1 Chapter 2 Database Environment Pearson Education 2009.

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Chapter 2

Database Environment

Pearson Education © 2009

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Chapter 2 - Objectives

Purpose of three-level database architecture. Contents of external, conceptual, and internal levels. Purpose of external/conceptual and

conceptual/internal mappings. Meaning of logical and physical data independence. Distinction between DDL and DML. A classification of data models.


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Chapter 2 - Objectives

Purpose/importance of conceptual modeling. Typical functions and services a DBMS should

provide. Function and importance of system catalog. Software components of a DBMS. Meaning of client–server architecture and

advantages of this type of architecture for a DBMS.

Function and uses of Transaction Processing Monitors.


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Objectives of Three-Level Architecture

All users should be able to access same data.

A user’s view is immune to changes made in other views.

Users should not need to know physical database storage details.


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Objectives of Three-Level Architecture

DBA should be able to change database storage structures without affecting the users’ views.

Internal structure of database should be unaffected by changes to physical aspects of storage.

DBA should be able to change conceptual structure of database without affecting all users.


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ANSI-SPARC Three-Level Architecture


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External Level– Users’ view of the database. – Describes that part of database that is relevant to a particular

user.– Entities, attributes, relationships : user interested.

Conceptual Level– Community view of the database. – Describes what data is stored in database and relationships

among the data. – Complete view of the data requirements of the organization:

independentof any storage considerations– Supports external views


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Internal Level– Physical representation of the database on

the computer. – Describes how the data is stored in the

database. – Physical implementation of the database to

achieve optimal runtime performance and storage utilization.


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Differences between Three Levels of ANSI-SPARC Architecture


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Differences between Three Levels of ANSI-SPARC Architecture


UNIVERSITY Conceptual SchemaSTUDENT (Name, Student Number, Class, Major)COURSE (Course Name, Course Number, Credit, Dept)PREREQUISITE (Course Number, Prerequisite Number)SECTION (Section Id, Course Number, Semester, Year, Instructor)GRADE_REPORT(Student Number, Section Id , Grade)

UNIVERSITY External SchemaTRANSCRIPT(Student Name, Course Number, Grade, Semester, Year, Section Id) derived from STUDENT, SECTION, GRADE_REPORT

PREREQUISITES(Course Name, Course Number, Prerequisites) derived from PREREQUISITE, COURSE

ANSI-SPARC Three-Level Architecture: Schemas


Overall description of the database: Database schema specified during database design

3 different types of schema:– External (subschemas) – Conceptual – Internal

Only 1 conceptual & internal schema

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ANSI-SPARC Three-Level Architecture: Schemas


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ANSI-SPARC Three-Level Architecture: Mappings

DBMS: – responsible for mapping between these schemas.– Check the schemas for consistency

Mappings:– Conceptual/Internal mapping

» Enables DBMS to find the actual record/combinations of records in physical storage && any constraints

– External/Conceptual mapping» Enables DBMS to map names in the user’s view to the relevant

part of the conceptual schema


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Data Independence

Major objective of the three-level architecture: provide data independence.

Two types:– Logical– Physical


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Data Independence

Logical Data Independence– Refers to immunity of external schemas to

changes in conceptual schema.– Conceptual schema changes (e.g.

addition/removal of entities/attributes/relationships).

– Should not require changes to external schema or rewrites of application programs.


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Data Independence

Physical Data Independence– Refers to immunity of conceptual schema to

changes in the internal schema.– Internal schema changes (e.g. using different

file organizations, storage structures/devices).– Should not require change to conceptual or

external schemas.


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Data Independence and the ANSI-SPARC Three-Level Architecture


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Database Languages

Data Definition Language (DDL)– Allows the DBA or user to describe and

name entities, attributes, and relationships required for the application

– plus any associated integrity and security constraints.


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Database Languages Data Manipulation Language (DML)

– Provides basic data manipulation operations on data held in the database.

Procedural DML – allows user to tell system exactly how to

manipulate data. Non-Procedural DML

– allows user to state what data is needed rather than how it is to be retrieved.

