DATABASE DESIGN
Chapter-2- Database System
Concepts and Architecture
Reference:
Elmasri
Lec.
1
and Navathe, Fundamentals of Database Systems, Fifth Edition
Fatimah Al-Aqeel Lecture slides
DATA MODELS
Data Model:
A set of concepts to describe the structure of a
database (the data types, entity, relationships
and constraints that should hold for the data),
and certain constraints that the database should
obey.
Structure of a database:
Entity: Represent a real-world objects or
concepts. (ex: employee)
 Attribute: Represent some property of interest
that describes an entity. (ex: salary, name)
 Relationship: among two or more entities. (ex: a
works-on relationship between an employee and
a project)

DATA MODELS
Data Model Operations:
Operations for specifying database retrievals
and updates by referring to the concepts of
the data model. Operations on the data model
may include basic operations and userdefined operations. (An example of userdefine operation is COMPUTE-GPA which
can be applied to the Student object)
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.)
 Physical (low-level, internal) data models:
Provide concepts that describe details of how
data is stored in the computer.
 Implementation (representational) data
models: Provide concepts that fall between the
above two, balancing user views with some
computer storage details.

CATEGORIES OF DATA MODELS
Conceptua
l
model
Logical
model
Physical
model
• Hardware independent/Software
independent
• (high-level, semantic)data models
• Hardware independent/Software
dependent
• (Representational)data models
• Hardware dependent Software
dependent
• (low-level, internal)data models
CATEGORIES OF DATA MODELS
High Level
(Conceptual Data Model)
Representational
(implementation Data Model)
Low Level
(Physical Data Model)
Provides concepts close to the way
Many users see data
Provides concepts may be understood
by end users but are not far from the
way the data is organized.
(Entities, Attributes, Relationships)
Relational Data Model widely used
Details of how data is stored in
the computer. (Computer specialist)
(Records format, ordering, access
paths : makes the search for a record
more efficient)
6
SCHEMAS VERSUS INSTANCES
Database Schema:
The description of a database including
descriptions of the database structure and the
constraints that should hold on the database.
 Schema Diagram:
A diagrammatic display of (some aspects of) a
database schema.
 Schema Construct:
A component of the schema or an object within
the schema, e.g., STUDENT,COURSE.

DATABASE SCHEMA
Three-Schema Architecture:
Proposed to support DBMS characteristics of:


Program-data independence.
Support of multiple views of the data.
THREE-SCHEMA ARCHITECTURE
THREE-SCHEMA ARCHITECTURE
10
•Internal level: describes how data is stored. The way
perceived by the DBMS & OS.
•Conceptual level: describes what data stored in DB,
and the relationships among the data. The way
perceived by the DBA & programmers.
•External level: describes the part of the DB that user
is interested in. The way perceived by the end users.
THREE-SCHEMA ARCHITECTURE
External
Level
Emp_No
Conceptual
Level
Internal
Level
View 1
FName
View 2
LName
Dept_No
EMPLOYEE
Emp_No
FName
LName
Dept_No
Salary
PREFIX
EMP#
LNM
FNM
DPT#
PAY
Staff_No LName Salary
CHAR(6)
CHAR(15)
CHAR(15)
CHAR(3)
NUMBER(5)
TYPE=BYTE(6),OFFSET=0
TYPE=BYTE(6),OFFSET=6, INDEX=EMPX
TYPE=BYTE(15),OFFSET=12
TYPE=BYTE(15),OFFSET=27
TYPE=BYTE(4),OFFSET=42
TYPE=FULLWORD,OFFSET=46
11
MAPPING
Mapping is the process of transforming requests and results
between the Internal, Conceptual & External levels.
Two types of mapping:
- External / Conceptual mapping
-Conceptual / Internal mapping
12
DATABASE STATE

Database Instance:
The actual data stored in a database at a particular moment
in time. Also called database state (or occurrence).

Database State:
Refers to the content of a database at a moment in time.

Initial Database State:
Refers to the database when it is loaded

Valid State:
A state that satisfies the structure and constraints of the
database.

Distinction
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.

DATA INDEPENDENCE

Logical Data Independence:
The capacity to change the conceptual schema without
having to change the external schemas and their
application programs.

Physical Data Independence:
The capacity to change the internal schema without
having to change the conceptual schema.
DATA INDEPENDENCE
When a schema at a lower level is changed,
only the mappings between this
schema and higher-level schemas need to
be changed in a DBMS that fully supports
data independence. The higher-level
schemas themselves are unchanged.
Hence, the application programs need not
be changed since they refer to the external
schemas.
DATA INDEPENDENCE
External
Schema
External
Schema
External/Conceptual
Mapping
External
Schema
Logical data Independence
Conceptual
Schema
Conceptual/Internal
Mapping
Physical data Independence
Internal
Schema
1- LOGICAL DATA INDEPENDENCE
The ability to change the conceptual schema
without affecting the external schemas.
(application programs)
 Ex: adding/ removing a record or a data item
 The external schema that refer to the remaining
data should not be affected.

