DBMS - Introduction.ppt

INTRODUCTION TO DATABASE MANAGEMENT
SYSTEMS
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INTRODUCTION 1

Outline
• The Need for Databases
• Data Models
• Relational Databases
• Database Design
• Storage Manager
• Query Processing
• Transaction Manager
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INTRODUCTION 2

History of Database Systems
• 1950s and early 1960s:
• Data processing using magnetic tapes for storage
• Tapes provided only sequential access
• Punched cards for input
• Late 1960s and 1970s:
• Hard disks allowed direct access to data
• Network and hierarchical data models in widespread use
• Ted Codd defines the relational data model
• Would win the ACM Turing Award for this work
• IBM Research begins System R prototype
• UC Berkeley begins Ingres prototype
• High-performance (for the era) transaction processing
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INTRODUCTION 3

History (cont.)
• 1980s:
• Research relational prototypes evolve into commercial systems
• SQL becomes industrial standard
• Parallel and distributed database systems
• Object-oriented database systems
• 1990s:
• Large decision support and data-mining applications
• Large multi-terabyte data warehouses
• Emergence of Web commerce
• Early 2000s:
• XML and XQuery standards
• Automated database administration
• Later 2000s:
• Giant data storage systems
• Google BigTable, Yahoo PNuts, Amazon, .. 9/29/2022
INTRODUCTION 4

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: 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 can be very large.
• Databases touch all aspects of our lives 9/29/2022
INTRODUCTION 5

University Database Example
• Application program examples
• Add new students, instructors, and courses
• Register students for courses, and generate class rosters
• Assign grades to students, compute grade point averages
(GPA) and generate transcripts
• In the early days, database applications were built
directly on top of file systems
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INTRODUCTION 6

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
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INTRODUCTION 7

Drawbacks of using file systems to store data (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 access needed for performance
• Uncontrolled concurrent accesses can lead to inconsistencies
• Example: Two people reading a balance (say 100) and updating it by withdrawing
money (say 50 each) 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
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INTRODUCTION 8

Levels of Abstraction
• Physical level: describes how a record (e.g., instructor) is
stored.
• Logical level: describes data stored in database, and the
relationships among the data.
type instructor = record
ID : string;
name : string;
dept_name : string;
salary : 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.
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INTRODUCTION 9

View of Data
An architecture for a database system
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INTRODUCTION 10

Instances and Schemas
• Similar to types and variables in programming languages
• Instance – the actual content of the database at a particular point in time
• Analogous to the value of a variable
• Logical Schema – the overall logical structure of the database
• Example: The database consists of information about a set of customers and
accounts in a bank and the relationship between them
 Analogous to type information of a variable in a program
• Physical schema– the overall physical structure of the database
• 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.
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INTRODUCTION 11

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)
• Semistructured data model (XML)
• Other older models:
• Network model
• Hierarchical model
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INTRODUCTION 12

Relational Model
• All the data is stored in various tables.
• Example of tabular data in the relational model Columns
Rows
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INTRODUCTION 13

A Sample Relational Database
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INTRODUCTION 14

Data Definition Language (DDL)
• Specification notation for defining the database schema
Example: create table instructor (
ID char(5),
name varchar(20),
dept_name varchar(20),
salary numeric(8,2))
• DDL compiler generates a set of table templates stored in a data dictionary
• Data dictionary contains metadata (i.e., data about data)
• Database schema
• Integrity constraints
• Primary key (ID uniquely identifies instructors)
• Authorization
• Who can access what
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INTRODUCTION 15

Data Manipulation Language (DML)
• Language for accessing and manipulating the data organized
by the appropriate data model
• DML also known as query language
• Two classes of languages
• Pure – used for proving properties about computational power and
for optimization
• Relational Algebra
• Tuple relational calculus
• Domain relational calculus
• Commercial – used in commercial systems
• SQL is the most widely used commercial language
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INTRODUCTION 16

SQL
• The most widely used commercial language
• SQL is NOT a Turing machine equivalent language
• SQL is NOT a Turing machine equivalent language
• To be able to compute complex functions SQL is usually
embedded in some higher-level language
• 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
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INTRODUCTION 17

Database Design
• 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 process of designing the general structure of the database:
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INTRODUCTION 18

Database Design (Cont.)
• Is there any problem with this relation?
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INTRODUCTION 19

Design Approaches
• Need to come up with a methodology to ensure that each
of the relations in the database is “good”
• Two ways of doing so:
• Entity Relationship Model
• Models an enterprise as a collection of entities and relationships
• Represented diagrammatically by an entity-relationship diagram:
• Normalization Theory
• Formalize what designs are bad, and test for them
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INTRODUCTION 20

Object-Relational Data Models
• Relational model: flat, “atomic” values
• 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.
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INTRODUCTION 21

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
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INTRODUCTION 22

Database Engine
• Storage manager
• Query processing
• Transaction manager
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INTRODUCTION 23

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 OS file manager
• Efficient storing, retrieving and updating of data
• Issues:
• Storage access
• File organization
• Indexing and hashing
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INTRODUCTION 24

Query Processing
1. Parsing and translation
2. Optimization
3. Evaluation
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INTRODUCTION 25

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
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INTRODUCTION 26

Transaction Management
• What if the system fails?
• What if more than one user is concurrently updating the
same data?
• 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.
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INTRODUCTION 27

Database Users and Administrators
Database
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INTRODUCTION 28

Database System Internals
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INTRODUCTION 29

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
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INTRODUCTION 30

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