Fourth Generation Languages (4GLs)– nonprocedural


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Database Languages Fourth Generation Languages (4GLs)

– Nonprocedural– Includes:

» Presentation languages – query languages, report generators

» Speciality languages – spreadsheets, database languages

» Application generators that define insert, update, retrieve data from the database to build applications

» Very high-level languages that are used too generate application code


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Data Model

Integrated collection of concepts for describing data, relationships between data, and constraints on the data in an organization.

Representation of real world objects and events and their association.

Represents the organization itself


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Data ModelData Model comprises:– a structural part

» a collection of data structures which are used to create databases representing the entities or objects modeled by the database.

» A set of rules according to which databases can be constructed

– a manipulative part» a collection of operators which can be applied to the data structures, to

update and query the data contained in the database.» Defining the types of operation that are allowed on the data.

– possibly a set of integrity rules» a collection of rules governing the constraints placed on these data

structures to ensure structural integrity.» Ensures that the data is accurate


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Data Model

Purpose– To represent data in an understandable way.– Can be used to design a database.

Categories of data models include:– Object-based– Record-based– Physical


Describe data at the conceptual & external levels

Describe data at the internal level

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Data Models: Object-Based Data Models

Use concept such as entities, attributes and relationships.

Some of the common types of object-based data model:– Entity-Relationship (ER)– Semantic – Functional– Object-Oriented.


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Data Models: Record-Based Data Models

Database consists of a number of fixed-format records Each record type defines a fixed number of fields –

fixed length Three types:

– Relational Data Model– Network Data Model– Hierarchical Data Model.


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Relational Data Model


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Network Data Model


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Hierarchical Data Model


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Data Models: Physical Data Models

Describe how data is stored in the computer Representing information such as record structures,

record orderings and access paths.


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Conceptual Modeling

Conceptual schema is the core of a system supporting all user views.

Should be complete and accurate representation of an organization’s data requirements.

Conceptual modeling is process of developing a model of information use that is independent of implementation details.

Result is a conceptual data model.– Also referred as logical model


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Functions of a DBMS Data Storage, Retrieval, and Update.

– Fundamental capability of a DBMS– A DBMS must furnish users with the ability to store, retrieve and

update data in the database A User-Accessible Catalog.

– A DBMS must furnish a catalog in which descriptions of data items are stored and which is accessible to users

– System catalog stores:» Names, types and sizes of data items» Names of relationships» Integrity constraints» Names of authorized users» Data items that user can access and types of access allowed» External, conceptual and internal schemas and the mappings between the

schemas» Usage statistics


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Functions of a DBMS Transaction Support.

– A DBMS must furnish a mechanism that will ensure either that all the updates corresponding to a given transaction are made or that none of them is made

Concurrency Control Services.– A DBMS must furnish a mechanism to ensure that the database is

updated correctly when multiple users are updating the database concurrently


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Functions of a DBMS Recovery Services.

– A DBMS must furnish a mechanism for recovering the database in the event that the database is damaged in anyway.

– Database has to be returned to a consistent state. Authorization Services.

– A DBMS must furnish a mechanism to ensure that only authorized users can access the database.

Support for Data Communication.– A DBMS must be capable of integrating with communication

software.– DBMS should be capable to integrate with a variety of Data

Communication Manager (DCM).


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Functions of a DBMS Integrity Services.

– A DBMS must furnish a means to ensure that both the data in the database and changes to the data follow certain rules.

– Database integrity: correctness and consistency of stored data.– Integrity:

» Concerned with the quality of data.» Expressed in terms of constraints.

Services to Promote Data Independence.– A DBMS must include facilities to support the independence of

programs from the actual structure of the database


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Functions of a DBMS Utility Services.

– A DBMS should provide a set of utility services.– Help DBA administer the database effectively– Example:

» Import/export facilities» Monitoring facilities» Statistical analysis programs» Index reorganization facilities


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System Catalog

Repository of information (metadata) describing the data in the database.

One of the fundamental components of DBMS. Typically stores:

– names, types, and sizes of data items;– constraints on the data;– names of authorized users;– data items accessible by a user and the type of

access;– usage statistics.


1 Chapter 2 Database Environment Pearson Education 2009.

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