Database Fundamentals

Introduction

The information storage and retrieval has become very important in our day to day life. The old era of manual system is no longer used in most of the places. For example, to book your airline tickets or deposit your money in the bank the database systems may be used. The database system makes most of the operations automated. A very good example for this is the billing system used for the items purchased in a super market. Obviously this is done with the help of database application package. Inventory systems used in a drug store or in a manufacturing industry are some more examples of database. We can add similar kind of examples to this list.

Apart from these traditional database system, more sophisticated database systems are used in the internet where a large amount of information is stored and retrieved with efficient search engines. For instance, http://www.google.com is a famous website that enables users to search for their favorite information on the internet. In a database we can store starting from text data to very complex data like audio, video etc.

Database Management Systems (DBMS)

A database is a collection of related data stored in a standard format, designed to be shared by multiple users. A database is defined as "A collection of interrelated data items that can be processed by one or more application programs".

A database can also be defined as "A collection of persistent data that is used by the application systems of some given enterprise". An enterprise can be a single individual (with a small personal database), or a complete corporation or similar large body (with a large shared database), or anything in between.

Data

Data is the raw material from which useful information is derived. The word data is the plural of Datum. Data is commonly used in both singular and plural forms. It is defined as raw facts or observations. It takes variety of forms, including numeric data, text, audios, videos and images. Data is a collection of facts, which is unorganized but can be made organized into useful information. The term Data and information come across in our daily life and are often interchanged.

Information

Data that have been processed in such a way as to increase the knowledge of the person who uses the data. The term data and information are closely related. Data are raw material resources that are processed into finished information products. The information as data that that has been processed in such way that it can increase the knowledge of the person who uses it.

In practice, the database today may contain either data or information.

Data Processing

The process of converting the facts into meaningful information is known as data processing. Data processing is also known as information processing.

Metadata

Data that describe the properties or characteristics of other data.

Data is only become useful when placed in some context. The primary mechanism for providing context for data is Metadata. Metadata are data that describe the properties or characteristics of other data. Some of these properties include data definition, data structures and rules or constraints. The metadata describes the properties of data but do not include that data.

It allows the database designer and users to understand what data Exit, what the data mean, and what the fine distinctions are between seemingly similar data items. The management of Metadata is at least as a crucial as meaning the associated data since data without clear meaning can be confusing, misinterpreted or erroneous. 

Database System Application

Database are widely used. Here are some representative applications.

1. Banking

For customers information, accounts and loans and banking transactions.

2. Airlines

For reservations and schedule information. Airlines were among the first to use database in a geographically distributed manner - terminals situated around the world access the central database system through phone lines and other data networks.

3. Universities

For student information, course registrations and Results.

4. Credit & Transactions

For purchase on credit cards and generation of monthly statements.

5. Telecommunication 

For keeping records of calls made, generating monthly bills, maintaining balance on prepaid calling cards and storing information about the communication networks.

6. Finance 

For storing information about holdings, sales and purchases of financial instruments such as stocks and bonds.

7. Sales

For customer, product and purchase information.

8. Manufacturing 

For management of supply chain and for tracking production of items in factories, inventories of items in warehouse / stores and orders for items.

9. Human Resources

For information about employees, salaries payroll taxes and benefits, and for generation of paychecks.

Characteristics of the Database Approach

A shared collection of logically related data along with the description of the data that suits to the need of large enterprises.

This unit describes the basic difference between the traditional way of processing, also called as file processing and the database method of processing the data. Every operating system provides users to open, save and close a file. The users can stores appropriate information in these files. Take a look at the image below, which shows the traditional file processing system that stores the program and data description in a file. The related information of a particular application is stored in various files named as File1, File2, etc. and these files are manipulated using Program1, Program2, etc. This is the method that was used in early days.

It means that without a DBMS, the data will simply be dumped into one or more files. For any update, the files need to be opened and manually search for the line or record, update and then save the file. Now you can understand the difficulties involved in marinating this type of information storage.

With the advent of database systems, the file processing approach is no longer used. Now you can observe with the image below that the database is in the disk which in turn is controlled by the DBMS. In this approach the Application program 1 along with its data semantics, Application Program 2 along with its data semantics etc. Interact with the database where the actual data and constraints are stored through the DBMS. The DBMS provides the necessary control and manipulation software modules for these application programs to access the data stored in the database.

This way the applications are free from the system dependent code and achieve program data independence.

Advantages of DBMS

One of the main advantages of using a database management system is that the organization can exert via the DBA, centralized management and control over the data. The database administrator is the focus of the centralized control. If any application requiring a change in the structure of a data record, the DBA makes the necessary modifications, which do not affect other applications or users of the record in question.

