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The storage, organization, management, and retrieval of data is controlled by a set of software programs in a database In A DBMS. DBMS's are classified depending upon their data structures or kinds/types. It includes acceptance of data from an application program and instructing the operating system for transferring the required data .Using DBMS information systems can be organized more adequately as the organization's information requirements change. New categories of data can be added to the database without causing any disturbance to the existing system.
Data base is not an invention of modern era. They have been in use since the beginning of the electronic era. Here a brief history of evolution of data base management system is enlisted:
The very first commercial DBMS was born in 1964; IDS - Integrated Data Store, at General Electric, based upon an early network data model developed by C.W.Bachman (Bachman 1965).
"They store and manipulate information and display information in a format and helps in exchanging information via email and over the Internet."
In the era when brown tuxedo jackets ,large glasses were used to be worn by the computer scientists, data was stored in 'flat files'. Flat files are actually the text documents containing data separated by comma's or tabs..The most popular format is Comma Separated Values (CSV) and is broadly supported by different software and operating systems.
This example illustrates view of a flat file .The data separated by comma's would easily be understood by any program which would read this file. In order to reach the category of the 'Database Design Tutorial' it would read file line by line until it reaches 'Database Design Tutorial' and then would read the next word after the comma.
Available and versatile:
It can be create and saved data in any operating system's file system.Text data which is stored in flat files could be read by a wide range of software programs, such as word processors or spreadsheets.
Easy to handle and use:
No need to install any database software .Simply,create a file and data is stored with statements in PHP script.
Data is stored by using less disk space than databases.
Usage of Flat files in the modern age:
Flat files are still in use. Microsoft Excel is one of the most popular application which can handle and acess CSV files. Such data stored in a flat file can be read by a computer program. Programmers use flat files and flat file databases more frequently as compared to the average computer user when constructing applications in DBMS such as MySQL. Website developers also use flat files for use within languages for utilizing PHP or ASP.
The major disadvantage is searching a record takes a long time which lead to the introduction of the concept of indexing.
Updating a record:
In order to merge data of two flat files, relevant information is need to be copied and pasted from one file to another. There is no automation between flat files. Let two or more such flat files contain customers' addresses, for example, a customer moved, manually data need to be modified in each .Changing the information in one file has effect on other files.
All these drawbacks led to the introduction of the Hierarchical Database System.
HIERARICHICAL DATABASE SYSTEM:
In the Mid of 1960s Rockwell did partnership with IBM in order to create information Management System (IMS), IMS DB/DC which lead to the mainframe database market in 1970's and early 1980's.
It is Based on binary trees. It is represented by an upside down tree,showing one-to many relationship between the parent and the child records.
The drawback of accessing and sorting records in FMS was removed by the intro of parent-child relationship in the records in a database. The origin of the data is called the root from where several branches originate having data stored at different levels and the last level is known as the leaf.
Efficient searching of the stored data
Less redundant data
Independence of the data
Security and integrity of Database
Implementation is very complex.
Facing Difficulty in managing data, any modification or alteration is when made to the structure ,the whole structure needs to be get altered which made the task a tedious one. Lack of standards facing problem to add or emptying nodes and difficulty in handling many-many relationships.
Lacking structural independence, such as add up application programming and involves complexity.
In order to avoid this next system took its origin which is called as the Network Database System.
NETWORK DATABASE SYSTEM:
In Early 1960's, Charles Bachmann developed the first DBMS at Honeywell, Integrated Data Store ( IDS)
It was later standardized in 1971 by the CODASYL group (Conference on Data Systems Languages)
It is based on the idea of a Directed acyclic graph having nodes and edgesIn a network model, we can have multiple parents and children records,which then collectively form a generalized graphical structure.
This property is applied at two levels:
It allows modeling of relationships between entities
It Identify 3 database components:
Network schema database organization
Subschema views of database per user
Data management language at low level and procedural
Each record can have multiple parents:
Composed of sets relationships, a set represents a one to many relationship between the owner and the member
Each set has owner andmember record
Members may have several owners
An efficient access-path is offered to its data which is capable to represent almost any informational structure of simple types e.g.
This task is accomplished employing different techniques of mapping mechanisms which are called sets. A set is such a container of pointers which identify sets of data that can be reached from the present record. Three sets are defined by the CODASYL standard - singular/system sets, multimember sets and recursive sets. By Using such such sets, the database designer and the programmer may represent and navigate on 1:1, 1:N and N:M relationships .
This approach is more flexible than the hierarchical approach, but still the programmer needs to know to acess the data in the physical representation form and accordingly applications employing a network database which has to be changed almost every time the structure of database changes.
Difficult to handle System complexity
Difficulty in maintaining and design
Lackness of structural independence
The relational database model was developed by Ted. Codd at IBM's San Jose Lab in 1970.
Two major projects operational in late 1970s were:
INGRES at University of California,
Berkeley became commercial and followed up POSTGRES which was incorporated into Informix.
System R at IBM san Jose Lab,
It later evolved into DB2, and became one of the first DBMS product based on the relational model
In 1976's the Entity-relationship(ER) model was defined byPeter Chen
In 1980's relational based DBMS were developed ,SQL standard was adopted by ISO and ANSI.
Data is stored in separate tables instead of placing all data collectively in a single large table .The design of the records is organized in the form of a set of tables (with unique identifiers) representing both the data and relationships. The fields for matching index speeds up the process and data can be retrieved and manipulated in a variety of ways without the need to assemble or reorganize the original database records
It allows files to relate by means of some common field. to relate any two such files, a common field is required ,making the model extremely flexible.
Uniqueness of each Row
Same Kind of column Values
The Insignificant Sequence of Columns
The Insignificant Sequence of Rows
Unique Name of each column
Usage in the modern age:
This model is now widely used for the efficient organization of data. Today, a wide variety of RDBM products are available, ranging from light-weight desktop applications to feature-packed server systems having highly optimized retrieval methods.
Some of the best known RDBMS are enlilisted :
Microsoft SQL server.
Offers no support for the complex objects such as videos,documents,images,etc
Offers poor support for storing complex objects.
Not efficient and effective integrated support for things like searching of text withen fields.
OBJECT ORIENTED DATABASE MODEL:
Object-oriented DBMS (OODBMS) was developed in 1985
objects are stored rather than data such as integers, strings or real numbers.Object oriented languages are used such as C++, Java, Smalltalk, and others. Objects basically consist of the following properties:
Attributes - data defining the characteristics of object. It may either be simple such as integers, strings or real numbers or a complex object.
Methods - defining the behavior of an object
Therefore objects contain both executable code and data.
How Data is Stored?
Two basic methods are adopted for storing :
Each object possess a unique ID which is defined as a derived class of a base class, using inheritance to determine attributes.
Use of Virtual memory mapping for object storage and management.
Speedy and efficient.
Objects having Many to many relationship are accessed by pointers.
Use of programming techniques with small procedural differences without effecting the whole system.
Late binding may slow speed of acess.
Less user tools exist for OODBMS.
Standards for OODBMS are less stable