christoph f. eick introduction file and database systems first 4 weeks 1. introduction to databases...

Christoph F. Eick Introduction File and Database Systems

First 4 Weeks

1. Introduction to Databases2. Course Information 3. Grading and Other Things4. Questionnaire5. The Relational Data Model6. Relational Algebra / SQL Part17. The E/R Data Model 8. SQL Part2

Week1/2

Weeks 2-4

Christoph F. Eick Introduction File and Database SystemsTextbooks for COSC 6340

Required Text: Raghu Ramakrishnan and Johannes Gehrke, Data Management Systems, McGraw Hill, Third Edition, 2002

Other books with relevant material: Ramez Elmasri and Shamkant Navathe, Fundamentals of Database Systems, Fourth Edition


Lectures in COSC 34801. Basic Concepts of Database Management (2-3 classes; Chapter 1, 2.1,2.2, 2.3;

instructor teaching material) 2. Introduction to the Relational Data Model (1.5 classes; Chapter 3.1, 3.2, 3.3, 3.4, 3.6)3. Introduction to the Relational Algebra and SQL (3-4 classes; Chapter 4.2, Chapter 5)4. Conceptual Schema Design using the Entity Relationship Data Model (2-3 classes;

instructor material; Chapters 2.4, 2.5) 5. Relational Database Design and Normalization (2-3 classes; instructor material,

Chapter 19) 6. Introduction to KDD and Data Warehousing (2 classes; instructor material, Chapters

25 and 26) 7. Disks, Files, Storage Structures, Index Structures and Physical Database Design (4

classes, Chapter 8, 9, 10, 11.1, 11.2, 13, 20) 8. Internet Databases and XML (1-2 classes; Chapter 7 and 27) 9. Query Optimization (1 class; Chapter 12, only if enough time left)10. Summary: Where Do We Stand? (1 class; instructor material)


Databases

Definition: A database is a collection of data with the following properties:

It represents certain aspect of the real-world. Its data are logically related. It is created for a specific purpose.


Definition: A database management system (DBMS) is a set of software that are used to define, store, manipulate and control the data in a database.

define --- define data types, structures and constraints. store --- store data; provide efficient access. manipulate --- perform retrieval and update operations using a

query language. control --- control access to data.

Database System = Database + DBMS

DBMS


A Brief History Note

Database technology has a history of about 40 years. Database technology has gone through several generations .

First Generation: File systems, 50's -- 60's A typical file system consists of a set of independent files, and

a number of application programs

Definition: A file stores a set of record (on a disk drive) all of

which have the same format.


An Example File System

A banking system may have

files for customers, saving accounts and checking

accounts;

application programs to deposit and withdraw money, to

find balance, etc.

different files are used for customers, saving and checking

accounts


Problems of File Systems (1)

It is difficult to support new applications. Two existing

application programs:

(i) find customers who have a checking account

(ii) find customers who have a saving account Need a new program to find the customers who have a

checking account and a saving account.



It has no centralized control of all data. Files are often created for a particular application. Files are created and managed independently.



There often exists severe data redundancy and inconsistency.

Checking-Account: Acct#, Owner-name, Owner-SSN, Owner-Addr, Balance, ...

Saving-Account: Acct#, Owner-name, Owner-SSN, Owner-Addr, Balance, Interest, …



It lacks concurrency control.

Concurrency control: prevent mutual interference of concurrent requests.

Example (Airplane ticket reservation): Consider the situation

when two customers are trying to book the only ticket left

for a flight through two operators at about the same time.



Weak security

Can not provide multiple views of the same data Lack isolation between program and data

Lack self-describing feature


Database History (Continued)

Second Generation: Hierarchical database systems (HDBS),

late 60's -- early 70's Best known HDBS: IMS (Information Management System

of IBM). One-to-many relationships between parent records and

child records which can have different types. Data are organized in trees Records are connected by pointers.


An IMS Query

Query: find all Binghamton University students whose major is computer science and whose GPA is higher than 3.5.

GU University (Name = `Binghamton University')

Department (Name = `Computer Science')

Student (GPA > 3.5)

L1: GNP Student (GPA > 3.5)

Goto L1


History of Database (Continued)

Third Generation: Network database systems (NDBS), late 60's -- early 70's

Some commercial NDBSs: IDS II (Honeywell), DMS II

(UNISYS). In NDBS, record types are organized into an acyclic graph.

Main problem with HDBS and NDBS: difficult to use.



Fourth Generation: Relational database systems (RDBS), early 70's -- now

Example relational DBSs: Oracle 7, Sybase, Informax, DB2, Ingres, ...

In RDBS, data are organized into tables (relations).



Fifth Generation: Object-oriented and Object-Relational database systems (OODBS), 80's -- now

Example OODBSs: O2, Objectivity, ObjectStore, Versant, … Example ORDBSs: Oracle 8, Informix, UniSQL/X.


