Characteristics of Database Management System · Web view2017. 10. 7. · 1. Stores any kind of data. A database management system should be able to store any kind of data. It should

Introduction:

Databases and database technology are having a major impact on the growing use of computers. It is fair to

say that databases play a critical role in almost all areas where computers are used, including business,

electronic commerce, engineering, medicine, law, education, and library science.

A data base is a collection of related data. For example , consider the names, telephone

numbers, and addresses of the people you know. You may have recorded this data in an indexed address

book, or you may have stored it on a hard drive, using a personal computer and software such as Microsoft

Access, or Excel. This is a collection of related data with an implicit meaning and hence is a database.

Definition: A database management system (DBMS) is a collection of programs that enables

users to create and maintain a database. The DBMS is hence a general-purpose software

system that facilitates the processes of defining, constructing, manipulating, and sharing

databases among various users and applications.

1. Defining a database involves specifying the data types, structures, and constraints for the data to be

stored in the database.

2. Constructing the database is the process of storing the data itself on some storage medium that is

controlled by the DBMS.

3. Manipulating a database includes such functions as querying the database to retrieve specific data,

updating the database to reflect changes in the mini world, and generating reports from the data.

4. Sharing a database allows multiple users and programs to access the database concurrently.

NBKRIST ADBMS I M.TECH CSE I SEM Page 1

Characteristics of Database Management System1. Stores any kind of data

A database management system should be able to store any kind of data. It should not be restricted to the

employee name, salary and address. Any kind of data that exists in the real world can be stored in DBMS

because we need to work with all kinds of data that is present around us.

2. Support ACID Properties

Any DBMS is able to support ACID (Accuracy, Completeness, Isolation, and Durability) properties. It is

made sure is every DBMS that the real purpose of data should not be lost while performing transactions like

delete, insert an update. Let us take an example; if an employee name is updated then it should make sure

that there is no duplicate data and no mismatch of student information.

3. Represents complex relationship between data

Data stored in a database is connected with each other and a relationship is made in between data. DBMS

should be able to represent the complex relationship between data to make the efficient and accurate use of

data.

4. Backup and recovery

There are many chances of failure of whole database. At that time no one will be able to get the database

back and for sure company will be in a big loss. The only solution is to take backup of database and

whenever it is needed, it can be stored back. All the databases must have this characteristic.

5. Structures and described data

A database should not contains only the data but also all the structures and definitions of the data. This data

represent itself that what actions should be taken on it. These descriptions include the structure, types and

format of data and relationship between them.

6. Data integrity

This is one of the most important characteristics of database management system. Integrity ensures the

quality and reliability of database system. It protects the unauthorized access of database and makes it more

secure. It brings only the consistence and accurate data into the database.

7. Concurrent use of database

There are many chances that many users will be accessing the data at the same time. They may require

altering the database system concurrently. At that time, DBMS supports them to concurrently use the

database without any problem.


Advantages of DBMS

Controlling Data Redundancy

In non-database systems each application program has its own private files. In this case, the duplicated

copies of the same data are created in many places. In DBMS, all data of an organization is integrated into a

single database file. The data is recorded in only one place in the database and it is not duplicated.

Sharing of Data

In DBMS, data can be shared by authorized users of the organization. The database administrator manages

the data and gives rights to users to access the data. Many users can be authorized to access the same piece

of information simultaneously. The remote users can also share same data. Similarly, the data of same

database can be shared between different application programs.

Data Consistency

By controlling the data redundancy, the data consistency is obtained. If a data item appears only once, any

update to its value has to be performed only once and the updated value is immediately available to all users.

If the DBMS has controlled redundancy, the database system enforces consistency.

Integration of Data

In Database management system, data in database is stored in tables. A single database contains multiple

tables and relationships can be created between tables (or associated data entities). This makes easy to

retrieve and update data.

Integration Constraints

Integrity constraints or consistency rules can be applied to database so that the correct data can be entered

into database. The constraints may be applied to data item within a single record or the may be applied to

relationships between records.

