This document discusses database system concepts and architecture. It describes DBMS architecture models as tightly integrated or client-server systems. It also discusses data models, schemas, database states, and the three schema architecture involving the internal, conceptual, and external levels. The document introduces the concepts of data independence and database languages including data definition languages and data manipulation languages.

1. 1
Chapter 2
DATABASE SYSTEM CONCEPT AND
ARCHITECTURE
• DBMS Architecture
– Tightly integrated systems architecture: the user
interface + DBMS + data are located in one place.
– Client-server system architecture:
User Interface DBMS + Data
Client Module Server Module
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Ala Hamarsheh --
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2. 2
• Data Model: a collection of concepts that used to
describe the structure of database.
 Structure: data type, constraints, and relationships.
– We use the data model to achieve some levels of data
abstraction.
– The data model should include a set of basic operations for
retrievals and updates on the DB.
• CATEGORIES OF DATA MODEL:
– High level: provide concepts that are close to the way
users perceive data (SQL).
– Low Level: provide concepts that describe the details
of how data is stored in the computer.
– Representational (implementation) data model:
provide concepts that may be understood by end
users but that are not too far from the way data is
organized within the computer (Entities)
Ala Hamarsheh --
ahamarsheh@aauj.edu

3. 3
• Schemas:
– Any data model should distinguish between the
description of the database and the database itself.
 The description of DB is called DB schema.
– Schema diagram: displays the structure of each
record type, BUT not the actual instances of
records.
StID SNAME CLASS MAJOR
STUDENT
Schema
Construct
This Schema will be
changed Infrequently
Ala Hamarsheh --
ahamarsheh@aauj.edu

4. 4
– Database State: the current set of instances or
occurrences.
 DB State will be changed frequently.
Notes:
 When we define new database we specify DB schema.
 Every time an update operation is applied to DB, we get
another DB state.
 DBMS responsible for ensuring that every state of the
database is a valid state  satisfies the structure and
constrains specified in the database schema.
 DBMS stores the description of the schema constructs
and constrains in the meta-data (catalog files).
 Schema is called intension whereas state is called
extension.
Ala Hamarsheh --
ahamarsheh@aauj.edu

5. 5
THREE SCHEMA ARCHITECTURE:
– Internal Level: to describe the data storage structure
and access paths-typically uses physical data model.
– Conceptual Schema: to describe the structure and
constraints for the whole database.-uses
implementational data model.
– External Level: to describe the various user views.
 We need mapping among these levels.
Ala Hamarsheh --
ahamarsheh@aauj.edu

6. 6
Ala Hamarsheh --
ahamarsheh@aauj.edu

7. 7
DATA INDEPENDENCE:
Changing the schema of one level of the DB system
doesn't require to change the schema of the next higher
levels.
Two types of data independence:
– Logical Data-Independence: the capacity to change
the conceptual schema without having to change the
external schema and their application programs.
– Physical Data-Independence: the capacity to
change the internal schema without having to change
the conceptual schema.
Ala Hamarsheh --
ahamarsheh@aauj.edu

8. 8
DBMS LANGUAGES:
– Data Definition language (DDL): used by DBA or
DB designers to specify the conceptual schema of a
DB.
• In many DBMSs the DDL is also used to define
internal and external schemas.
• In some DBMSs separate storage definition
language (SDL) and view definition language are
used to define internal and external schema.
– Data Manipulation Language (DML): used to
specify database retrievals and updates.
Ala Hamarsheh --
ahamarsheh@aauj.edu

9. 9
DML Commands can be:
1. Embedded in a general purpose programming
language (PL) like Java, Cobol, C++, .. Etc
2. Stand-alone, that applied directly (Query Language).
TWO TYPES OF DML:
– High-Level or Nonprocedural DML: DML
statements must be identified within the program so
that they can be extracted by the pre-compiler and
accessed by DMBS.
– Low-Level or Procedural DML: retrieves individual
records from DB and process each one separately.
 Use Looping
Ala Hamarsheh --
ahamarsheh@aauj.edu

10. 10
Ala Hamarsheh --
ahamarsheh@aauj.edu