Different Types Of Data Models Computer Science Essay

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The structures of database is called data model. Design and implementation of any DBMS are based upon a data model. It describes data stored in the data base and its structure. The model describes the data and its relationship among several data. The database management system uses different types of models such as:

In hierarchical model data are represented in the form of record and relationship among data are represented by links. The hierarchical model represents data in the form of a tree. It resembles an upside down tree with the root at the top and the branch formed below or resembles an organization chart of a corporation. At the top level of data is the parent and data found under the root level are children. Each parent can have numerous children, but each child can have only one parent. Each child level may also be broken down into further levels with the child becoming the parent of next level as shown in the figure.

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In this figure. Stuff You Need is the parent. Stuff You Need has two children called department and items. Here each child level also be broken into further levels with the child becoming parent of next level. Here manger is the child of department and employees are children of manager. And also order is the child of item and supplier is the child of order.

The network model is similar to the hierarchical model, it is more complex, but also more flexible in accessing data items. In hierarchical structure, each parent can have more than one child, but in a network data base model each child can have more than one parent. This structure permits the connection of the nodes in a multidirectional manner. The network data box structure is a more versatile and flexible data access structure than the hierarchical type, because the root of data is not necessarily downward, it can be from any direction.

In network data model data is represented by collection of records and relationships among data are represented by links. The network model is similar to hierarchical model, but each child record can have more than one parent record. For example in the figure item has three parents called Department, Supplier and Order. This model eliminates the redundancy occurs in the hierarchical model. This model is proposed by CODASYL-DBTG (conference on Data System Languages- Database Task group) in 1971.

Network model is identified by three database components called

Network schema (database organization),

Subschema (views of database per user)

Data management language.

The network schema is only allowed to view by database administrator. It includes definition of database name, the record and the components that make up those records. The subschema lets the user to access a particular area of application in which the user designed. This areas are included in an application are record types, data items, set, types. All schemas may have different subschema but all subschemas are very different. There are several reason for creating the subschema, subschema let a user to view a different parts of database without seeing the full database. So it will give high security to the database. So no one can change or edit the database. Data management language includes data definition language (DDL) and data manipulation language (DML).

Data Definition Language (DDL)

A database schema is specified by a set of definitions expressed by a special language called data definition language (DDL), which is a language used to specify overall design of the database. The result of compilation of DDL statement is a set of tables that are stored in a special file called data dictionary or data directory. It is a file that contains data about data.

The main function of DDL

It specifies the proper data type

It specifies the length of data item

It specifies different constraints for the attribute in a table

It may specify privacy lock for preventing, accessing, data in an unauthorized user.

It gives unique name to each data item in the table

It specifies the relationship of data in a table

It may define the range of values that a data item can assume.

Data Manipulation Language (DML)

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A data manipulation language is the language that allows users to access, edit and change the data by the appropriate model. Manipulation of data would include addition, modification and removal of data from the table. Data manipulation includes the following different process.

Insertion: It is the process of adding new information into a database.

Deletion: The process in which removal of information from a table is called deletion.

Retrieval: The process in which access and process the data form a database is called retrieval.

Modification: The process in which change the data in a database is called modification.

Advantages of Network model

Easier to access

Many to many relationship can be imported

Conceptual simplicity

Data access flexibility

Data independence

Promotes database integrity

Disadvantages of Network model

The number of link is very high

New queries cannot be implemented

Relational Model

The relational model was formally introduces in 1970. The relational model was a collection of tables to represent both data and relationship among those data. Each table has multiple columns and each column has a unique name. No physical connection such as pointer is established between tables. A named table is called a relation. A relational database is composed of one or more tables. Here data is stored in the different tables made up of rows and columns. In a relational database, tables are called relations, rows are called tuples and the columns are called attributes. This model has the advantage of simple in principle; users can express their queries in a powerful query language. Another advantage of this model is that it offers flexibility. Data can be easily updated in the database. Any data that is to be changed need to update only once. The relational model or Relational database Management System (RDBMS) represents the database as a collection of relations, each of which assigned a unique name..

In a relation each row in the table represents a collection of related data values. These values can be interpreted as facts describing a real world entity or relationship. The column name of a table helps to interpret the values stored in each row of the table..

Terminologies in RDBMS

Relation: The named table is called relation. The relation is the only one data structure used in the relational model to represent both entities and the relationship between them.

Domain: A domain is a pool of values from which the actual values appearing in a given column are drawn.

Tuple: The rows of tables are generally referred to as tuples.

Attributes: The columns of tables are generally referred to as attributes.

Degree: The number of attributes in a relation determined the degree of relation.

Cardinality: The number of tuples in a relation is called cardinality of the relation.

Entity: An entity is an object which can be distinctly identified.

Primary key: A primary key is a set of one or more attributes that can be uniquely identify tuples within the relation

Foreign key: A non key attributes whose values are derived from the primary key of some other table is known as foreign key.

Advantages of Relational model

Data manipulation is easy

It is simple and powerful

It uses collection of tables

We can apply mathematical operation on tables

Easier database design, implementation, management and use

Disadvantages of Relational model

It takes huge amount of memory for holding these tables

Poor design and implementation is made easy

May promote "islands of information" problems

Entity- Relationship Model

The entity relationship model is the graphical representation of logically related entities in order to create a database. This model was first proposed by Peter-Sin-Shan Chan on 1970.

Features of E R Model

Simple

Easy to understand

Large organizations require E R Model

Components of E R Model

Entity

Relationship

Constraints

Assumptions

Entity

An entity is an object which can be distinctly identified. For example an entity is simply a person, place, event or thing for which we intend to collect data. If you work for an airline appropriate entities might be pilots, aircraft, routes, suppliers etc.