Data Security

Form is very important object of DBMS. You can create forms very easily and quickly in DBMS. Once a

form is created, it can be used many times and it can be modified very easily. The created forms are also

saved along with database and behave like a software component. A form provides very easy way (user-

friendly) to enter data into database, edit data and display data from database. The non-technical users can

also perform various operations on database through forms without going into technical details of a fatabase.

Report Writers

Most of the DBMSs provide the report writer tools used to create reports. The users can create very easily

and quickly. Once a report is created, it can be used many times and it can be modified very easily. The

created reports are also saved along with database and behave like a software component.

Control over Concurrency

In a computer file-based system, if two users are allowed to access data simultaneously, it is possible that

they will interfere with each other. For example, if both users attempt to perform update operation on the

same record, then one may overwrite the values recorded by the other. Most database management systems

have sub-systems to control the concurrency so that transactions are always recorded with accuracy.


Backup and Recovery Procedures

In a computer file-based system, the user creates the backup of data regularly to protect the valuable data

from damage due to failures to the computer system or application program. It is very time consuming

method, if amount of data is large. Most of the DBMSs provide the 'backup and recovery' sub-systems that

automatically create the backup of data and restore data if required.

Data Independence

The separation of data structure of database from the application program that uses the data is called data

independence. In DBMS, you can easily change the structure of database without modifying the application

program.

Disadvantages of Database Management System (DBMS):

Although there are many advantages but the DBMS may also have some minor disadvantages. These are:

1. Cost of Hardware & Software:

A processor with high speed of data processing and memory of large size is required to run the DBMS

software. It means that you have to upgrade the hardware used for file-based system. Similarly, DBMS

software is also Very costly.

2. Cost of Data Conversion:

When a computer file-based system is replaced with a database system, the data stored into data file must be

converted to database files. It is difficult and time consuming method to convert data of data files into

database. You have to hire DBA (or database designer) and system designer along with application

programmers; Alternatively, you have to take the services of some software houses. So a lot of money has to

be paid for developing database and related software.

3. Cost of Staff Training:

Most DBMSs are often complex systems so the training for users to use the DBMS is required. Training is

required at all levels, including programming, application development, and database administration. The

organization has to pay a lot of amount on the training of staff to run the DBMS.

4. Appointing Technical Staff:

The trained technical persons such as database administrator and application programmers etc are required

to handle the DBMS. You have to pay handsome salaries to these persons. Therefore, the system cost

increases.

5. Database Failures:

In most of the organizations, all data is integrated into a single database. If database is corrupted due to

power failure or it is corrupted on the storage media, then our valuable data may be lost or whole system

stops.


Database Management System Vs. File Management System

A Database Management System (DMS) is a combination of computer software, hardware, and information

designed to electronically manipulate data via computer processing. Two types of database management

systems are DBMS’s and FMS’s. In simple terms, a File Management System (FMS) is a Database

Management System that allows access to single files or tables at a time. FMS’s accommodate flat files that

have no relation to other files. The FMS was the predecessor for the Database Management System

(DBMS), which allows access to multiple files or tables at a time (see Figure 1 below)


UNIT - IDatabase System Concepts: Data Models, Schemas and Instances, Three-Schema Architecture, Database Languages and Interfaces, The Database System Environment, Centralized and Client/Server Architectures for DBMSs, Classification of DBMS.Data Modeling Using ER Model: ER Diagrams, Naming Conventions, and Design Issues.EER Model: Subclasses, Super Classes, and Inheritance, Data Abstraction, Knowledge Representation and Ontology Concepts.

Data Models, Schemas and InstancesData Model: It is a collection of concepts that can be used to describe the structure of a data base.

(Consisting of the data elements, their data types, relationships).

[Or]

Defines the data structure, operations and constraints of the database.

Example data models are the relational data model, entity relationship(ER) model for defining entities and

relationships.

Example operations for retrievals and updates of the database.

Example constraints is that to take a course, you need to be a student.

