p. t. chung cs 649 dbms introduction to database systems p. t. chung cs 649 database management...

P. T. Chung CS 649 DBMS

Introduction to Database Systems

P. T. Chung

CS 649 Database Management Systems


Database Overview

• File Management vs Database Management

• Advantages of Database systems: storage persistence,

programming interface, transaction management

• Three level Data Model

• DBMS Architecture

• Database System Components

• Users classification


File Management Systems

• File is uninterpreted, unstructured collection of information

• File operations: delete, catalog, create, rename, open, close, read, write, find, …

• Access methods: Algorithms to implement operations along with internal file organization

• Examples: File of Customers, File of Students; Access method: implementation of a set of operations on a file of students or customers.


File Management System Problems

• Data redundancy

• Data Access: New request-new program

• Data is not isolated from the access implementation

• Format incompatible data

• Concurrent program execution on the same file

• Difficulties with security enforcement

• Integrity issues


Concurrent Program Execution

Program1

What is the final value of the account AC?

Program2

AC=AC-50

AC=AC-100

AC #103 450


Security Problems

• Allow access to the file only to the authorized personnel

• Ability to restrict access to parts of the record

• Ability to control operation usage by different users

• Protection from unauthorized use

• Protection from the derivation of unauthorized information


Data Integrity

• A database constraint is a logical constraint about the data expressed in a logical language.

– STUDENT.AGE >15

– If (STUDENT.CLASS ==cs43005) then (STUDENT.PRIOR_CLASS ==cs31001)

• Database is consistent if data at each time satisfies all integrity constraints.

• Input to any application is a set of consistent data. An application output is a set of consistent data.


Collection of Files

Hierarchical

60’s

70's

80's

90’s

now

RelationalChoice for most new

applications

Object Bases

Knowledge Bases

Network


Advantages of Databases

• Persistent Storage – Database not only provides persistent storage but also efficient access to large amounts of data

• Programming Interface – Database allows users to access and modify data using powerful query language. It provides flexibility in data management

• Transaction Management – Database supports a concurrent access to the data


Early Database Applications

• Airline Reservation Systems – Data items are: single passenger reservations; Information about flights and airports; Information about ticket prices and tickets restrictions.

• Banking Systems – Data items are accounts, customers, loans, mortgages, balances, etc. Failures are not tolerable. Concurrent access must be provided

• Corporate Records – Data items are: sales, accounts, bill of materials records, employee and their dependents


Modern Database Applications

• Client – Server architecture– DBMS serves as a server and client queries are sent to servers– Where to locate servers

• Multimedia Applications• Multidatabase Applications• Data Warehouses


Three Aspects to Studying DBMS's

1. Modeling and design of databases.

– Allows exploration of issues before committing to an implementation.

2. Programming: queries and DB operations like update.

– SQL = “intergalactic dataspeak.”

3. DBMS implementation.

.


Definitions

• A database is a collection of stored operational data used by various applications and/or users by some particular enterprise or by a set of outside authorized applications and authorized users

• A DataBase Management System (DBMS) is a software system that manages execution of users applications to access and modify database data so that the data security, data integrity, and data reliability is guaranteed for each application and each application is written with an assumption that it is the only application active in the database.


What Is Data ?

• Different view points:

– A sequence of characters stored in computer memory or storage

– Interpreted sequence of characters stored in computer memory or storage

– Interpreted set of objects


Data Levels and their Roles

• Physical – corresponds to the first view of data: How data is stored, how is it accessed, how data is modified, is data ordered, how data is allocated to computer memory and/or peripheral devices, how data items are actually represented (ASCI, EBCDIC,…)

• Conceptual – corresponds to the second view of data: What we want the data to express and what relationships between data we must express, what “ story” data tells, are all data necessary for the “story’ are discussed.

• View – corresponds to the third view of data:What part of the data is seen by a specific application


Physical Data - Example

• Physical

benjamin 63

10 3

0000035000 Jjames

6 10

3

3 6

000375 . . . . . . . . .


Examples

• Conceptual

1 TA

2 Name char(10),

2 Age char (3),

2 Salary Fixed Dec(6);

1 Student

2 Name char(10),

2 Year-of_study char(3)

2 GPA Fixed Dec(5,2);


Examples

1 STUDENTS-TA

2 Name char(25),

2 Age char (3),

2 Salary Fixed Dec(8,2),

2 Year-of_study char(3)

2 GPA Fixed Dec(3,2);

A view


Three Level Data View –Data Abstractions

View1 View k

Conceptual View Of Data

Phyisal Data Storage

. . . . .


DBMS Architecture


Logical and Physical Database Components

• Data Definition Language (DDL)• Data Manipulation Language (DML)• Host Language Interface• Data Administrator• Users• Query Processor

– Compiler– Optimizer

• Management– Transaction Manager– File Manager– Buffer Manager– Authorization and Integrity Manager

Logical

Physical


Database Languages

Faculty

Name Dept

Department

Dept Chair

SQL

SELECT Chair

FROM Faculty, DepartmentWHERE Faculty.name = “Ken Noname”

AND Faculty.Dept = Department.Dept

Data definition language (DDL) ~ like type definitions in C or C++

Data Manipulation Language (DML)Query (SELECT)UPDATE < relation name >SET <attribute> = < new-value>WHERE <condition>


Data Definition Language

• Specification notation for defining the database schema– E.g.

