  • Middle level of 3-level data abstraction 

  • What data is stored in database

Physical Level:

  • Lowest level of data abstraction

  • How data is actually stored in database


Discuss the applications of DBMS.

  • Banking (transactions)

  • Airlines (reservations, schedules)

  • Universities (registration, grades)

  • Sales (customers, products, purchases)

  • Manufacturing (production, inventory, orders, supply chain)

  • Online retailers (order tracking, customized recommendations)


How disadvantages of the file system are overcome in DBMS.

  • File systems cause data redundancy and inconsistency

  • There is a difficulty in accessing data

  • Integrity [problems cause it is hard to add new constraints or change existing ones

  • Uncontrolled concurrent accesses by multiple users can lead to inconsistencies

  • Security problems

  • Atomicity of updates

Database systems offer solutions to all the above problems.

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