1. Categories of data models:


Many data models have been proposed, which we can categorize according to the types ofconcepts they use to describe the database structure.a. Physical (low‐level, internal) data models:

• Provide concepts that describe details of how data is stored in the computer as files by showing record

formats, orderings, and access paths such as indexing structure for data retrieval.

b. Implementation (representational) data models:

• Provide concepts that fall between the above two, used by many commercial DBMS implementations (e.g.

relational data models used in many commercial systems).

c. Self‐Describing Data Models:

• Combine the description of data with the data values. Examples include XML, key‐value stores and some

NOSQL systems. Used to cater for non‐traditional data types like posts, long character blobs, and web data.

2. Schemas, Instances and Database State

The description of a database is called the database schema. This is specified during database design and

is not expected to change frequently. The fig: shows a schema diagram for the data base shown in fig:


Database state:

The data in the database at a particular moment in time is called a database state or snapshot.

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.

Initial database state:

Refers to the database state when it is initially loaded into the system.

Valid state:

A state that satisfies the structure and constraints of the database.


Three-Schema Architecture and Data Independence1) Three-Schema Architecture

DBMS uses Three-schema level architecture to achieve programs and data, support multiple views,

use of catalog to store data base description (schema). The three levels consist of

a) The external schemas for end users (E.g.: external views and different user views of data through

queries)at the external level.

b) The conceptual schemas at the conceptual level representing the whole database for a community of

users using a conceptual or implementation data model such as relational.

c) The internal schemas at the internal level which describe physical storage structures and access paths

of the database (E.g.: Indexes).

2) Data Independence

This is the ability of the DBMS to change the schema at a lower level of DB system without having to

change the schema at the next higher level.

DBMS provides the following two types of data independence.

a) Logical Data Independence

b) Physical Data Independence

a) Logical Data Independence

Logical data independence is the capacity to change the conceptual schema without having to change

external schemas or application programs. We may change the conceptual schema to expand the database


(by adding a record type or data item), to change constraints, or to reduce the database (by removing a

record type or data item).

In the last case, external schemas that refer only to the remaining data should not be affected.

For example , the external schema of fig: 1.4a should not be affected by changing the GRADE_REPORT file shown in Figure 1.2 into the one shown in Figure 1.5a.


b) Physical Data Independence

Physical data independence is the capacity to change the internal schema with out having to change the conceptual schema. Hence, the external schemas need not be changed as well. Changes to the internal schema may be needed because some physical files had to be reorganized-for example ,by creating additional access structures-to improve the performance of retrieval or update. If the same data as before remains in the database, we should not have to change the conceptual schema. For example, providing an access path to improve retrieval speed of SECTION records (Figure

1.2) by Semester and Year should not require a query such as "list all sections offered in fall 1998" to be

changed, although the query would

be executed more efficiently by the DBMS by utilizing the new access path.

All three levels of abstraction represent data descriptions only. However ,

the actual data are stored only at the physical level. The process of transforming requests and results

between levels are called mapping and done by the DBMS.


Database Languages and InterfacesThe DBMS must provide appropriate languages and interfaces for each category of users.

a) DBMS Languages

Once the design of a database is completed and a DBMS is chosen to implement the database, the first order of the day is to specify conceptual and internal schemas for the database and any mappings between the two. In many DBMSs where no strict separation of levels is maintained, one language, called the 1. Data definition language (DDL), is used by the DBA and by database designers to define both schemas. The DDL is used to specify the conceptual schema only. 2. Storage definition language (SOL), is used to specify the internal schema. The mappings between the two schemas may be specified in either one of these languages 3. View definition language (VDL), to specify user views and their mappings to the conceptual schema, but in most DBMSs the DDL is used to define both conceptual and external schemas Common DDL statements are CREATE, ALTER, and DROP.

Once the database schemas are compiled and the database is populated with data, users must have some means to manipulate the database. NBKRIST ADBMS I M.TECH CSE I SEM Page 12

Typical manipulations include retrieval, insertion, deletion, and modification of the data. The DBMS provides a set of operations or a language called the data manipulation language (DML)Common DML statements are SELECT, UPDATE, INSERT INTO and DELETE FROM

b) DBMS Interface

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. Pull-down menus are a very popular technique in Web-based user interfaces.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 fill out only certain entries, in which case the DBMS will retrieve matching data for the

remaining entries.

