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Introduction to Database Systems Chpt 1. Instructor: Xintao Wu. http://www.sigmod.org/record/issues/0606/index.html. History. 60s C. Bachman GE network data model Late 60s IBM IMS hierarchical data model 70 E.Codd relational model

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introduction to database systems chpt 1

Introduction to Database SystemsChpt 1

Instructor: Xintao Wu

Ramakrishnan & Gehrke

history

History

60s C. Bachman GE network data model

Late 60s IBM IMS hierarchical data model

70 E.Codd relational model

80s SQL IBM R trasaction J. Gray

Late 80s-90s DB2, Oracle, informaix, sybase

90s- DW, internet

Turing award and Turing test?

Turing award listTuring website

Ramakrishnan & Gehrke

what is a dbms
What Is a DBMS?
  • A very large, integrated collection of data.
  • Models real-world enterprise.
    • Entities (e.g., students, courses)
    • Relationships (e.g., Madonna is taking ITCS6160)
  • A Database Management System (DBMS)is a software package designed to maintain and utilize databases.

Ramakrishnan & Gehrke

why use a dbms
Why Use a DBMS?
  • Data independence and efficient access.
  • Reduced application development time.
  • Data integrity and security.
  • Uniform data administration.
  • Concurrent access, recovery from crashes.

Ramakrishnan & Gehrke

why study databases
Why Study Databases??
  • Shift from computation to information
    • at the “low end”: scramble to webspace
    • at the “high end”: scientific applications
  • Datasets increasing in diversity and volume.
    • Digital libraries, interactive video, Human Genome project, EOS project
    • ... need for DBMS exploding
  • DBMS encompasses most of CS
    • OS, languages, theory, “A”I, multimedia, logic

Ramakrishnan & Gehrke

data models
Data Models
  • A data modelis a collection of concepts for describing data.
  • Aschemais a description of a particular collection of data, using the given data model.
  • The relational model of datais the most widely used model today.
    • Main concept: relation, basically a table with rows and columns.
    • Every relation has a schema, which describes the columns, or fields.

Ramakrishnan & Gehrke

levels of abstraction
Levels of Abstraction

View 1

View 2

View 3

  • Many views, single conceptual (logical) schemaand physical schema.
    • Views describe how users see the data.
    • Conceptual schema defines logical structure
    • Physical schema describes the files and indexes used.

Conceptual Schema

Physical Schema

  • Schemas are defined using DDL; data is modified/queried using DML.

Ramakrishnan & Gehrke

example university database
Example: University Database
  • Conceptual schema:
    • Students(sid: string, name: string, login: string,

age: integer, gpa:real)

    • Courses(cid: string, cname:string, credits:integer)
    • Enrolled(sid:string, cid:string, grade:string)
  • Physical schema:
    • Relations stored as unordered files.
    • Index on first column of Students.
  • External Schema (View):
    • Course_info(cid:string,enrollment:integer)

Ramakrishnan & Gehrke

data independence
Data Independence
  • Applications insulated from how data is structured and stored.
  • Logical data independence: Protection from changes in logical structure of data.
  • Physical data independence: Protection from changes in physical structure of data.
  • One of the most important benefits of using a DBMS!

Ramakrishnan & Gehrke

structure of a dbms

Query Optimization

and Execution

Relational Operators

Files and Access Methods

Buffer Management

Disk Space Management

DB

Structure of a DBMS

These layers

must consider

concurrency

control and

recovery

  • A typical DBMS has a layered architecture.
  • The figure does not show the concurrency control and recovery components.
  • This is one of several possible architectures; each system has its own variations.

Ramakrishnan & Gehrke

transaction management acid properties
Transaction Management: ACID properties
  • Atomicity: All actions in the Xact happen, or none happen.
  • Consistency: If each Xact is consistent, and the DB starts consistent, it ends up consistent.
  • Isolation: Execution of one Xact is isolated from that of other Xacts.
  • D urability: If a Xact commits, its effects persist.
  • The Recovery Manager guarantees Atomicity & Durability.

Ramakrishnan & Gehrke

motivation of concurrency control
Motivation of concurrency control
  • Consistency
  • Isolation
  • Example
    • Two parallel transactions T1 and T2
    • Serial execution
    • Execution with interleaving actions
    • Example shown on board

Ramakrishnan & Gehrke

motivation of recovery management
Motivation of recovery management
  • Atomicity:
    • Transactions may abort (“Rollback”).
  • Durability:
    • What if DBMS stops running? (Causes?)
  • Desired Behavior after system restarts:
    • T1, T2 & T3 should be durable.
    • T4 & T5should be aborted (effects not seen).

crash!

T1

T2

T3

T4

T5

Ramakrishnan & Gehrke

databases make these folks happy
Databases make these folks happy ...
  • End users and DBMS vendors
  • DB application programmers
    • E.g. smart webmasters
  • Database administrator (DBA)
    • Designs logical /physical schemas
    • Handles security and authorization
    • Data availability, crash recovery
    • Database tuning as needs evolve

Must understand how a DBMS works!

Ramakrishnan & Gehrke

summary
Summary
  • DBMS used to maintain, query large datasets.
  • Benefits include recovery from system crashes, concurrent access, quick application development, data integrity and security.
  • Levels of abstraction give data independence.
  • A DBMS typically has a layered architecture.
  • DBAs hold responsible jobs and are well-paid!
  • DBMS R&D is one of the broadest, most exciting areas in CS.

Ramakrishnan & Gehrke