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

• Usually an extension of the data definition language


Data Manipulation Language

• Language for accessing and manipulating the data organized by the appropriate data model

• 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


Database Host Languages C, C++, Fortran, Lisp, COBOL

Application prog.

Local Vars

DBMSCalls to

DB

Host language is completely general

Query language—less general "non procedural" andoptimizable

(Memory)

(Storage)


Data 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


Database Users

• Naïve – do not know about database too much, invoke application programs that are prepared already

• Application Programmers – know how to interact with the system but may not know how DBMS is designed

• Sophisticated users that know advanced use of the system and can use the system and packages on the top of the system

• DBMS system users – write specialized database applications that do not fit into the traditional data processing framework


Query Processor

• Compiler – verifies whether a program or query is written in accordance with DDL and DML rules

• Optimizer – Finds the most effective way to access the required data and supply it in a user requested form. Monitors the query execution and modifies a query evaluation plan if necessary.


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.


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


File Manager

• File Manager is responsible for mapping logical database units (objects, relations, etc.) into a set of low level files.

• It is responsible for maintenance of files and indexes on them. It should be able to create and destroy index and collect unused storage space to eliminate an unneeded gaps on disks.


Buffer Manager

• Buffer Manager is responsible for the allocation and maintenance buffer space in a memory to facilitate processing database data by several concurrent applications.

• Buffer Manager decides when to load data from a buffer to a database or discard the data and under what conditions a new data should be put into a buffer


Authorization and Integrity Manager

• This manager is responsible for granting an access to database or portions thereof only to authorized users and preventing the access to unauthorized users

• Integrity manager must assure data integrity during normal database operations as well as during the database failures


The DBMS Marketplace

• Relational DBMS companies – Oracle, Sybase – are among the largest software companies in the world.

• IBM offers its relational DB2 system. With IMS, a nonrelational system, IBM is by some accounts the largest DBMS vendor in the world.

• Microsoft offers SQL-Server, plus Microsoft Access for the cheap DBMS on the desktop, answered by “lite” systems from other competitors.

• Relational companies also challenged by “object-oriented DB” companies.

• But countered with “object-relational” systems, which retain the relational core while allowing type extension as in OO systems.


Logical Data Models

• A collection of tools for describing – data – data relationships– data semantics– data constraints

• Value based models: ER Model, OO Model• Record Based Models: Relational Model


Entity-Relationship Model

• The enterprise data can be described as a set of entities and a set of relationships between them.

• Entity – a data that pertains to, or describes some component of the enterprise

• Each entity is characterized by a set of attributes

• Relationship – describes an interconnection between different entities

• Entity Set – a set of entities that are characterized by the same entity definition

• Relationship Set – a set of relationships of the same type


Entity-Relationship Model

Example of schema in the entity-relationship model


Object – Oriented Model

• An enterprise is described as a collection of objects and a collection of algorithms that work with objects

• Example: Person is an object.• Object is characterized by a set of public attributes.

Applications may refer only to public attributes; private attributes . Algorithms that implement the object may refer to private attributes; a set of protected attributes and a set of methods

• Attribute of an object can be another object• Objects are nested into a hierarchy and can inherit

attributes of their parents


Object Oriented Model

OBJECT DATA MODEL

1. Complex Objects – Nested Structure (pointers or references)

2. Encapsulation, set of Methods/Access functions3. Object Identity4. Inheritance – Defining new classes like old classes

Object model: usually find objects via explicit navigationAlso query language in some systems


Example

• Class Person{ public: Person(); ~Person(); float GetSalary(); float PutSalary(float&); string Name; int SSN; date BirthDate; private: float salary; }


Object-Oriented ModelData Encapsulation

• An object contains both data and methods to work with the data

• The physical data representation is visible only to the object creator.

• The implementation details of methods are not visible to object users

• An interface of the object consists of public attributes and methods

• Each object is characterized by an object identity


Relational Model

• An enterprise is represented as a set of relations

• Domain – is a set of atomic values. Each domain has a NULL value.

• Data type – Description of a form that domain values can be represented.

• Relation is a subset of a cartesian product of one or more domains

• The elements of relations are called tuples. Each element in the cartesian product is called attribute.


Relational model is good for:

Large amounts of data —> simple operations

Navigate among small number of relations

Difficult Applications for relational model:

• VLSI Design (CAD in general)

• CASE

• Graphical Data

CPUALU

ADDER

Adder

A

FA

ALU ADDER

Bill of Materials or transitive closure


Relational Model

• Example of tabular data in the relational modelNameStudent-id

Street City gpa

Johnson

Smith

Johnson

Jones

Smith

192-83-7465

019-28-3746

192-83-7465

321-12-3123

019-28-3746

Alma

North

Alma

Main

North

Palo Alto

Rye

Palo Alto

Harrison

Rye

3.6

2.7

3.2

4.0

3.45

Attributes

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