3. Graphical User Interfaces

A graphical interface (GUI) typically displays a schema to the user in diagrammatic form. The user can

then 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 pick certain parts of the displayed schema diagram.

4. Natural Language Interfaces

These interfaces accept requests written in English or some other language and attempt to "understand"

them. A natural language interface usually has its own "schema," which is similar to the database conceptual

schema, as well as a dictionary of important words.

5. Interfaces for Parametric Users

Parametric users, such as bank tellers, often have a small set of operations that they must perform

repeatedly. Systems analysts and programmers design and implement a special interface for each known

class of naïve users.

6. Interfaces for the DBA

Most database systems contain privileged commands that can be used only by the DBA's staff. These

include commands for creating accounts, setting system parameters, granting account authorization,

changing a schema, and reorganizing the storage structures of a database.

7. Mobile Interfaces

Interfaces allowing users to perform transactions using mobile apps


The Database System EnvironmentA DBMS is complex software system. In this section we discuss the types of software components that

constitute a DBMS and the types of computer system software with which the DBMS interacts.

1) DBMS Component ModulesThe fig 2.3 illustrates, in a simplified form, the typical DBMS components. 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.

The database and the DBMS catalog are usually stored on disk. Access to the disk is

controlled primarily by the Operating System (OS),which schedules disk input/output.

Stored Data Manager

It controls access to the DBMS information that is stored on disk. The dotted lines and circles marked

A,B,C,D and E in fig 2.3 illustrates access that are under the control of this stored data manager. The stored

data manager may use basic OS service for carrying out low level data transfer between the disk and

computer main storage.

DDL Compiler

The DDL compiler processes schema definitions.

Run-Time database processor

It handles database access at runtime. It receives retrieval or update operations and carriers them out on the

database.

Query compiler

It handles high-level queries that are entered interactively. It parses, analyzes, and compiles or interprets a query by creating database access code, and then generates calls to the runtime processor for executing the code.Pre-compilerIt extracts DML commands from an application program written in a host programming language. These commands are sent to the DML compiler for compilation into object code for database access. The rest of the program is sent to the host language compiler.Client programThe client program that accesses the DBMS running on separate computer from the computer on which the database resides. The former is called the Client computer and later it is called the database server. In some cases, the client accesses a middle computer, called the application server.


2. Database system utilities

Most DBMSs have database utilities the help the DBA in managing the database system. Common utilities

have the following types of functions:

1. 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 files and the desired (target) database file structure are

specified to the utility, which then automatically reformats the data and stores it in the database. Includes

data conversion tools.

2. Backup

A backup utility creates a backup copy of the database, usually by dumping the entire database onto tape.

3. File reorganization

This utility can be used to reorganize a database file into a different file organization to improve performance.4. Performance monitoring


Such as utility monitors database usage and provides statistics to the DBA.

Other utilities may be available for sorting files, handling data compression, monitoring access by users, interfacing with the network, and performing other functions.3. Tools, Application Environments, and Communications Facilities

Other tools provided by the DB system include:

a) Data dictionary/repository

Used to store schema descriptions and other information such as design decisions, application program

descriptions, user information, usage standards, etc.

b) Application Development Environments and CASE (Computer-aided software engineering)tools like

Forms, JBuilder, Jdeveloper, etc.

Centralized and Client/Server Architectures for DBMSs1. Centralized DBMSs Architecture

All DBMS functionality, application program execution, and user interface processing carried out on one

machine.

2. Basic Client/Server Architectures

Specialized servers with specialized functions provide database query and transaction services to the clients.

Example servers are:

Print server: All print requests by the clients are forwarded to this machine.

File server: That maintains the files of the client machine.

DBMS server


Web server

Email server

The client machines provide the user with the appropriate interfaces to utilize these servers, as well as with

local processing power to run local applications.