The following are the major of advantages of using a Database Management System (DBMS).

1. Reduction of Redundancies

Centralized control of data by the DBA avoids unnecessary duplication of data and effectively reduces the total amount of data storage required. It also eliminates the extra processing necessary to trace the required data in a large mass of data. Another advantage of avoiding duplication is the elimination of the inconsistencies that tend to be present in redundant data files.

2. Data Independence and Efficient Access

Database application programs are independent of the details of auto representation and storage. In addition a DBMS provides efficient storage and retrieval mechanisms, including support for very large files, index structures and query optimization.    

3. Data Integrity

Centralized control can also ensure that adequate checks incorporated in the DBMS to provide data integrity, which means that the data contained in the database is both accurate and consistent. Therefore data values being entered for storage could be checked to ensure that they fall within a specified range and are of the correct format. For example, the value for the age of an employee may be in the range of 16 and 75. Also it should be ensured that if there is a reference to certain object, that object must exist. In the case of automatic teller machine. for example: a user is not allowed to transfer funds from a nonexistent savings account to a checking account.

4. Data Security

Confidential data must be accessed by unauthorized persons. Different levels of security could be implemented for various types of data and operations.

5. Reduced Application Development time

Since the DBMS provides several important functions required by applications, such as concurrency control and crash recovery, high level query facilities etc. Only application - specific code needs to be written.

6. Conflict Resolution

Since the database is under the control of the DBA, he should resolve the conflicting requirements of various users and applications.

The DBA chooses the best file structure and access method to get optimal performance for the response - critical applications, while permitting less critical applications to continue to use the database, through with a relatively slower response.

7. Data Administration 

By providing common base for large collection of data that is shared by several users, a DBMS facilitates maintenance and data administration tasks. A good DBA can effectively ensure the fine tuning, the data representation, periodic backups etc.

8. Concurrent Access and Crash Recovery 

A DBMS supports the notion of a transaction and executes the actions of transactions in an interleaved fashion to obtain good performance, but schedules them in such a way as to ensure that conflicting operations are not permitted to procced concurrently. Further, the DBMS maintains a continuous log of the changes to the data, and if there is a system crash, it can restore the database to a transaction - consistent state. That is, the actions of incomplete transactions are undone. Thus, if each complete transaction, executing alone, maintains the consistent of criteria, then the database state after recovery from a crash consistent.

Disadvantage of DBMS

The disadvantage of DBMS system is overhead cost. The processing overhead introduced by the DBMS to implement security., integrity and sharing of the data causes a degradation of the response and throughput times. An additional cost is that of migration from a traditionally separate application environment to an integrated one.

Even though centralization reduces duplication, the lack of duplication requires that the database be adequately backup sop that in the case of failure the data can be recovered. 

Backup and recovery operations are complex in a DBMS environment, and this is an increment in a concurrent multi user database system. A database system requires a certain amount of controlled redundancies and duplication to enable access to related data items.

Centralization also means that the data is accessible from a single source, namely the database. This increases the potential severity of security breaches and disrupting of the operation of the organization because of down times and failures.

Database Architecture

The functional components of a database system can be broadly divided into query processor components and storage manager components. The query processor includes:

1. DML Complier 

It translates DML statements in a query language into low level instructions that the query evaluation engine understands.

2. Embedded DML Pre - compiler 

It converts DML statements embedded in an application program to normal procedure calls in the host language. The pre-complier must interact with the DML compiler to generate the appropriate code.

3. DDL Interpreter 

It interprets DDL Stateline its and records them in a set of tables containing metadata.

4. Transaction Manager

Ensure that the database remains in a consistent (correct) state despite system failures, and that concurrent transaction executions processed without conflicting.

5. File Manager

Manages the allocation of space disk storage and the data structures used to represent information stored on disk.

6. Buffer Manager

It responsible for fetching data from disk storage into main memory and deciding what data to cache in memory.

Also some data structures are required as part of the physical system implementation:

1. Data Files

The data files store the database by itself.

2. Data Dictionary

It stores metadata about the structure of the database, as it is used heavily.

3. Indices

It provides fast access to data items that hold particular values.

4. Statistical Data

It stores statistical information about the data in the database. This information used by the query processor to select efficient ways to execute a query.

Keywords

Data Abstraction

A database management system is a collection of interrelated files and a set of programs that allow users to access and modify these files. A major purpose of a database system is to provide users an abstract view of the data. This is called data abstraction.

Data processing

The process of converting the facts into meaningful information is known as data processing. Data processing is also known as information processing.

Data

Data is the raw material from which useful information is derived.

Database

A shared collection of logically related data along with the description of the data that suits to the needs of large enterprise.

Metadata

Data that describe the properties or characteristics of other data.