This document discusses database system concepts and architecture. It covers topics such as data models, schemas, and the three-schema architecture. Specifically, it describes different data models including hierarchical, network, relational, entity-relationship, and object-oriented models. It also distinguishes between database schemas, which define the structure and constraints of a database, and database instances, which represent the actual stored data.

1. Fundamentals of Database
System
Chapter Two:
Database System Concepts
and
Architecture
Prepared by:
Misganaw Abeje
University of Gondar
College Of Informatics
Department of computer science
Misganaw.Abeje13@gmail.com

2. Outline
– Data Model
– Database modeling and its usage
– Major data models evolved
– Schemas and a database state
– The Three-Schema Architecture
– Data Independence
– Database languages
– DBMS Interfaces
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3. Data Model
 One fundamental characteristic of the database approach
is that it provides some level of data abstraction.
 Data abstraction generally refers to the suppression of
details of data organization and storage, and the
highlighting of the essential features for an improved
understanding of data.
 One of the main characteristics of the database approach
is to support data abstraction so that different users can
perceive data at their preferred level of detail.
 The data model is a collection of concepts that can be
used to describe the structure of a database, provides
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4.  Most data models also include a set of basic operations for
specifying retrievals and updates on the database.
 In addition to the basic operations provided by the data model,
it is becoming more common to include concepts in the data
model to specify the dynamic aspect or behavior of a
database application. This allows the database designer to
specify a set of valid user-defined operations that are allowed
on the database objects.
 An example of a user-defined operation could be
COMPUTE_GPA, which can be applied to a STUDENT object.
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5. Categories of Data Models
 Many data models have been proposed, which we can
categorize according to the types of concepts they use to
describe the database structure.
 High-level or conceptual data models provide concepts
that are close to the way many users perceive data,
 whereas low-level or physical data models provide
concepts that describe the details of how data is stored
on the computer storage media, typically magnetic disks.
 Concepts provided by low-level data models are
generally meant for computer specialists, not for end
users.
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6.  Between these two extremes is a class of representational
(or implementation) data models, which provide concepts
that may be easily understood by end users but that are not
too far removed from the way data is organized in computer
storage.
 Representational data models hide many details of data
storage on disk but can be implemented on a computer
system directly.
 Concepts are defined as abstract ideas, they are
understood to be the fundamental building block of the
database such as entities, attributes, and relationships.
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7.  An entity represents a real-world object or concept, such
as an employee or a project from the mini-world that is
described in the database.
 An attribute represents some property of interest that
further describes an entity, such as the employee’s name
or salary.
 A relationship among two or more entities represents an
association among the entities, for example, a works-on
relationship between an employee and a project. Chapter
3 presents the Entity-Relationship model—a popular
high-level conceptual data model.
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8. The Importance of Data Models
 Designers, programmers, and end users see data in
different ways(Different views of same data ). Therefore
data model provides Various degrees of data abstraction
help reconcile varying views of same data.
 Data modeling reduces complexities of database design.
 Data models Relatively simple representations of complex
real-world data structures Often graphical
 An abstraction of a real-world object or event which is
Useful in understanding complexities of the real-world
environment.
 Data modeling is iterative and progressive
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9.  Facilitate interaction among the designer, the
applications programmer, and the end user
 End users have different views and needs for data,
which is data model support multiple view of database.
 Data model organizes data for various users.
 Data model is an abstraction: Cannot draw required data
out of the data model .
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10. Types of Data Model
 Representational or implementation data models are the
models used most frequently in traditional commercial
DBMSs. These include the
 The network and hierarchical models that have been
widely used in the past.
 Relational data model, widely used as well as the so-
called legacy data models
 Object data model as an example of a new family of
higher-level implementation data models that are closer
to conceptual data models.
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12. The Hierarchical Model
 Developed in the 1960s to manage large amounts of data
for manufacturing projects
 Hierarchical Database Model in which data is stored in
the form of records and organized into a tree-like structure,
or parent-child structure, in which in parent node can have
many child nodes connected through links.