17
2- PHYSICAL DATA INDEPENDENCE


The ability to change the internal schema
without affecting the conceptual or
external schemas.
This change might be for reorganizing the
physical files. EX: creating new access
structures to improve the performance of
retrieval or update.( i.e. change in the
physical files does not affect the queries)
18
DBMS LANGUAGES

DDL (Data Definition Languages)
Conceptual schema
 Internal schemas (when schema separation is not clear)
 External schema (in most DBMSs)


SDL (Store Definition Languages)


VDL (View Definition Languages)


External view
DML (Data Manipulation Languages)


Internal schema
To manipulate the populated data
Modern DB  All in one  (E.g. SQL)

Separate SDL
19
DBMS LANGUAGES

Data Definition Language (DDL):
Used by the DBA and database designers to specify the
conceptual schema of a database. In many DBMSs,
the DDL is also used to define internal and external
schemas (views).

In some DBMSs:
separate Storage Definition Language (SDL) and View
Definition Language (VDL) are used to define
internal and external schemas.
DBMS LANGUAGES
Data
Definition
Language
(DDL)
is a
descriptive language for defining the database
schema
DDL compiler generates meta-data stored in a the
data dictionary
21
DBMS LANGUAGES



Data Manipulation Language (DML):
Is a language for retrieving and updating (insert,
delete, & modify) the data in the DB
DML commands (data sublanguage) can be
embedded in a general-purpose programming
language (host language), such as COBOL, C or an
Assembly Language.
Alternatively, stand-alone DML commands can be
applied directly (query language).
22
DBMS LANGUAGES
Two classes of languages
•High Level or Non-procedural Languages:
• e.g., SQL,
• are set-oriented and specify what data to retrieve
than how to retrieve.
•Also called declarative languages.
• Low Level or Procedural Languages:
•record-at-a-time;
• they specify how to retrieve data and include
constructs such as looping.
23
DBMS INTERFACES
Stand-alone query language interfaces.
 Programmer interfaces for embedding DML in
programming languages:




Pre-compiler Approach
Procedure (Subroutine) Call Approach
User-friendly interfaces:





Menu-based, popular for browsing on the web
Forms-based, designed for naïve users
Graphics-based (Point and Click, Drag and Drop etc.)
Natural language: requests in written English
Combinations of the above
OTHER DBMS INTERFACES
Speech as Input (?) and Output
 Web Browser as an interface
 Parametric interfaces (e.g., bank tellers) using
function keys.
 Interfaces for the DBA:

Creating accounts, granting authorizations
 Setting system parameters
 Changing schemas or access path

SOFTWARE COMPONENTS OF A DBMS
DBMS Component Modules
 Database System Utilities
 Tools
 Application Environments

26
DBMS COMPONENT MODULES
Application
programmers
DBA Staff
APPLICATION
PROGRAMS
Casual users
Precompiled
DDL STATEMENTS
PRIVILEGED COMMANDS
Parametric users
INTERACTIVE QUERY
Host Language Compiler
DDL Compiler
Query Compiler
DML STATEMENTS
COMPILED (CANNED)
TRANSACTIONS
execution
System Catalog/
Data Dictionary
execution
DML Compiler
Run-time Database
Processor
execution
Concurrency Control/
Backup/Recovery
Subsystems
Stored Data Manager
STORED DATABASE
DBMS COMPONENT MODULES (2/2)



Disk access control
 OS:DB & catalog are stored on disk .Access to disk is controlled by
OS which schedules disk input/output.
 Stored Data Manager: controls access to DBMS information
stored in the disk.
Compilers
 DDL Compiler : process schema definition specified in the DDL,
and stores the description of the schema (meta-data) in the DBMS
catalog.
 Query Compiler: handles high- level queries that are entered
interactively.
 DML Compiler
 Precompiler /Host language compiler: extracts DML
commands from an application program written in a host
programming language. These commands are sent to the DML
complier for compilation into object code for database access.
Handling DB access at runtime
 Runtime database processor
28
DATABASE SYSTEM UTILITIES
1.
2.
3.
4.
Loading: load/transfer existing data files
(e.g. text files or sequential files) into the
database.
Backup: backup copy of the database by
dumping the entire databases onto tape.
File reorganization: to improve
performance
Performance Monitoring: monitors
database usage and provides statistics to
the DBA.
29
TOOLS



CASE( Computer Aided Software
Engineering Tools): used in the design phase of
database system. Used by DB
designers/DBA/users
Examples:
 Oracle’s Designer/Developer
 Powersoft’s S- Designer tool.
 Information Engineering Facility (IEF) to implement the ER.
Data repository systems (Information
repository)


Used in large organizations, accessed directly by users
or DBA
Stores :
 Catalog information (schema, constraints).
 Design decisions, Usage standards , application
program descriptions and user information
30
APPLICATION DEVELOPMENT
ENVIRONMENTS
E.g. PowerBuilder/JBuilder
 Supports






Development of database applications
Database design
GUI development
Querying and updating
Application program development
31
DBMS CLASSIFICATION BASED ON
DATA MODEL
Relational data model
 Hierarchical data model
 Network data model

32
DBMS CLASSIFICATION BASED ON
DATA MODEL
DBMS CLASSIFICATION BASED ON
NUMBER OF SITES (VIEW OF CONTROL)
Centralized systems
 Distributed DBMSs (DDBMS)

Homogeneous DDBMS
 Heterogeneous DBMS (Federated DBMS/multidatabase systems)

34
CHAPTER -2- SUMMARY
 Data
Model
 Database schema and Database state
 Three Schema Architecture
 Mapping
 Data Independence
 Database Languages & Interfaces
 The Database System Environment
 DBMS Classifications
35