Introduction to Relational Database Management System : Introduction to Relational Database Management System By Sugandha Singh Hooda (Reader, CSE) +91-9717457888 sugandha06@gmail.com
Chapter 1: Introduction : Chapter 1: Introduction Purpose of Database Systems
View of Data
Database Languages
Relational Databases
Database Design
Object-based and semi-structured databases
Data Storage and Querying
Transaction Management
Database Architecture
Database Users and Administrators
Overall Structure
Database Management System (DBMS) : Database Management System (DBMS) DBMS contains information about a particular enterprise
Collection of interrelated data
Set of programs to access the data
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
Online retailers: order tracking, customized recommendations
Manufacturing: production, inventory, orders, supply chain
Human resources: employee records, salaries, tax deductions
Databases touch all aspects of our lives
Purpose of Database Systems : Purpose of Database Systems In the early days, database applications were built directly on 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
Difficulty in accessing data
Need to write a new program to carry out each new task
Data isolation — multiple files and formats
Integrity problems
Integrity constraints (e.g. account balance > 0) become “buried” in program code rather than being stated explicitly
Hard to add new constraints or change existing ones
Purpose of Database Systems (Cont.) : Purpose of Database Systems (Cont.) Drawbacks of using file systems (cont.)
Atomicity of updates
Failures may leave database in an inconsistent state with partial updates carried out
Example: 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
Example: Two people reading a balance and updating it at the same time
Security problems
Hard to provide user access to some, but not all, data
Database systems offer solutions to all the above problems
Levels of Abstraction : Levels of Abstraction Physical level: describes how a record (e.g., customer) is stored.
Logical level: describes data stored in database, and the relationships among the data.
type customer = record
customer_id : string; customer_name : string; customer_street : string; customer_city : integer;
end;
View level: application programs hide details of data types. Views can also hide information (such as an employee’s salary) for security purposes.
View of Data : View of Data An architecture for a database system
Instances and Schemas : Instances and Schemas Similar to types and variables in programming languages
Schema – the logical structure of the database
Example: The database consists of information about a set of customers and accounts and the relationship between them)
Analogous to 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.
Data Models : Data Models A collection of tools for describing
Data
Data relationships
Data semantics
Data constraints
Relational model
Entity-Relationship data model (mainly for database design)
Object-based data models (Object-oriented and Object-relational)
Semi-structured data model (XML)
Other older models:
Network model
Hierarchical model
Data Definition Language (DDL) : Data Definition Language (DDL) Specification notation for defining the database schema
Example: 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
Specifies the storage structure and access methods used
Integrity constraints
Domain constraints
Referential integrity (references constraint in SQL)
Assertions
Authorization
Relational Model : Relational Model Example of tabular data in the relational model Attributes
A Sample Relational Database : A Sample Relational Database
SQL : SQL SQL: widely used non-procedural language
Example: 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’
Example: 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
Application programs generally access databases through one of
Language extensions to allow embedded SQL
Application program interface (e.g., ODBC/JDBC) which allow SQL queries to be sent to a database
Database Design : Database Design The process of designing the general structure of the database:
Logical Design – Deciding on the database schema. Database design requires that we find a “good” collection of relation schemas.
Business decision – What attributes should we record in the database?
Computer Science decision – What relation schemas should we have and how should the attributes be distributed among the various relation schemas?
Physical Design – Deciding on the physical layout of the database
The Entity-Relationship Model : The Entity-Relationship Model Models an enterprise as a collection of entities and relationships
Entity: a “thing” or “object” in the enterprise that is distinguishable from other objects
Described by a set of attributes
Relationship: an association among several entities
Represented diagrammatically by an entity-relationship diagram:
Object-Relational Data Models : Object-Relational Data Models Extend the relational data model by including object orientation and constructs to deal with added data types.
Allow attributes of tuples to have complex types, including non-atomic values such as nested relations.
Preserve relational foundations, in particular the declarative access to data, while extending modeling power.
Provide upward compatibility with existing relational languages.
XML: Extensible Markup Language : XML: Extensible Markup Language Defined by the WWW Consortium (W3C)
Originally intended as a document markup language not a database language
The ability to specify new tags, and to create nested tag structures made XML a great way to exchange data, not just documents
XML has become the basis for all new generation data interchange formats.
A wide variety of tools is available for parsing, browsing and querying XML documents/data
Storage Management : Storage Management 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
Issues:
Storage access
File organization
Indexing and hashing
Query Processing : Query Processing 1. Parsing and translation
2. Optimization
3. Evaluation
Query Processing (Cont.) : Query Processing (Cont.) Alternative ways of evaluating a given query
Equivalent expressions
Different algorithms for each operation
Cost difference between a good and a bad way of evaluating a query can be enormous
Need to estimate the cost of operations
Depends critically on statistical information about relations which the database must maintain
Need to estimate statistics for intermediate results to compute cost of complex expressions
Transaction Management : Transaction Management 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.
Database Architecture : Database Architecture The architecture of a database systems is greatly influenced by
the underlying computer system on which the database is running:
Centralized
Client-server
Parallel (multi-processor)
Distributed
Database Users : Database Users Users are differentiated by the way they expect to interact with
the system
Application programmers – interact with system through DML calls
Sophisticated users – form requests in a database query language
Specialized users – write specialized database applications that do not fit into the traditional data processing framework
Naïve users – invoke one of the permanent application programs that have been written previously
Examples, people accessing database over the web, bank tellers, clerical staff
Database Administrator : Database Administrator 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
Acting as liaison with users
Monitoring performance and responding to changes in requirements
Overall System Structure : Overall System Structure
End of Chapter 1 : End of Chapter 1
Figure 1.4 : Figure 1.4
Figure 1.7 : Figure 1.7