DBMS Example

Server handles query, update and transaction functionality

Client handles user interface programs and application programs

The fig 2.5 illustrates client/server architecture at the logical level and fig 2.6 is a simplified diagram that

shows how the physical architecture would look.

Client

User machine that provides user interface capabilities and local processing.

Server

System containing both hardware and software. It provides services to the client machines. Such as file

access, printing, archiving or database access.

3. Two-Tier Client/Server Architectures for DBMS

Server handles


Query and transaction functionality related to SQL processing.

Client handles

User interface programs and application programs.

Open Database Connectivity(ODBC)

Provides application programming interface(API). Allows client-side programs to call the DBMS, both

client and server machines must have the necessary software installed.

JDBC

Allows java client programs to access one or more DBMSs through standard interface.

4. Three-Tier and n-Tier Architectures for Web Applications

Application server or web server

Adds intermediate layer between client and the database server. Runs application programs and stores

business rules.

N-Tier

Divide the layers between the user and the stored data further into finer components.

Classification of Database Management SystemsThe classification and types of Database Management System (DBMS) is explained in a detailed manner

below based on the different factors.

1. Based on the data model

2. Based on the number of users

3. Based on the sites over which network is distributed

4. Based on the cost

5. Based on the access

6. Based on the usage

1. Based on the data model


Relational database – This is the most popular data model used in industries. It is based on the SQL. They

are table oriented which means data is stored in different access control tables, each has the key field whose

task is to identify each row. The tables or the files with the data are called as relations that help in

designating the row or record, and columns are referred to attributes or fields. Few examples are

MYSQL(Oracle, open source), Oracle database (Oracle), Microsoft SQL server(Microsoft) and DB2(IBM).

Object oriented database

The information here is in the form of the object as used in object oriented programming. It adds the

database functionality to object programming languages. It requires less code, use more natural data and also

code bases are easy to maintain. Examples are ObjectDB (ObjectDB software).

Object relational database

Relational DBMS are evolving continuously and they have been incorporating many concepts developed in

object database leading to a new class called extended relational database or object relational database.

Hierarchical database


In this, the information about the groups of parent or child relationships is present in the records which is

similar to the structure of a tree. Here the data follows a series of records, set of values attached to it. They

are used in industry on mainframe platforms. Examples are IMS(IBM), Windows registry(Microsoft).

Network database

Mainly used on a large digital computers. If there are more connections, then this database is efficient. They

are similar to hierarchical database, they look like a cobweb or interconnected network of records. Examples

are CA-IDMS(COMPUTER associates), IMAGE(HP).

2. Based on the number of users

Single user

As the name itself indicates it can support only one user at a time. It is mostly used with the personal

computer on which the data resides accessible to a single person. The user may design, maintain and write

the database programs.

Multiple users

It supports multiple users concurrently. Data can be both integrated and shared,a database should be

integrated when the same information is not need be recorded in two places. For example a student in the

college should have the database containing his information. It must be accessible to all the departments

related to him. For example the library department and the fee section department should have information


about student’s database. So in such case, we can integrate and even though database resides in only one

place both the departments will have the access to it.

3. Based on the sites over which network is distributed

Centralized database system – The DBMS and database are stored at the single site that is used by several

other systems too. We can simply say that data here is maintained on the centralized server.

Parallel network database system

This system has the advantage of improving processing input and output speeds. Majorly used in the

applications that have query to larger database. It holds the multiple central processing units and data storage

disks in parallel.

Distributed database system

In this data and the DBMS software are distributed over several sites but connected to the single computer.

4. Based on the cost


Low cost DBMS

The cost of these systems varies from $100 to $3000.

Medium cost DBMS

Cost varies from $10000 to $100000.

High cost DBMS

Costs of these systems are usually more than $100000.

5. Based on the access

This classification simply based on the access to data in the database systems

Sequential access

One after the other.

Direct access

Inverted file structures

6. Based on the usage

Online transaction processing (OLTP) DBMS

They manage the operational data. Database server must be able to process lots of simple transactions per

unit of time. Transactions are initiated in real time, in simultaneous by lots of user and applications hence it

must have high volume of short, simple queries.

