The Worlds of Database Systems

Chapter 1

Database Management Systems (DBMS)

• DBMS: Powerful tool for creating and managing large amounts of data efficiently and allowing it to persist over long periods of time safely

• DBMS capabilities– Persistent storage– Programming interface– Transaction management

DBMS vs File Systems

• Conventional file systems are inadequate as database systems.

• They fail to support:– Efficient search– Efficient modifications to small pieces of data– Complex queries– Controlled buffering of useful data in MM– Atomic and independent execution of

transactions

DBMS Functionalities

• Allows users to create new databases

• Allows users to querry data

• Support the storage of very large amounts of data

• Controls access to data from many users at once

Early Database Management Systems

• Airline reservation systems

• Banking systems

• Corporate Records

Airline Reservation System• Data

– Reservations (flight no, seat, meal prefer.)– Flights (src, dest, departure/arrival times, etc)– Prices

• Queries– Flights on a given date, time, city, seats available,

prices• Modifications

– Booking a flight, assigning a seat• Requirements

– Concurrent access by many agents (make sure no two agents assign the same seat simultaneously)

– Avoid loss in case of a sudden system failure

Relational Databases

• Based on the relational model

• Separates the logical view from the physical view of the data.

Student Course Quarter

Charles CS 444 Fall, 1997

Dan CS 142 Winter,1998

… … …

Querying a Database

• Find all the students who have taken CS444 in Fall, 1997.

• S(tructured) Q(uery) L(anguage)– select E.name– from Enroll E– where E.course=CS444 and – E.quarter=“Fall, 1997”

• Query processor figures out how to answer the query efficiently.

Database Industry

• Relational databases are a great success of theoretical ideas.

• “Big 3” DBMS companies are among the largest software companies in the world.

• IBM (with DB2) and Microsoft (SQL Server, Microsoft Access) are also important players.

• $20B industry• Challenged by object oriented DBMS.

Evolution • Smaller and smaller systems

– DBMS’s could only be run on large computers (only large computers could store gigabyte)

– Now, feasible to run a DBMS on a PC

• Bigger and bigger systems– Many applications need hundreds of gigabyte

• E.g. A retail chain may store terabytes (1012)

– Newer databases store images, audio, video, etc.• E.g., database of sattellites images store petabytes (1015)

– Modest size databases stored in Secondary Storage (Arrays of disks)

Dealing with large data

• One could argue that what distinguishes database systems from other software is, database systems assume that data is too big to fit in main memory; thus kept on disk

• Tertiary Storage– Capacity of terabytes– Access times seconds (ms for disks)– CD’s DVD’s may be the storage medium

• Parallel Computing– Satisfies the need of fast access to large data– Speeds up through parallel access to disks/devices– Needs efficient algorithms to intelligently break queries up

• Client-Server and Multi-Tier Architectures– Major database components at the server and the

client used to interface with the user– In multi-tier architectures, client is an application

server, manages connections to the database, transactions, authorization, etc.

– Client application server database server• Multimedia Data• Information Integration

– Providing a unified view to the database user even if data comes from different sources(legacy databases) using different structures to represent information

– Data Warehouses copy information from many legacy databases with appropriate translation to a central database;

• Warehouses reconstructed each night to reflect updates on legacy databases

Overview of a DBMS• DDL: Data Definition Language

– Capable of altering the metadata (schema or structure/constraints information of the database)

– Requires special authority (i.e., used by database administrator)

• Storage and Buffer Management– Storage manager keeps track of the location of files

on the disk and obtains the blocks containing a file on request from the buffer manager which keeps portions of the disk contents in MM. Information that various components may need include

• Data, Metadata, Statistics• İndexes: data structures that support efficient access to the

data

DBMS Components

Transaction Processing– Group of one or more database operations into a

transaction which must be executed atomically and in isolation of other trans.

– A DBMS guarantees durability: the work of a completed transaction will never be lost.

– The Transaction processor performs 3 tasks.1) Logging: Every change in the database is logged on disk

(through buffer manager) to enable recovery in case of a crash2) concurrency control assures

* atomicity: a transaction is performed either completely or not at all

* isolation: transactions are executed as if there were no other concurrently executing transactions (uses locks)

3) deadlock resolution (“roll back” or “abort” some transaction)

• Querry Processing• Querry compiler

– Parser: builds a tree structure from the textual form of the query

– Preprocessor: performs semantic checks on the query and translates parse tree into algebraic operators representing the initial query plan

– Optimizer: transforms the initial query plan into the best available sequence of operations on actual data

• Execution engine– Executes the steps of the chosen query plan– Needs to interact with most of the other components of

the DBMS

DBMS Components

DBMS Studies

• Database Design– E-R Model– Relational data model– ODL

• Database programming– SQL– OQL (Object Query Language)

• Database system implementation– Storage management– Query processing– Transaction management