Relationship

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The relation is the only one data structure used in the relational model to represent both entities and the relationship between them.

Constraints

A constrain is a condition applicable on a field or set of fields.

E.g: Name title must be MR

Assumptions

Typically involve assumptions made about relationship's membership and functionality

Comparison between Different data model structures

Hierarchical

Network

Relational

E R Model

One to many relationship

Easy to use

Database integrity

Data independence

Simplicity

High efficiency

Implementation is complex

Require extra storage

Non hierarchical relations are difficult to map out this model

Many to many relationship

Easier to access

Simplicity in structure

Data access flexibility

The number of line are very high

New queries cannot be implemented

Data independence

Manipulation of data is very easy

Simple and powerful

We can apply mathematical operations on tables

Easier database design, implementation, management and use

Need huge amount of memory

Poor design and implantation is made easy

Simple in structure

User friendly

Good communication

Easy to use

Terms of accessibility representations are restricted

Representations of limited boundaries for relationship

A data can be manipulated but in E R model it cannot be represented

Information loss

Data Mining and Data warehousing

Data mining

It is the process of finding or understanding particular information from large amount data such as database or data warehouse. This process will help the organizations to analyse the information from many angles.

Data Warehousing

It is the place for storing data's for analyse and security purposes. It may be one computer or one big server. Data warehouse is actually use large organizations to find their seasonal trends. The data in the data warehouse will updated regularly.

SYN focused on developments such as data mining and data warehousing like.

Number of departments in SYN

Number of employees in SYN

Number of orders in SYN

Number of suppliers for SYN

Number items in SYN

If the company SYN use the techniques like data warehousing and data mining they can analyse their trends for a particular time and they can come with a detailed report. They could identify like their earnings up to date, how many orders made till, how many suppliers, progress of employees, which supplier is very good in work, which department is running very smoothly etc. For that they have to update their data's in database in regular base.

Different approaches to database design

File Based approach

In 1950's when the use of computers was just starting, data was stored in files and the storage medium was magnetic tape. A file system used to create, get it back and manipulate the files in file system. Traditionally a large organization like hospital would have different files for different purpose like, such as one for patient details, another for storing the medicine details etc. These each files would be used independently to produce reports. These types of files have several disadvantages

In file management system the same data is repeat in many files. For example the details of patient will repeated in doctor's notes and medicine area. This is waste of space. When the same data fields (name, address, tel no) must be changed in different files, some files may be missed. In file management system different programmers create files in different formats.

Database Approach

The database system is essentially a computerized record keeping system. A database management system consists of a collection of interrelated data and a set of program to excess those data. The database management system reduces the duplication of data to a large extend. It avoids the inconsistency of data. Data stored in the database can be shared among several users. It provides security to the information inside a database. So the data can be protected against accidental or intentional modification by unauthorized person.

Database management system is a package that allows the users to define data items, place these items in specified records, combine these records into designated files and then manipulate and retrieve the stored data to fulfill the user's requirements. The typical file processing system has a number of disadvantages. The permanent records are stored in various files and different application programs are written to extract records and to add records to appropriate files. Before the advent of DBMS, organizations typically stored information using such systems. The typical file processing systems has a number of disadvantages. The main disadvantages of file systems are data redundancy, inconsistency, difficult to access data etc. To overcome these disadvantages database is used.

Components of Database environment

Database

The main component of DBMS is the database itself. Database is an organized collection of information. The database consists of structures to hold this information.

Data Definition Language (DDL)

A database schema is specified by a set of definitions expressed by a special language called data definition language (DDL), which is a language used to specify overall design of the database. The result of compilation of DDL statement is a set of tables that are stored in a special file called data dictionary or data directory. It is a file that contains data about data.

The main function of DDL

It specifies the proper data type

It specifies the length of data item

It specifies different constraints for the attribute in a table

It may specify privacy lock for preventing, accessing, data in an unauthorized user.

It gives unique name to each data item in the table

It specifies the relationship of data in a table

It may define the range of values that a data item can assume.

Data Manipulation Language (DML)

A data manipulation language is the language that allows users to access, edit and change the data by the appropriate model. Manipulation of data would include addition, modification and removal of data from the table. Data manipulation includes the following different process.

Insertion: It is the process of adding new information into a database.

Deletion: The process in which removal of information from a table is called deletion.

Retrieval: The process in which access and process the data form a database is called retrieval.

Modification: The process in which change the data in a database is called modification.

There are two different types of DML used, they are

Procedure DML

In this Procedure DML the user need to specify what data are needed and the user also need to specify how to get those data.

Non procedural DML

In this Non procedural DML the user need to specify what data are needed but not need to specify how to get those data. Non Procedural DML are usually easier to learn and used than procedural DMLs.

Users

Users interact with the DBMS indirectly via application programs or directly via simple query languages. The user's interactions with the DBMS include the definition of logical relationships in the database and manipulation of data.

Different types of Database Users

One who uses database is called database user. There are four different types of database users. The different types of database users are differentiated by the way in which users interact with the system. The main four database users are,

Database administrator

Application programmer

Native user

Sophisticated user

Database administrator

The entire database needs a central control of both data and the program that access those data. The person who has such central control over the system is called data base administrator (DBA). The main functions of DBA are schema definition, providing security, etc.

Application programmers

A person who interacts with the system through application programs is called application programmers. Application programmers are computer programmers who write different application program. Application programmers write programs in C, C++, Visual Basic and Pascal and these programs also include some DML commands for manipulating database.

Native users

Native users are database users who interact with the system by invoking one of the permanent application programs that has been written previously.

Sophisticated users

These users interact with the system through any type of query language .These types of users interact with system without writing program.