Online analytical processing (OLAP) DBMS

They use the operational data for tactical and strategically decision making. They have limited users deal

with huge amount of data, complex queries.

Big data and analytics DBMS

To cope with big data new database technologies have been introduced. One such is NoSQL (not only SQL)

which abandons the well-known relational database scheme.

XML DBMS – two types

1. Native XML DBMS – Use the logical, intrinsic structure of XML document.

2. Enabled XML DBMS – Existing DBMS with facilities to store XML data and structured data in

integrated way.

Multimedia DBMS – Stores data such as text, images, audio, video and 3D games which are usually stored

in binary large object.

GIS DBMS – Stores and queries the spatial data.

Sensor DBMS – Allows to manage sensor data, bio-metric and telematics data.

Mobile DBMS – Runs on the smartphones, tablets. It handles the local queries. Supports self-management

( no DBA).


Open source DBMS – Code is publicly available and can be extended by anyone, popular for small

business applications.

http://www.studytonight.com/dbms/er-diagram.php

Data Modeling Using ER Model:

ER Diagrams, Naming Conventions, and Design Issues1. Summary of notation for ER Diagrams

What is an Entity Relationship Diagram (ERD)? An entity relationship diagram (ERD) shows the relationships of entity sets stored in a database. An entity

relationship diagram looks very much like a flowchart. It is the specialized symbols, and the meanings of

those symbols, that make it unique.

Common Entity Relationship Diagram symbols

An ER diagram is a means of visualizing how the information a system produces is related. There are five

main components of an ERD:

a) Entities

Entities are represented by rectangles. An entity is an object or concept about which you want to store

information.

A weak entity is an entity that must defined by a foreign key relationship with another entity as it cannot be

uniquely identified by its own attributes alone.

b) Actions

Actions are represented by diamond shapes, show how two entities share information in the database.

In some cases, entities can be self-linked. For example, employees can supervise other employees.


c) Attributes

Attributes are represented by ovals. A key attribute is the unique, distinguishing characteristic of the entity.

For example, an employee's social security number might be the employee's key attribute.

A multivalued attribute can have more than one value. For example, an employee entity can have multiple

skill values.

A derived attribute is based on another attribute. For example, an employee's monthly salary is based on the

employee's annual salary.

d) Connecting lines

Solid lines that connect attributes to show the relationships of entities in the diagram.

e) Cardinality specifies how many instances of an entity relate to one instance of another entity. Ordinality

is also closely linked to cardinality. While cardinality specifies the occurrences of a relationship, ordinality

describes the relationship as either mandatory or optional. In other words, cardinality specifies the maximum

number of relationships and ordinality specifies the absolute minimum number of relationships.

There are many notation styles that express cardinality.

Information Engineering Style



2. Proper Naming of Schema Constructs

Choose a singular name for entity types, rather than plural ones.

Uppercase letters for entity type and relationship type names

Attribute names have their initial letter capitalized

Lowercase letters for role names

Choose binary relationship names to make the ER diagram of the schema readable from left to right

and from top to bottom

3. Design choices for ER conceptual design

Design Choices

Should a concept be modeled as an entity or an attribute?

Should a concept be modeled as an entity or a relationship?

Identifying relationships: Binary or ternary? Aggregation?

Constraints in the ER model

A lot of data semantics can(and should)be captured.

Keep the initial ER model like the real world

E.g. don’t show foreign keys

When converting to tables, various relational database rules may change some attributes to entities.

4. Alternative Notations for ER Diagrams

Specify structural Constraints on relationships


Replaces cardinality ratio(1:1, 1:N,M:N) and single/double line notation for participation

constraints

Associate a pair of integer numbers(min,max) with each participation of an entity type E in a

relationship type R, where 0<= min<=max and max>=1

EER Model: Subclasses, Super Classes, and Inheritance

EER model The EER(Enhanced ER) model includes all the modeling concepts of the ER.

In addition, it includes the concepts of subclasses/super classes, specialization/generalization,

categories, attribute and relationship inheritance.