 Hierarchical structure contains levels or segments or
children's/leaf
– Segment analogous to a record type
– Set of one-to-many relationships between segments
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14. Cont..
 Advantage of Hierarchical Database Model are:
– conceptual Simplicity
– Database Security
– Data Independence
– Data integrity
 Disadvantage of Hierarchical Database Model are:
– Complex implementation
– Difficult to manage
– Is not define many-one and many-many relationship
– Lacks of standard
– Implementation programming and use Complexity
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15. The Network Model
 Created to represent complex data relationships more
effectively.
– Improves database performance.
– Imposes a database standard
 The network database model is a model for modeling the
entities in such a way that one child entity can have more
than one parent entity. In 1969, the network model was
presented by Charles Bachman.
 Conference on Data Systems Languages (CODASYL)
created the DBTG, Database Task Group (DBTG):
defined environment to facilitate database creation.
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16. Characteristics of Network Model
 The network model is better than a hierarchical model.
 Supports many to many relationships.
 Entities are represented as a connected network with each other.
 One child entity can have more than one parent entity. For example,
in the figure, the Subject has two children. One child is a STUDENT
and another one is Degree.
 Entities can have multiple parent entities and lead to a complex
structure.
 Not very flexible to reorganize the model.
 High performance than hierarchical model
 Query facility is not available in the network model.
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18. The Relational Model
 Developed by E. F. Codd (IBM) in 1970
 Table (relations)
– Matrix consisting of row/column intersections
– Each row in a relation called a tuple
 Relational models considered impractical in
1970
 Model conceptually simple at expense of
computer overhead
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19.  Relational data management system (RDBMS)
– Performs same functions provided by
hierarchical model
– Hides complexity from the user
 Relational diagram (ER Diagram)
– Representation of entities, attributes, and
relationships
 Relational table stores collection of related entities
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22. Cont…
 SQL-based relational database application
involves three parts:
– User interface
 Allows end user to interact with the data
– Set of tables stored in the database
 Each table is independent from another
 Rows in different tables related based on
common values in common attributes
– SQL “engine”
 Executes all queries
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23. The Entity Relationship Model
 Widely accepted standard for data modeling to
represent.
 Graphical representation of entities and their
relationships in a database structure
 Entity relationship diagram (ERD)
– Uses graphic representations to model
database components
– Entity is mapped to a relational table
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24. Cont…
 Entity instance (or occurrence) is row in table
 Entity set is collection of like entities
 Connectivity labels types of relationships
 Relationships expressed using Chen notation
– Relationships represented by a diamond
– Relationship name written inside the diamond
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25. The Object-Oriented (OO) Model
 Data and relationships contained in single
structure known as an object
 OODM (object-oriented data model) is the
basis for OODBMS
– Semantic data model
 Objects contain operations
 Object is self-contained: a basic building block
for autonomous structures
 Object is an abstraction of a real-world entity
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26. Cont..
 Attributes describe the properties of an object
 Objects that share similar characteristics are
grouped in classes
 Classes are organized in a class hierarchy
 Inheritance: object inherits methods and
attributes of parent class
 UML based on OO concepts that describe
diagrams and symbols
– Used to graphically model a system
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27. Data Models: A Summary
 Common characteristics:
– Conceptual simplicity with semantic completeness
– Represent the real world as closely as possible
– Real-world transformations must conform with
consistency and integrity characteristics
 Each new data model capitalized on the
shortcomings of previous models
 Some models better suited for some tasks
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29. Schemas, Instances, and Database State
 In any data model, it is important to distinguish between
the description of the database and the database itself.
The description of a database is called the database
schema, which is specified during database design and
is not expected to change frequently.
 Database Schemas is the structure of a database we
mean data types, relationships, and constraints that
hold a database.
 Schemas is important to distinguish between the
description of the database and the database itself.
 The actual data in a database may change quite
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30.  A displayed schema is called a schema diagram. Figure 2.1
shows a schema diagram for the database shown in Figure
1.2; the diagram displays the structure of each record type but
not the actual instances of records. We call each object in the
schema such as STUDENT or COURSE a schema construct.
