Database Management System PDF

68241102 9/15/2024 Database Management System Dr. Parul Saxena Program: MCA Department of CSE MITS, Gwalior 1 Course outcomes: Student would be able to  CO1:Differentiate database systems from file...

68241102 9/15/2024 Database Management System Dr. Parul Saxena Program: MCA Department of CSE MITS, Gwalior 1 Course outcomes: Student would be able to  CO1:Differentiate database systems from file 9/15/2024 systems by enumerating the features provided by database systems  CO2:Define the terminology, features, classifications, and characteristics embodied in database systems.  CO3:Design principles for logical design of databases, including the E‐R method and normalization approach.  CO4:Evaluate database storage structures and access techniques  CO5:Identify the issues of transaction processing and concurrency control.  CO6:Analyze an information storage problem and derive an information model expressed in the form of an entity relation diagram and other optional analysis forms, such as a data dictionary. 2 CHAPTER 1: INTRODUCTION Purpose of Database Systems 9/15/2024   View of Data  Data Definition Language  Data Manipulation Language  Transaction Management  Storage Management  Database Administrator  Database Users  Overall System Structure 3  DATABASE MANAGEMENT SYSTEM (DBMS) 9/15/2024  Collection of interrelated data  Set of programs to access the data  DBMS contains information about a particular enterprise or business or project.  DBMS provides an environment that is both convenient and efficient to use.  Database Applications:  Banking: all transactions  Airlines: reservations, schedules  Universities: registration, grades  Sales: customers, products, purchases  Manufacturing: production, inventory, orders, supply chain  Human resources: employee records, salaries, tax deductions  Databases touch all aspects of our lives 4 PURPOSE OF DATABASE SYSTEM  In the early days, database applications were built on 9/15/2024 top of file systems  Drawbacks of using file systems to store data:  Data redundancy and inconsistency  Multiple file formats, duplication of information in different files  data redundancy can cause data inconsistency, which can provide a company with unreliable and/or meaningless information.  Difficulty in accessing data  Need to write a new program to carry out each new task  Data isolation — multiple files and formats  One of the goals of isolation is to allow multiple transactions to occur at the same time without adversely affecting the execution of each other.  Integrity problems  Integrity constraints (e.g. account balance > 0) become part of program code  Hard to add new constraints or change existing ones 5  PURPOSE OF DATABASE SYSTEMS (CONT.)  Drawbacks of using file systems (cont.) 9/15/2024  Atomicity of updates  Failures may leave database in an inconsistent state with partial updates carried out  E.g. transfer of funds from one account to another should either complete or not happen at all  Concurrent access by multiple users  Concurrent accessed needed for performance  Uncontrolled concurrent accesses can lead to inconsistencies  E.g. two people reading a balance and updating it at the same time  Security problems  Database systems offer solutions to all the above problems 6 LEVELS OF ABSTRACTION 9/15/2024  Physical level describes how a record (e.g., customer) is stored.  Logical level: describes data stored in database, and the relationships among the data. Structure and constraints for the entire database. type customer = record name : string; street : string; city : integer; end;  View level: application programs hide details of data types. Views can also hide information (e.g., salary) for security purposes. 7  VIEW OF DATA An architecture for a database system 9/15/2024 8 INSTANCES AND SCHEMAS  Similar to types and variables in programming languages  Schema – the logical structure of the database  e.g., the database consists of information about a set of customers and 9/15/2024 accounts and the relationship between them  Type information of a variable in a program  Physical schema: database design at the physical level  Logical schema: database design at the logical level  Instance – the actual content of the database at a particular point in time  Analogous to the value of a variable  Physical Data Independence – the ability to modify the physical schema without changing the logical schema  Applications depend on the logical schema  In general, the interfaces between the various levels and components should be well defined so that changes in some parts do not seriously influence others.  Change of Location of Database from say C drive to D Drive  Using a new storage device like Hard Drive or Magnetic Tapes  Logical Data Independence - Logical Data Independence is mainly concerned with the structure or changing the data definition. 9  Add/Modify/Delete a new attribute, entity or relationship is possible without a rewrite of existing application programs Logical Data Independence Physical Data Independence Logical Data Independence is mainly Mainly concerned with the storage of the concerned with the structure or changing data. the data definition. 9/15/2024 It is difficult as the retrieving of data is It is easy to retrieve. mainly dependent on the logical structure of data. You need to make changes in the A change in the physical level usually Application program if new fields are does not need change at the Application added or deleted from the database. program level. Modification at the logical levels is Modifications made at the internal levels significant whenever the logical may or may not be needed to improve the structures of the database are changed. performance of the structure. Concerned with conceptual schema Concerned with internal schema Example: Add/Modify/Delete a new Example: change in compression attribute techniques, storage devices etc. 10 DATA DEFINITION LANGUAGE (DDL)  Specification notation for defining the database 9/15/2024 schema.  E.g. CREATE, DROP, ALTER, RENAME create table account ( account-number char(10), balance integer)  DDL compiler generates a set of tables stored in a data dictionary.  Data dictionary contains metadata (i.e., data about data).  