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A Database is a organized or structured collection of data that is managed to meet the needs of a community of users. Or in other word. Database is a collection of information and programs to access that information.

Foundations of Database Terms

  • File:- A file is an ordered arrangement of records in which each record is stored in a unique identifiable location. In most computer systems, the sequence of records is either alphabetic or numeric based on field common to all records such as name or number.
Records:- A record or tuple is a complete set of related fields. (Tuple is also called raw) For example, the Table 1 below shows a set of related fields, which is a record. In other words, if this were to be a part of a table then we would call it a row of data. Therefore, a row of data is also a record.

  • Fields:- A field is a property or a characteristic that holds some piece of information about an entity. Also, it is a category of information within a set of records. For example, the first names, or address or phone numbers of people listed in address book.
  • Relations:- In the relational data model, the data in a database is organized in relations. A relation is synonymous with a ‘table’. A table consists of columns and rows, which are referred as field and records in DBMS terms, and attributes and tuples in Relational DBMS terms.
  • Attributes:- An attribute is a property or characteristics that hold some information about an entity. A ‘Customer’ for example, has attributes such as a name, and an address

File Organization

File organization is the methodology which is applied to structured computer files. Files contain computer records which can be documents or information which is stored in a certain way for later retrieval. File organization refers primarily to the logical arrangement of data in a file system.

Types of Files:- A file has been defined as a collection of records. In this context there are three main types of files:
  1. Master files:- Master files contain the permanent data of a data-processing system and are kept up to date by applying new data from the transaction files. They represent the most up to date situation of the system. Master files contain two basic types of data:
    1. data of a more or less permanent nature which only requires updating occasionally;
    2. data which will change every time transactions are applied to file.
  2. Transaction files:- These files contain only that data necessary to keep the master files up to date. Data is collected on a daily, weekly or monthly basis into a transaction file which is then used to update the master file
  3. Reference or Lookup files:- These are files that contain data which may need to be looked up during the processing of the master file.

Types of File Organization

The main ways of organizing data in files include:
  1. Serial Organization:- In serial organization, records are held and accessed in a predetermined sequence of keys. Records are held and accesses in numerical, alphabetical or chronological order.
  2. Sequential Organization:- A sequential file contains records organized in the order they were entered. The order of the records is fixed. The records are stored and sorted in physical, contiguous blocks within each block the records are in sequence. Records in these files can only be read or written sequentially.
  3. Indexed Sequential Organization:- In index sequential, records are physically ordered by primary key. And the index gives the physical location of each record. Records can be accessed sequentially or directly, via the index. The index is stored in a file and read into memory at the point when the file is opened
  4. Direct or Random Organization:- Direct access files are stored on magnetic disks or other devices where each record is assigned a physical address. Records in these files or stored on the medium (disk) according to their disk address or their relative position within the file.

Database Management System

A Database Management System (DBMS) is computer software designed for the purpose of managing databases based on a variety of data models. A DBMS is a complex set of software programs that controls the organization, storage, management, and retrieval of data in a database.
Database Model:- Data model is defined as the collection of conceptual tools for describing data, data relationships, data semantics and consistency constraints. There are following four Data Model:-
  • The Hierarchical Data Model:- The hierarchical data model organizes data in a tree structure. There is a hierarchy of parent and child data segments. This structure implies that a record can have repeating information, generally in the child data segments. Data in a series of records, which have a set of field values attached to it. It collects all the instances of a specific record together as a record type. These record types are the equivalent of tables in the relational model, and with the individual records being the equivalent of rows. To create links between these record types, the hierarchical model uses Parent Child Relationships.
  • The Network Model:- The popularity of the network data model coincided with the popularity of the hierarchical data model. Some data were more naturally modeled with more than one parent per child. So, the network model permitted the modeling of many-to-many relationships in data. The basic data modeling construct in the network model is the set construct. A set consists of an owner record type, a set name, and a member record type. A member record type can have that role in more than one set, hence the multi-parent concept is supported.
  • The Relational Model (RDBMS-Relational Database Management System):- A Relational database management system (RDBMS) is a database management system (DBMS) that is based on the relational model as introduced by E. F. Codd. Most popular commercial and open source databases currently in use are based on the relational model. A short definition of an RDBMS may be a DBMS in which data is stored in the form of tables and the relationship among the data is also stored in the form of tables. A table is a collection of records and each record in a table contains the same fields.

Properties of Relational Tables

  • Values Are Atomic
  • Each Row is Unique
  • Column Values Are of the Same Kind
  • The Sequence of Columns is Insignificant
  • The Sequence of Rows is Insignificant
  • Each Column Has a Unique Name
Some of the more popular relational database management systems include: 
  • Sybase
  • Filemaker
  • Microsoft SQL Server
  • MySQL
  • Oracle

Features and Responsibilities of an RDBMS

An RDBMS is software that is used for creating and maintaining a database. Maintaining involves several tasks that an RDBMS takes care of. These tasks are as follow:
  • Control Data Redundancy:- Since data in an RDBMS is spread across several tables, repetition or redundancy is reduced. Redundant data can be extracted and stored in another table, along with a field that is common to both the tables. Data can then be extracted from the two tables by using the common field.
  • Data Abstraction:- This would imply that the RDBMS hides the actual way, in which data is stored, while providing the user with a conceptual representation of the data. 
  • Support for Multiple Users:- A true RDBMS allows effective sharing of data. That is, it ensures that several users can concurrently access the data in the database without affecting the speed of the data access.
In RDBMS different keys are used to access records from the table. Following are the different keys:-
  • Unique key:- It is a field of a table which can not be repeated. 
  • Primary Key:- It is a attribute of a table which can be used to access the record. Primary key should be unique and it should not be null.
  • Foreign key:- If a relation has no primary key then it use primary key of another related table known as foreign key.
  • Candidate key:- Attribute of a given table which has property to become a primary key is called candidate key.

The Object Oriented Model

In object oriented model information is represented in the form of objects as used in object oriented programming. Object Oriented Database Management Systems is a combination of object oriented programming language capabilities and database capabilities. It contains some properties like transparently persisted data, concurrency control, data recovery, associative queries, and other capabilities. Some object oriented programming languages are Java, C++, .NET, Visual Basic, Python etc.

Types of Database Architectures

Following are the three types of database architectures: 
  • Client-Server Database Systems:- A client is defined as a requester of services and a server is defined as the provider of services. Today centralized systems act as server systems that satisfy requests generated by client systems. Functionally database systems can be broadly divided into two parts:
    • Front end: front end of a database system consists of tools such as SQL user interface, forms interfaces, reports generation tools, and analysis tools.  
    • Back end: The back end of a database system manages query evaluation and optimization, access structures, concurrency control and recovery management.
  • Distributed Systems:- Distributed database is a collection of multiple logically interrelated databases distributed over a computer network and a distributed database management system is a software system that manages a distributed database while making the distribution transparent to the user. Transparency means hiding the details of where the data is physically stored within the system.
    Reasons for building a distributed database are sharing of data, autonomy, and availability.
Functions of distributed databases:
  1. Keeping track of data.
  2. Query Processing by a communication network.
  3. Security Management.
  4. Distributed Transaction Management
  5. Database Recovery.

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