2Lecture Database System Concepts(1)

8/6/2019 2Lecture Database System Concepts(1)

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Database SystemEnvironment

D Mukherjee

Assistant Professor IT Area


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DataBase System Concepts and ArchitectureDataBase System Concepts and Architecture

Data Models, Schemas, and Instances

DBMS Architecture and Data Independence

Database Languages and Interfaces

The Database System Environment

Classification of Database Management Systems

DBMS/DB SystemConepts/Lecture2/22


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Data Model: A set of concepts to describe the structure of a

database, and certain constraints that the database should obey.

data types

relationships

Provide data abstraction

Data Model Operations: Operations for specifying database

retrievals and updates by referring to the concepts of the data

model.

generic operation: insert, delete, modify, retrieve

user-defined operations

Data Models, Schemas, and InstancesData Models, Schemas, and Instances



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Categories of Data Models:

- Conceptual (high-level, semantic) data models: Provide concepts that

are close to the way many users perceive data.(Also called entity-based or object-based data models.)

entity attribute relationship

- Physical (low-level, internal) data models: Provide concepts thatdescribe details of how data is stored in the computer.

record formats record ordering access paths

- Implementation (record-oriented) data models: Provide concepts that

fall between the above two, balancing user views with some computer

storage details.

relational network hierarchicalDBMS/DB SystemConepts/Lecture2/22


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Schemas, Instances and Database StateSchemas, Instances and Database State

Database Schema (meta-data): The description of a database. Includes

descriptions of the database structure and the constraints that should holdon the database.

Schema Diagram: A diagrammatic display of (some aspects of ) a

database schema.

Database Instance: The actual data stored in a database at aparticular

moment in time. Also called database state ( or occurrence, snapshot)

The database schema changes very infrequently. The database state

changes every time the database is updated. Schema is also called

intension, whereas state is called extension.

Each schema construct has its own current set of instances.



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Schema diagram forUNIVERSITY database

schema construct

Known data:

name of record types, data items



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UNIVERSITY Database



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define

empty state

initial state

load

state

update

updatevalid state

satisfy database schema



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The Three-schema architecture



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DBMS Architecture and Data Independence

Proposed to support DBMS characteristics of: Insulation of Programs and data/programs and operations (program

data and program-operation independence) Support of Multiple views of data Use of catalogue (database description)

DBMS Schema can defined in three levels:

-Internal Schema at the internal level to describe data storage structuresand access paths. Typically uses a physical data model.

- Conceptual schema at the conceptual level to describe the structure andconstraints for the whole database. Uses a conceptual or animplementation data model.

- External schema at the external level to describe the various user views.

Usually uses the same data models the conceptual level or high leveldata model.

Mappings among schema levels are also needed. programs refer to anexternal schema and are mapped by the internal schema for execution.



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Data Independence

Logical Data Independence: The capacity to change theconceptual schema without having to change the externalschemas and their application programs.

Physical Data Independence: The capacity to change theinternal schema without having to change the conceptual

schema.When a schema at a lower level is changed, only the mappingsbetween this schema and higher-lever schemas need to bechanged in a DBMS that fully supportsdata independence. The higher-level schemas themselves are

unchanged. Hence, the application programs need not bechanged since they refer to the external schemas.



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Database Languages & Interfaces

Data Definition Language (DDL): Used by the DBA anddatabase designers to specify the conceptual schema of thedatabase. In many DBMSs, the DDL is also used to defineinternal and external schemas (views). In some DBMSs,separate storage definition language (SDL) and viewdefinition language (VDL) are used to define internal and

external schemas. Data Manipulation Language (DML): Used to specify

database retrievals and updates (insertion, deletions andmodifications) DML commands (data sublanguage) can be embedded in a

general purpose programming language (host language) Alternatively, standalone DML commands can be applied

directly (query language) provide appropriate languagesand interfaces for each category of users.



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Types of DMLTypes of DML

-Procedural DML: Also called record-at-a-time (record-oriented) or low-level DML Must be embedded in a programming language. Searches for and retrieves individual database records and uses looping

and other constructs of the host programming language to retrieve multiple

records.

-Declarative or non-procedural DML: Also called set-at-a-time (set-oriented) or high-level DML. Can be used as a stand-alone query language or can be embedded in a

programming language. Searches for and retrieves information from multiple related database

records in a single command.

- host language: general-purpose language

- data sublanguage: DML

- C++



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DBMS InterfacesDBMS Interfaces

- Stand-alone query language interfaces. (casual end

user)

- Programmer interfaces for embedding DML in

programming

languages: (programmer)

-Pre-compiler Approach-Procedure (Subroutine) Call Approach

- User-friendly interfaces:

-Menu-based Interfaces for Browsing.-Forms-based Interfaces.

-Graphical User Interfaces.

-Combination of the above



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DBMS InterfacesDBMS Interfaces

-Interfaces for Parametric Users (using function keys)

- Interfaces for the DBA:

-Creating accounts, granting authorizations-Setting system parameters

-Changing schemas or access path



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DBMS Component ModulesDBMS Component Modules

The Database System EnvironmentThe Database System Environment



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Database System UtilitiesDatabase System Utilities

To perform certain functions such as:

-Loadingdata stored in files into a database. Conversion tool

-Backing up the database periodically on storage.-File reorganizingdatabase file structures.-Report generation utilities.-Performance monitoringutilities.

-Other functions, such assorting, user monitoring,data compression, etc.



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Data dictionary utility:

- Used to store schema descriptions and other information such as design

decisions, application program descriptions, user information, usage

standards, etc.-Active data dictionary is accessed by DBMS software and users/DBA.-Passive data dictionary is accessed by users/DBA only.

Communications Facilities- Allow users at locations remote from the database system site to access

the database.

DB (DBMS)/DC (Data Communication System)

Tools, Application Environments, andTools, Application Environments, and

Communications FacilitiesCommunications Facilities



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Classification of Database Management SystemsClassification of Database Management Systems

Based on the data model used:

Data models

-Traditional: Relational, Network, Hierarchical

- Emerging: Object-oriented, Semantic, Entity- Relationship, other.

Other classifications:

Number of users : Single-user (typically used with personal computers) vs.

multi-user (most DBMSs)

Number of sites:

Centralized (uses a single computer) vs. distributed (uses multiple computers).

Homogeneous vs. HeterogeneousCost of DBMS software. $10,000~100,000

$100~3,000Purpose general purpose

special purpose

e.g. airline reservations, telephone directory, on-line transaction

processing system



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A Network Schema



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Assignment:: Type(Individual) Prepare a report on applications of

Databases with specifications of their use in

any industry of your choice. You may share

your experiences derived during the courseof your SIP.

Deadline for Submission: 7th day from date till

4:30 pm. Please dont jump deadline.

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