 A schema diagram displays only some aspects of a schema,
such as the names of record types and data items, and some
types of constraints. The actual data in a database may change
quite frequently.
 The data in the database at a particular moment in time is
called a database state or snapshot. It is also called the
current set of occurrences or instances in the database.
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31. schema diagram
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32. Three-Schema Architecture
and Data Independence
 The most important characteristics of the database
approach, listed in chapter 1, some of are:
1. Use of a catalog to store the database description (schema) so
as to make it self-describing,
2. Insulation of programs and data (program-data and
program-operation independence),(data Independence)
3. support of multiple user views.
1. In this section we specify an architecture for database
systems, called the three-schema architecture, that
was proposed to help achieve and visualize these
characteristics.
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33. The Three-Schema Architecture
 The goal of the three-schema architecture, illustrated in Figure
2.2, is to separate the user applications from the physical
database which is Degrees/level of Data Abstraction.
 The three-schema architecture is a convenient tool with which
the user can visualize the schema levels in a database system.
 A complete database is much too complex a system to be
developed without first creating a simplified framework.
 Data abstraction makes it possible for the developer to start
from essential elements. data abstractions and incrementally
add data detail to create the final system.
 Database designer starts with abstracted view, then adds details
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34.  Standards Planning and Requirements Committee
(SPARC) Defined a framework for data modeling based
on degrees of data abstraction1970s): which is in three
tier architecture, schemas can be defined at the following
three levels
 External
 Conceptual
 Internal
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36. 1. The external or view level
 The external or view level includes a number of external
schemas or user views.
 Each external schema describes the part of the database
that a particular user group is interested in and hides the
rest of the database from that user group.
– End users’ view of the data environment
– ER diagrams represent external views
– External schema: specific representation of
an external view of Entities, Relationships,
Processes, Constraints.
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37. Cont…
 Easy to identify specific data required to support
each business unit’s operations.
 Facilitates designer’s job by providing feedback
about the model’s adequacy.
 Ensures security constraints in database design.
 Simplifies application program development
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39. The Conceptual Model
 The conceptual level has a conceptual schema, which
describes the structure of the whole database for a
community of users. The conceptual schema hides the
details of physical storage structures and concentrates on
describing entities, data types, relationships, user
operations, and constraints.
 Represents global view of the entire database
 All external views integrated into single global
view: conceptual schema
 Complete ER model most widely used
 ERD graphically represents the conceptual schema diagram
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41.  Provides a relatively easily understood worldwide level
view of data environment
 Independent of both software and hardware
– Does not depend on the DBMS software used to
implement the model
– Does not depend on the hardware used in the
implementation of the model
– Changes in hardware or software do not affect
database design at the conceptual level
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42. The Internal Model
 The internal level has an internal schema, which describes
the physical storage structure of the database. The internal
schema uses a physical data model and describes the
complete details of data storage and access paths for the
database.
 Representation of the database as “seen” by the DBMS, Maps
the conceptual model to the DBMS
 Internal schema depicts a specific representation of an internal
model.
 Depends on specific database software, Change in DBMS
software requires internal model be changed
 Logical independence: change internal model without affecting
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44. The Physical Model
 Operates at lowest level of abstraction
– Describes the way data are saved on storage
media such as disks or tapes.
 Requires the definition of physical storage
and data access methods.
 Relational model aimed at logical level.
– Does not require physical-level details.
 Physical independence: changes in physical
model do not affect internal model
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46. Data Independence
 The three-schema architecture can be used to further
explain the concept of data independence, which can be
defined as the capacity to change the schema at one
level of a database system without having to change the
schema at the next higher level. We can define two types
of data independence:
 Logical Data Independence Capacity to change the
conceptual schema without changing the application
programs or external schema.
 Physical data independence Capacity to change the
internal schema without changing the conceptual
schema.
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47. DBMS Languages
 Once the design of a database is completed and a DBMS
is chosen to implement the database, the first step is to
specify conceptual and internal schemas for the database
 These SQL commands are mainly categorized into four
categories as:
– DDL – Data Definition Language: Used by DBA and
Database designers to define both conceptual and
internal schemas.