Database Languages

Data Definition Language (DDL): used by DBA or database designer to define database schemas.

Data Manipulation Language (DML): used by database users to retrieve, insert, delete and update data in the database.Query language: The part of DML that is used to retrieve data.

Data Control Language (DCL): used by database owners and DBA to control the access of data.


Persons Involving DBS (1)

DBMS developers: Those who design and implement

DBMS software: buffer manager, query processor,

transaction manager, interface, ... Database designers: Those who are responsible for

determining

what data should be stored in the database;how data in the database should be organized; the design of customized views; the design of special data structures to improve

the performance of the system.



Database administrator (DBA): Those who manage and monitor the daily operation of a database system.

authorization for database access, e.g., who can access what data in what mode.

routine maintenance: backup, install new tools, ...modification to existing database design.



End-users:

Casual users: those who access the database using SQL directly.

Naive users: those who access the database using pre-prepared packages.

Application programmers: Those who write menu applications for naive users, typically, through database calls embedded in a program.


After This Course, You Will Be

familiar with the relational data model; a decent database designer; a sophisticated casual user; a good application programmer; knowledgeable with major aspects on how to use a DBMS knowledge in a few advanced topics with respect to

database systems This course will not teach you to become a database

administrator


Popular Topics in Databases Efficient algorithms for data collections that reside on disks (or

which are distributed over multiple disk drives, multiple computers or over the internet).

Study of data models (knowledge representation, mappings, theoretical properties)

Algorithms to run a large number of transactions on a database in parallel; finding efficient implementation for queries that access large databases; database backup and recovery,…

Database design How to use database management systems as an application

programmer / end user. How to use database management systems as database

administrator How to implement database management systems Data summarization, knowledge discovery, and data mining Special purpose databases (genomic, geographical, internet,…)


Review: Why are integrated databases popular?

IntegratedDatabase

BookkeepingDevice

Car Salesman


Review: Why are integrated databases popular?

Avoidance of uncontrolled redundancy Making knowledge accessible that would otherwise not be

accessible Standardization --- uniform representation of data facilitating

import and export Reduction of software development (though the availability of

data management systems) Support for Parallel Access and Data Security

IntegratedDatabase

BookkeepingDevice

Car Salesman


Data Model

Data Model

Schema (definesa set of database

states)

Current Database State

is used to define


Schema for the Library Example using the E/R Data Model

Many-to-Many1-to-1 1-to Many Many-to-1

title

authorB#

when

phone

name

ssn

Check_out Person Book(0,35) (0,1)


Relational Schema for Library Example in SQL/92

CREATE TABLE Book (B# INTEGER, title CHAR(30), author CHAR(20), PRIMARY KEY (B#));

CREATE TABLE Person (ssn CHAR(9), name CHAR(30), phone INTEGER, PRIMARY KEY (ssn));

CREATE TABLE Checkout( book INTEGER, person CHAR(9), since DATE, PRIMARY KEY (book), FOREIGN KEY (book) REFERENCES Book, FOREIGN KEY (person) REFERENCES Person));


Example Instances

Person(name, ssn, phone): (Eick,111111111.33345), (Miller, 222222222,33337)

Book(B#,title, author): (1,Today,Yu), (2, Today, Yu), (7, Blue, Xu)

Checkout(book,person,since): (2,222222222.8/8/05), (7,222222222,8/8/05)


Referential Integrity in SQL/92

SQL/92 supports all 4 options on deletes and updates. Default is NO ACTION

(delete/update is rejected) CASCADE (also delete all tuples

that refer to deleted tuple) SET NULL / SET DEFAULT (sets

foreign key value of referencing tuple)

CREATE TABLE Enrolled (sid CHAR(20), cid CHAR(20), grade CHAR(2), PRIMARY KEY (sid,cid), FOREIGN KEY (sid) REFERENCES Students

ON DELETE CASCADEON UPDATE SET DEFAULT )


Example of an Internal Schemafor the Library Example

INTERNAL Schema Library12 references Library. Book is stored sequentially, index on B# using hashing, index on Author using hashing. Person is stored using hashing on ssn. Check_out is stored sequentially, index on since using B+-tree.


Example: Stored Database

Relation Book

(11, Y,W)(30, Z, B)

(20, Y,W)(51, C, B)

(1, C,W)

11151

Index on B#Block#= B# mod 10

0

1

2030

(101,…)Relation PersonBlock#= sss mod 10

0

1

(200,…)(500,…)

W,…

Index on Author

RelationCheckout

Index on since


3 Schema Architecture

ExternalSchema

ExternalSchema

External Schema

ConceptualSchema

Internal Schema

How usersSee the Data

What the databasecontains and whatconstraints hold withrespect to the database

How the data arephysically stored


Data Independence

Data Independence: the ability to modify the lower level descriptions of a database without causing application programs to be rewritten.

Logical Data Independence: the ability to modify the conceptual schema without causing application programs to be rewritten.

