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Introduction to Database Systems Chpt 1. Instructor: Xintao Wu. 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



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


Structure of a DBMS

These layers

must consider


control and


  • 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).







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


  • 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