– DQl – Data Query Language: DML statements are
used for performing queries on the data within schema
objects. The purpose of DQL Command is to get some
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48.  The main types of languages and interfaces that DBMSs
support.
– A data definition language (DDL) is used to define the database
conceptual schema. In most DBMSs, the DDL also defines user
views and, sometimes, storage structures; The DBMS compiles all
schema definitions and stores their descriptions in the DBMS
catalog.
– A data manipulation language (DML) is used for specifying
database retrievals and updates. DMLs can be high level (set-
oriented, nonprocedural) or low level (record oriented,
procedural). A high-level DML can be embedded in a host
programming language, or it can be used as a standalone
language; in the latter case it is often called a query language.
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49. DBMS Interfaces
 User-friendly interfaces provided by a DBMS may include the following:
1. Menu-Based Interfaces for Web Clients or Browsing. These
interfaces present the user with lists of options (called menus) that
lead the user through the formulation of a request. Menu based
Interfaces. Pull-down menus are a very popular technique in Web-
based user interfaces. They are also often used in browsing
interfaces, which allow a user to look through the contents of a
database in an exploratory and unstructured manner.
2. Forms-Based Interfaces. A forms-based interface displays a form
to each user. Users can fill out all of the form entries to insert new
data, or they can fill out only certain entries, in which case the
DBMS will retrieve matching data for the remaining entries. Forms
are usually designed and programmed for naive users as interfaces
to canned transactions.
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50. 3. Graphical User Interfaces: A GUI typically displays a
schema to the user in diagrammatic form. The user then
can specify a query by manipulating the diagram. In
many cases, GUIs utilize both menus and forms. Most
GUIs use a pointing device, such as a mouse, to select
certain parts of the displayed schema diagram.
4. Interfaces for the DBA: Most database systems contain
privileged commands that can be used only by the DBA
staff. These include commands for creating accounts,
setting system parameters, granting account
authorization, changing a schema, and reorganizing the
storage structures of a database.
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51. The Database System Environment: Database System
Utilities
 In addition to possessing the software modules just
described, most DBMSs have database utilities that
help the DBA manage the database system. Common
utilities have the following types of functions:
– Loading. A loading utility is used to load existing data files such
as text files or sequential files into the database. Usually, the
current (source) format of the data file and the desired (target)
database file structure are specified to the utility, which then
automatically reformats the data and stores it in the database.
– Backup. A backup utility creates a backup copy of the database,
usually by dumping the entire database onto tape or other mass
storage medium. The backup copy can be used to restore the
database in case of catastrophic disk failure. Incremental
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52.  Database storage reorganization. This utility can be
used to reorganize a set of database files into different
file organizations, and create new access paths to
improve performance.
 Performance monitoring. Such a utility monitors
database usage and provides statistics to the DBA. The
DBA uses the statistics in making decisions such as
whether or not to reorganize files or whether to add or
drop indexes to improve performance.
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53. DBMS Classification
 The typical and popular DBMS are ORACLE, SQL
SERVER, MySQL SERVER, PostgreSQL , SQLite…..
 We classified DBMSs according to several criteria:
– Data model: The main data model used in many current
commercial DBMSs is the relational data model.
– The number of users supported by the system. Single-
user systems support only one user at a time and are
mostly used with PCs. Multiuser systems, which
include the majority of DBMSs, support concurrent
multiple users.
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54.  The third criterion is the number of sites over which the
database is distributed. A DBMS is centralized if the data is
stored at a single computer site. A centralized DBMS can
support multiple users, but the DBMS and the database reside
totally at a single computer site. A distributed DBMS
(DDBMS) can have the actual database and DBMS software
distributed over many sites, connected by a computer network.
 The fourth criterion is cost. It is difficult to propose a
classification of DBMSs based on cost. Today we have open
source (free) DBMS products like MySQL and
PostgreSQL that are supported by third-party vendors with
additional services.
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55.  Thank you
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