unit -1 basics of DBMS, Summaries of Database Management Systems (DBMS)

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Database Management System

Unit- 1

Ch. Swathi,

Asst. Professor, CSE

Introduction

to database

• Database
  • collection of interrelated data in an organized

manner.

• Database Management system (DBMS)
  • Set of programs to access database.
• Primary goal of DBMS:
  • convenient and efficient way to store and retrieve.
• DBMS must ensure safety of information from system crashes or unauthorized access.

Purpose of Database Systems File system Vs DBMS ❖ Data redundancy - same information may be duplicated in several files. ❖ Data inconsistency – changes may not reflect every where data is redundant,. ❖ Difficulty in accessing data – difficulty in retrieving data in a convenient and efficient manner. ❖ Data isolation – Data scattered in various files and in different formats. Difficult to retrieve appropriate data. ❖ Data integrity problems – difficulty to maintain consistency constraints. ❖ Atomicity problems – difficult to ensure atomicity in file system. ❖ Concurrent access anomalies – chances of data inconsistency when multiple people access same data. ❖ Security – any user can access all data. ❖ Standards – no standard maintained in file system.

View of Data

• Major purpose of DBMS is to provide users with an abstract view of the data
• Data abstraction
  • Physical level – describes how data are stored
  • Logical level – describes what data are stored
  • View level – describes only part of data.
  • Example: Employee = ID : char(5), name : char(20), dept_name : char(20), salary : numeric(8,2); Dept = dept_no : int, dept_name : char(20), dept_head : char(5);

Data Models

❖Collection of conceptual tools for describing data, data relationships, data semantics, and consistency constraints. ❖ Relational model - collection of tables represents both data and relationships ❖ Entity – Relationship model – collection of real time objects called ‘entities’ and relationships among these entities. ❖ Semi-structured data model – Individual data items with different sets of attributes. E.g. XML ❖ Network and Hierarchical data models.

Database Languages

❖ Data Manipulation Language – insert, update, retrieve and deletion of data.

• Procedural – specify what data are needed and how to get those data
• Non-procedural - specify what data are needed without specifying how to get those data. ▪ A query is a statement requesting the retrieval of information. ▪ The portion of a DML that involves information retrieval is called a query language.

Relational Databases

❖A relation database is based on the relational model and uses a collection of tables to represent both data and the relationships among those data. ❖Collection of tables and relationship among the tables. ❖Uses DDL and DML to create tables and maintain data. ❖Supports Database Access from Application Programs.

Data Storage and Querying

❖The functional components of a database system

▪ storage manager and query processor.

❖ Storage manager – interface between the database and the application

programs and queries submitted to the system.

▪ the storage manager is responsible for storing, retrieving, and updating

data in the database.

▪ The storage manager components include:

✓ Authorization and integrity manager ✓ Transaction manager – ensures that the database remains in a consistent (correct) state concurrent transaction executions proceed without conflicting. ✓ File manager – manages the allocation of space on disk storage and the data structures used to represent information stored on disk. ✓ Buffer manager – fetches data from disk storage into main memory, and decides what data to cache in main memory. contd..

Transaction Management

❖A transaction is a collection of operations that performs a single logical function in a database application. ❖A transaction must keeps the database: ✓ Atomic ✓ Consistent ✓ Durable ❖The transaction manager consists of the concurrency-control manager and the recovery manager. ✓concurrency-control manager to control the interaction among the concurrent transactions, to ensure the consistency of the database. ✓Ensuring the atomicity and durability properties is the responsibility of the recovery manager.

Database Architecture

❖ The architecture of a database system is greatly influenced by the underlying computer system on which the database system runs.

Database Users

❖ Naive Users - unsophisticated users who interact with the system through form interface. ❖ Application Programmers – professionals who write application programs. ❖ Sophisticated Users - interact with the system by writing queries. ❖ Specialized Users - more than sophisticated users deals with complex databases. ❖ Database Administrators - A person who has central control over the system. ✓Schema definition. ✓Storage structure and access-method definition. ✓Schema and physical-organization modification. ✓Granting of authorization for data access. ✓Routine maintenance. ▪ Periodic backup ▪ Enough free disk space ▪ Performance enhancement

Summary

❖A database-management system (DBMS) consists of a collection of interrelated data and a collection of programs to access that data. The data describe one particular enterprise. ❖The primary goal of a DBMS is to provide an environment that is both convenient and efficient for people to use in retrieving and storing information. ❖Database systems management involves both the definition of structures for the storage of information and the provision of mechanisms for the manipulation of information. In addition, the database system must provide for the safety of the information stored, in the face of system crashes or attempts at unauthorized access. ❖A major purpose of a database system is to provide users with an abstract view of the data. That is, the system hides certain details of how the data are stored and maintained. ❖Underlying the structure of a database is the data model: a collection of conceptual tools for describing data, data relationships, data semantics, and data constraints. ❖The relational data model is the most widely deployed model for storing data in databases. Other data models are the object-oriented model, and semi-structured data models.

Summary

❖The architecture of a database system is greatly influenced by the underlying computer system on which the database system runs. ❖Database applications are typically broken up into a front-end part that runs at client machines and a part that runs at the back end. ▪ In two-tier architectures, the front end directly communicates with a database running at the back end. ▪ In three-tier architectures, the back end part is itself broken up into an application server and a database server. ❖There are four different types of database-system users, differentiated by the way they expect to interact with the system. Different types of user interfaces have been designed for the different types of users.

Database Design

• Conceptual design : (ER Model is used at this stage.)
  • What are the entities and relationships in the enterprise?
  • What information about these entities and relationships should we store in the database?
  • What are the integrity constraints or business rules that hold?
  • A database `schema’ in the ER Model can be represented pictorially (ER diagrams).
  • Can map an ER diagram into a relational schema.