These are fundamental to conceptual modeling

The additional EER concepts are used to model applications more completely and more accurately

EER includes some object-oriented concepts, such as inheritance.

Subclasses, Super Classes, and Inheritance

Some objects may have similar but not identical attributes and methods. If there is a large degree of

similarity, it would be useful to be able to share the common properties. Inheritance allows one class to be


defined as a special case of a more general class. These special cases are known as subclasses and the more

general cases are known as superclasses.

An entity type may have additional meaningful subgroupings of its entities.

Example: EMPLOYEE may be further grouped into SECRETARY, ENGINEER, MANAGER,

TECHNICIAN, SALARIED_EMPLOYEE, HOURLY_EMPLOYEE,..

Each of these groupings is a subset of EMPLOYEE entities

Each is called a subclass of EMPLOYEE

EMPLOYEE is the superclass for each of these subclasses

These are called superclass/subclass relationships.

Example: EMPLOYEE/SECRETATY

EMPLOYEE/TECHNICIAN

Data Abstraction, Knowledge Representation and Ontology Concepts.Goal of Knowledge representation (KR) techniques

a) Accurately model some domain of knowledge

b) Create an ontology (An ontology is somewhat similar to a conceptual schema, but with more

knowledge, rules and exceptions) that describes the concepts of the domain and how these concepts are

interrelated

Goals of KR are similar to those of semantic data models, but there are some important similarities and

differences between the two disciplines:

Both disciplines provide concepts, constraints, operations, and languages for defining data and representing

knowledge

There are four abstraction concepts that are used in both schematic data models such as the EER model and

KR schemes


1. Classification and Instantiation

2. Identification

3. Specialization and generalization

4. Aggregation and association

5.Ontologies and the Semantic web

1. Classification and Instantiation

The process of classification involves systematically assigning similar objects/entities to object

classes/entity types.

Instantiation is the inverse of classification and refers to the generation and specific examination of distinct

objects of a class.

Exception objects

In general, the objects of a class should have a similar type structure. However, some objects may display

properties that differ in some respects from the other objects of the class.

In the EER model, entities are classified into entity types according to their basic attributes and

relationships.

One class can be instance of another class called a meta-class. Notices that this cannot be represented

directly in the EER model.

2. Identification

Identification is the abstraction process whereby classes and objects are made uniquely identifiable by

means of some identifier. For example, a class name uniquely identifies a whole class.

3. Specialization and Generalization

Generalization

Generalization is a bottom-up approach in which two lower level entities combine to form a higher level entity. In generalization, the higher level entity can also combine with other lower level entity to make further higher level entity.


Specialization

Specialization is opposite to Generalization. It is a top-down approach in which one higher level entity can be broken down into two lower level entity. In specialization, some higher level entities may not have lower-level entity sets at all.

4. Aggregation and Association

Aggregation

Aggregation is a process when relation between two entity is treated as a single entity. Here the relation between Center and Course is acting as an Entity in relation with Visitor.

Association

Association is a relationship between two objects. In other words, association defines the multiplicity

between objects. You may be aware of one-to-one, one-to-many, many-to-one, many-to-many all these

words define an association between objects. Aggregation is a special form of association. Composition is a

special form of aggregation.

Example: A Student and a Faculty are having an association.

5. Ontologies and the Semantic Web


In recent years, the amount of computerized data and information available on the Web has spiraled out of

control. Many different models and formats are used. In addition to the database models, much information

is stored in the form of documents, which have considerably less structure than database information

does.

One research project that is attempting to allow information exchange among computers on the

Web is called the Semantic Web.

Semantic Web: Allow meaningful information exchange and search among machines.

Ontology: Specification of a conceptualization.

Conceptualization: Set of concepts that are used to represent the part of reality or knowledge that is of interest to a community of users.

Specification: It refers to the language and vocabulary terms used to specify conceptualization.


Documents

Characteristics of Database Management System · Web view2017. 10. 7. · 1. Stores any kind of data. A database management system should be able to store any kind of data. It should