2. Outline
Data Models, Schemas, and Instances
Three-Schema Architecture
Database language and Interfaces
The database system environment
Centralized and client/server architecture
3. Categories of data models
High-level or Conceptual data models:
Provide concept that are close to the way many users
perceive data
Low-level or Physical data model:
Provide concepts that describe the details of how data
is stored in the computer
4. Conceptual data models
• It uses concepts such as entities, attributes and
relationships.
• Entity represents a real-world object or concept, such
as employee or project
• Attribute represents some property of interest that
further describes an entity, such as employee’s name
or salary
• Relation among two or more entities represents an
association among two or more entitles
6. Schemas and Database State
In any data model, it is important to distinguish
between the description of the data and database itself
The description of the database is called the database
schema
A displayed Schema is called a schema diagram
9. Schemas and Database State
The data in the database at a particular moment in
time is called a database state
The distinction between database schema and
database state is very important
When we define a new database, we specify its
database schema only to the DBMS
At this point, the corresponding database state is the
empty state with no data
We get the initial state of the database when the
database is first loaded
From then on, every time an update operation is
applied to the database, we get another database state
10. Schemas and Database State
Valid State: a state that satisfies the structure and
constrains specified in the schema.
The database schema changes very infrequently.
The database state changes every time the database
is updated
Schema is also called intension.
State is also called extension.
11. Outline
Data Models, Schemas, and Instances
Three-Schema Architecture
Database language and Interfaces
The database system environment
Centralized and client/server architecture
12. Three-Schema Architecture
Three of four important characteristics of the
database approach, listed in Ch.1 are:
Self-describing of a DB (Schema)
Insulation between programs and data
Support of multiple views of the data
Three-Schema Architecture : it was proposed to
help achieve and visualize these characteristics
13. Three-Schema Architecture
Defines DBMS schemas at three levels:
Internal schema at the internal level to describe
physical storage structures and access paths (e.g.
indexes).
Conceptual schema at the conceptual level to
describe the structure and constraints for the whole
database for a community of users.
External schemas at the external level to describe
the various user views.
15. Outline
Data Models, Schemas, and Instances
Three-Schema Architecture
Database language and Interfaces
The database system environment
Centralized and client/server architecture
16. DBMS Languages
The first step to create a database through DBMS is
to specify conceptual and internal schemas for the
database
Data Definition Language (DDL): is used by
database designers to define schemas
Data Manipulation Language (DML)
View Definition Language (VDL): is to specify user
views
In current DBMS, the preceding types of languages
are usually not considered distinct languages
17. DBMS Programming Language
Interfaces
Programmer interfaces for embedding DML in a
programming languages:
Embedded Approach: e.g. embedded SQL (for C, C+
+, etc.), SQLJ (for Java)
Procedure Call Approach: e.g. JDBC for Java,
ODBC for other programming languages
Database Programming Language Approach: e.g.
ORACLE has PL/SQL, a programming language based
on SQL; language incorporates SQL and its data types
as integral components
18. User-Friendly DBMS Interfaces
• Menu-based, popular for browsing on the web
(URSA)
• Forms-based, designed for naïve users
• Graphics-based
• Natural language: requests in written English
• Combinations of the above
19. Outline
Data Models, Schemas, and Instances
Three-Schema Architecture
Database language and Interfaces
The database system environment
Centralized and client/server architecture
20. DBMS Component Modules
A DBMS is a complex software system
The figure showed in next slide is divide into two
halves.
The top half refers to the various users of the database
system
The lower half shows the internals of the DBMS
responsible for storage of data and processing of
transactions
22. Outline
Data Models, Schemas, and Instances
Three-Schema Architecture
Database language and Interfaces
The database system environment
Centralized and client/server architecture
23. Centralized DBMS Architecture
A centralized DBMS in which all the DBMS
functionality, application program execution, and
user interface processing were carried out on a single
machine
24. Basic Client/Server Architectures
The client/server architecture was developed to deal
with computer environment in which a large number
of PCs, workstation, file server…
A client in this framework is typically a user machine
that provides user interface capabilities and local
processing
A server is a system containing both hardware and
software that can provide services to the client
machines.
26. Two-tier Architecture
This is called two-tire architectures because the
software components are distributed over two
systems: client and server
The emergence of the Web changed the roles of
client and server, leading to the three-tier
architecture
27. Three-tier architecture
The intermediate layer or middle layer is
sometimes called the application server or Web
server
Three-tier Architecture Can Enhance Security:
Database server only accessible via middle tier
Clients cannot directly access database server
29. Three-tier architecture
The presentation layer displays information to the
user
The business logic layer handles intermediate rules
and constrains before data is passed up to the user or
down to the DBMS
If the bottom layer is split into two layers (a web
server and a database server), then it is a 4-tire
architecture (possible to the n-tier)