Database Languages Architecture Data Model.pptx

CSC271 Database Systems
Lecture # 4

Summary: Previous Lecture
 ANSI-SPARC three-level architecture
 Schemas, mappings, and instances
 Data independence

Database Languages
 Data sublanguage consist of two parts:
 DDL (Data Definition Language)
 DML (Data Manipulation Language)
 Data sublanguage
 Does not include constructs for all computing needs such
as iterations or conditional statements
 Many DBMSs provide embedding the sublanguage in a
high level programming language e.g. C, C++, Java etc.
 In this case , these high level languages are called host
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
 System catalog (data dictionary, data
directory)
 Metadata (data about data, data
description, data definitions)

Data Manipulation Language (DML)
 Provides basic data manipulation
operations on data held in the database
 Procedural DML
 Non-Procedural DML

Procedural DML
 Allows user to tell system exactly how to
manipulate data
 Operate on records individually
 Typically, embedded in a high level language
 Network or hierarchical DMLs
 More work is done by user (programmer)

Non-Procedural DML
 Allows user to state what data is needed
rather than how it is to be retrieved
 Operate on set of records
 Relational DBMS include e.g. SQL, QBE etc.
 Easy to understand and learn than procedural DML
 More work is done by DBMS than user
 Provides considerable degree of data independence
 Also called declarative languages

Fourth Generation Languages (4GLs)
 No clear consensus
 Forms generators
 Report generators
 Graphics generators
 Application generators
 Examples : SQL and QBE

Functions of a DBMS
 Data storage, retrieval, and update
 A user-accessible catalog
 Transaction support
 Concurrency control services
 Recovery services

Functions of a DBMS..
 Authorization services
 Support for data communication
 Integrity service
 Services to promote data independence
 Utility services

DBMS Environment
 Single user
 Multi-user
Teleprocessing
File-Server Architecture
Client-Server Architecture

Teleprocessing
 Traditional architecture
 Single mainframe with a number of
terminals attached
 Trend is now towards downsizing

File-Server Architecture
 DBMS and applications run on each
workstation
 Disadvantages include:
 Significant network traffic
 Copy of DBMS on each workstation
 Concurrency, recovery and integrity control more
complex because multiple DBMSs accessing same files

Client-Server Architecture
 Client (tier 1) manages user interface and
runs applications
 Server (tier 2) holds database and DBMS
 Advantages include:
 Wider access to existing databases
 Increased performance
 Possible reduction in hardware costs
 Reduction in communication costs
 Increased consistency

Three-Tier Client-Server
 Client side issues in two-tier client/server
model preventing true scalability:
‘Fat’ client, requiring considerable resources on client’s
computer to run effectively
 Significant client side administration overhead
 By 1995, three layers proposed, each
potentially running on a different platform

Three-Tier Client-Server
 Advantages:
 ‘Thin’ client, requiring less expensive hardware
 Application maintenance centralized
 Easier to modify or replace one tier without affecting
others
 Separating business logic from database functions makes
it easier to implement load balancing
 Maps quite naturally to Web environment

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

Purpose of Data Model
 To represent data in an understandable way
 Represents the organization itself
 Helps in unambiguous and accurate communication
between between database designers and end-users about
their understanding of the organizational data

Components of a Data Model
 A data model comprises:
 A structural part
 A manipulative part
 Possibly a set of integrity rules
ANSI-SPARC architecture related models
 External data model (Universe of Discourse)
 Conceptual data model (DBMS independent)
 Internal data model

Categories of Data Models
 Categories of data models include:
 Object-based
 Entity-Relationship
 Semantic
 Functional
 Object-Oriented
 Record-based
 Relational Data Model
 Network Data Model
 Hierarchical Data Model
 Physical

Conceptual Modeling
 Conceptual modeling is process of
developing a model of information use in an
enterprise that is independent of
implementation details
 Should be complete and accurate representation of an
organization’s data requirements
 Conceptual schema is the core of a system supporting all
user views
 Conceptual vs. logical data model

Summary
 Database languages
 Functions of a DBMS
 DBMS environment
 Data models and their categories

References
 All the material (slides, diagrams etc.) presented in this
lecture is taken (with modifications) from the Pearson
Education website given below
http://www.booksites.net/connbegg

Database Languages Architecture Data Model.pptx

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