database schema  Data storage and definition language  language in which the storage structure and access methods used by the database system are specified 11  Usually an extension of the data definition language A SAMPLE RELATIONAL DATABASE 9/15/2024 12 DATA MANIPULATION LANGUAGE (DML) 9/15/2024  Language for accessing and manipulating the data organized by the appropriate data model  DML also known as query language  Two classes of languages  Procedural – user specifies what data is required and how to get those data  Nonprocedural – user specifies what data is required without specifying how to get those data  SQL is the most widely used query language 13 SQL  SQL: widely used non-procedural language 9/15/2024  E.g. find the name of the customer with customer-id 192-83-7465 select customer.customer-name from customer where customer.customer-id = ‘192-83-7465’  E.g. find the balances of all accounts held by the customer with customer-id 192-83-7465 select account.balance from depositor, account where depositor.customer-id = ‘192-83-7465’ and depositor.account-number = account.account- number 14 DATABASE USERS  Users are differentiated by the way they expect to interact with the system 9/15/2024  Application programmers – interact with system through DML calls. They are the back end programmers who writes the code for the application programs.  Sophisticated users – form requests in a database query language. They are engineers, scientists, business analyst, who are familiar with the database. They can develop their own database applications according to their requirement.  Naive users – invoke one of the permanent application programs that have been written previously  E.g. people accessing database over the web, bank tellers, clerical staff. They don’t have any DBMS knowledge but they still use the 15 database and perform their given task. DATABASE ADMINISTRATOR 9/15/2024  Coordinates all the activities of the database system; the database administrator has a good understanding of the enterprise’s information resources and needs.  Database administrator's duties include:  Schema definition  Storage structure and access method definition  Schema and physical organization modification  Granting user authority to access the database  Specifying integrity constraints  Monitoring performance and responding to changes in requirements 16 TRANSACTION MANAGEMENT 9/15/2024  A transaction is a collection of operations that performs a single logical function in a database application  Transaction-management component ensures that the database remains in a consistent (correct) state despite system failures (e.g., power failures and operating system crashes) and transaction failures.  Concurrency-control manager controls the interaction among the concurrent transactions, to ensure the consistency of the database. 17 STORAGE MANAGEMENT 9/15/2024  Storage manager is a program module that provides the interface between the low-level data stored in the database and the application programs and queries submitted to the system.  The storage manager is responsible to the following tasks:  interaction with the file manager  efficient storing, retrieving and updating of data 18 SYSTEM STRUCTURE 9/15/2024 19 DATA MODELS A collection of tools for describing 9/15/2024   data  data relationships  data semantics  data constraints  Entity-Relationship model  Relational model  Other models:  object-oriented model  Older models: network model and hierarchical model 20 ENTITY RELATIONSHIP MODEL (CONT.) 9/15/2024  E-R model of real world  Entities (objects)  E.g. customers, accounts, bank branch  Relationships between entities  E.g. Account A-101 is held by customer Johnson  Relationship set depositor associates customers with accounts  Widely used for database design  Database design in E-R model usually converted to design in the relational model which is used for storage and processing 21 ENTITY-RELATIONSHIP MODEL 9/15/2024 Example of schema in the entity-relationship model 22 RELATIONAL MODEL Attributes  Example of tabular data in the relational model 9/15/2024 Customer- customer- customer- customer- account- id name street city number 192-83-7465 Johnson Alma Palo Alto A-101 019-28-3746 Smith North Rye A-215 192-83-7465 Johnson Alma Palo Alto A-201 321-12-3123 Jones Main Harrison A-217 019-28-3746 Smith North Rye A-201 23 DBMS SCHEMA 9/15/2024  Definition of schema: Design of a database is called the schema. Schema is of three types: Physical schema, logical schema and view schema.  For example: We have a schema that shows the relationship between three tables: Course, Student and Section. The diagram only shows the design of the database, it doesn’t show the data present in those tables. Schema is only a structural view(design) of a database. 24  The design of a database at physical level is called physical schema, how the data stored in blocks of storage is described at this level. 9/15/2024  Design of database at logical level is called logical schema, programmers and database administrators work at this level, at this level data can be described as certain types of data records gets stored in data structures, however the internal details such as implementation of data structure is hidden at this level (available at physical level).  Design of database at view level is called view schema. This generally describes end user interaction with database systems. 25 DBMS INSTANCE  Definition of instance: The data stored in database at a particular moment of time is called instance of 9/15/2024 database. Database schema defines the variable declarations in tables that belong to a particular database; the value of these variables at a moment of time is called the instance of that database.  For example, lets say we have a single table student in the database, today the table has 100 records, so today the instance of the database has 100 records. Lets say we are going to add another 100 records in this table by tomorrow so the instance of database tomorrow will have 200 records in table. In short, at a particular moment the data stored in database is called the instance, that changes over time when we add or delete data from the database. 26