Physical Data Independence: the ability to modify the internal schema without causing application programs to be rewritten.

Data independence is achieved through proper manipulation of the

above two mappings.

Modern Relational DBMSModern Relational DBMS

Modern DBMS

Modern DBMS

Support for Web-Interfaces, XML, andData Exchange

Efficient Implementation of Queries (Query Optimization, Join & Selection & Indexing techniques)

Transaction Concepts; capability

of running manytransactions in

parallel; support forbackup and recovery.

Support for specialData-types: long fields,images, html-links, DNA-sequences,spatial information,…

Support for higher level user interfaces:graphical, natural language, form-based,…

Support for OLAP and Data Warehousing

Support for Data Mining

operations

Support for OO; capability to store operations

Supportfor data-driven computing


Disks and Files

DBMS stores information on (“hard”) disks. This has major implications for DBMS design!

READ: transfer data from disk to main memory (RAM). WRITE: transfer data from RAM to disk. Both are high-cost operations, relative to in-memory

operations, so must be planned carefully!


Remark: All reported disk performance/prize data are as of middle of 2003

Why Not Store Everything in Main Memory?

Costs too much. $100 will buy you either 512MB of RAM or 50GB of disk today --- that is disk storage 100 times cheaper (but it is approx. 10000 times slower).

Main memory is volatile. We want data to be saved between runs. (Obviously!)

Typical storage hierarchy: Main memory (RAM) for currently used data. Disk for the main database (secondary storage). Tapes for archiving older versions of the data

(tertiary storage).

Components of a Disk

Platters

The platters spin (say, 90rps).

Spindle

The arm assembly is moved in or out to position a head on a desired track. Tracks under heads make a cylinder (imaginary!).

Disk head

Arm movement

Arm assembly

Only one head reads/writes at any one time.

Tracks

Sector

Block size is a multiple of sector size (which is fixed).


Accessing a Disk Page

Time to access (read/write) a disk block: seek time (moving arms to position disk head on

track) rotational delay (waiting for block to rotate under

head) transfer time (actually moving data to/from disk

surface) Seek time and rotational delay dominate.

Seek time varies from about 1 to 20msec Rotational delay varies from 0 to 10msec Transfer rate is about 1msec per 32KB page


Support for Transactions

Database management systems provide powerful transaction concepts that “guarantee” ACID properties

Transaction:

Begin_Transaction

<set of operations that read and modify the database>

End_Transaction Usually 2 commands are available to terminate a transaction:

Abort and Commit


Review: The ACID properties

AA tomicity: All actions in the Xact happen, or none happen. CC onsistency: If each Xact is consistent, and the DB starts

consistent, it ends up consistent. II solation: Execution of one Xact is isolated from that of

other Xacts. D D urability: If a Xact commits, its effects persist.

The Recovery Manager guarantees Atomicity & Durability.


Example

Consider two transactions (Xacts):

T1: BEGIN A=A+100, B=B-100 ENDT2: BEGIN A=1.06*A, B=1.06*B END

Intuitively, the first transaction is transferring $100 from B’s account to A’s account. The second is crediting both accounts with a 6% interest payment.

There is no guarantee that T1 will execute before T2 or vice-versa, if both are submitted together. However, the net effect must be equivalent to these two transactions running serially in some order.


Atomicity of Transactions

A transaction might commit after completing all its actions, or it could abort (or be aborted by the DBMS) after executing some actions.

A very important property guaranteed by the DBMS for all transactions is that they are atomic.

DBMS logs all actions so that it can undo the actions of aborted transactions and redo the actions of successful transactions.


Concurrency in a DBMS

Users submit transactions, and can think of each transaction as executing by itself. Concurrency is achieved by the DBMS, which interleaves

actions (reads/writes of DB objects) of various transactions. Each transaction must leave the database in a consistent

state if the DB is consistent when the transaction begins. DBMS will enforce some ICs, depending on the ICs

declared in CREATE TABLE statements. Beyond this, the DBMS does not really understand the

semantics of the data. (e.g., it does not understand how the interest on a bank account is computed).

Issues: Effect of interleaving transactions, and crashes.


Example (Contd.)

Consider a possible interleaving (schedule):

T1: A=A+100, B=B-100 T2: A=1.06*A, B=1.06*B

This is OK. But what about:T1: A=A+100, B=B-100 T2: A=1.06*A, B=1.06*B

The DBMS’s view of the second schedule:

T1: R(A), W(A), R(B), W(B)T2: R(A), W(A), R(B), W(B)


Summary

Concurrency control and recovery are among the most important functions provided by a DBMS.

Users need not worry about concurrency. System automatically inserts lock/unlock requests and

schedules actions of different transactions in such a way as to ensure that the resulting execution is equivalent to executing the transactions one after the other in some order.

Write-ahead logging (WAL) is used to undo the actions of aborted transactions and to restore the system to a consistent state after a crash.

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