Optical fiber cables are transparent, flexible fibers made up of glass or plastic through which light waves can pass. A bunch of fiber optic cables is shown in the following diagram −Structure of a Fiber – Optic CableA cross section of a fiber optic cable reveals three parts −Core −  It is the innermost portion of an optical fiber through which light propagates. It is cylindrical in shape and it made up of a flexible glass of high refractive index. The diameter of the core of a single mode fiber is 8 – 10 μm while multimode fibers are 50 ... Read More

In fiber optic communication, signals are transmitted through an optical fiber. This is based upon certain characteristics of light, namely refraction and total internal reflection.RefractionWhen a light ray goes from a denser transmission medium to a rarer one or vice versa, then its direction changes at the interface of the two medium. This phenomenon is called refraction of light.The density of an optical medium is measured in refractive index. Higher the refractive index, denser it is.The angle between the incident ray and the normal is called angle of incidence Θi, while the angle between the refracted ray and the normal ... Read More

In fiber optic communication, data is transmitted from the source to the destination by sending light pulses through optical fibers. It changes electrical pulses to light signals and vice versa for communication. Fiber optic communications are preferred when a huge amount of data needs to be transmitted across large distances.The process of communication using fiber optics has the following steps −Conversion of input electrical data to light signals : The data to be sent by the sender is in the form of electrical signals. These signals are converted to light pulses by the transmitter circuitry using a light source. A ... Read More

Multidimensional databases are used mostly for OLAP (online analytical processing) and data warehousing. They can be used to show multiple dimensions of data to users .A multidimensional database is created from multiple relational databases. While relational databases allow users to access data in the form of queries, the multidimensional databases allow users to ask analytical questions related to business or market trends.The multidimensional databases uses MOLAP (multidimensional online analytical processing) to access its data. They allow the users to quickly get answers to their requests by generating and analysing the data rather quickly.The data in multidimensional databases is stored in ... Read More

Mobile databases are separate from the main database and can easily be transported to various places. Even though they are not connected to the main database, they can still communicate with the database to share and exchange data.The mobile database includes the following components −The main system database that stores all the data and is linked to the mobile database.The mobile database that allows users to view information even while on the move. It shares information with the main database.The device that uses the mobile database to access data. This device can be a mobile phone, laptop etc.A communication link ... Read More

There may be times when the SQL query was expecting some data type but it got another. In that case type conversion is done by SQL. This is implicit type conversion. However, sometimes the programmer explicitly converts one data type into another in a query. This is known as explicit type conversion. Both of these in detail are given as follows:Implicit Data Type ConversionIn implicit data type conversion, the SQL programmer does not specify anything. Rather the system converts one type of data to another as per its requirements. For example - a numeric data type can be converted to ... Read More

Mathematical functions are very important in SQL to implement different mathematical concepts in queries.Some of the the major mathematical functions in SQL are as follows −ABS(X)This function returns the absolute value of X. For example −Select abs(-6);This returns 6.MOD(X, Y)The variable X is divided by Y and their remainder is returned. For example −Select mod(9, 5);This returns 4.SIGN(X)This method returns 1 if X is positive, -1 if it is negative and 0 if the value of X is 0. For example −Select sign(10);This returns 1.FLOOR(X)This returns the largest integer value that is either less than X or equal to it. ... Read More

The date and time functions in DBMS are quite useful to manipulate and store values related to date and time.The different date and time functions are as follows −ADDDATE(DATE, DAYS)The numbers of days in integer form (DAYS) is added to the specified date. This is the value returned by the function. For example −sql> SELECT ADDDATE('2018-08-01', 31); +---------------------------------------------------------+ | DATE_ADD('2018-08-01', INTERVAL 31 DAY)                 | +---------------------------------------------------------+ | 2018-09-01                                             | +---------------------------------------------------------+ 1 ... Read More

The select statement is used to get the required data from the database according to the conditions, if any. This data is returned in the form of a table.The basic syntax of the select statement is −Select column 1, column 2 ... column N From table_nameAn example of the select statement is −Student_NumberStudent_NameStudent_PhoneStudent_MarksStudent_MajorSubject1Andrew661592728495Literature2Sara658365486565Maths3Harry464756746348Literature4Sally653783708430Literature5Anne745733773288MathsQuery −Select Student_Name From StudentThis query yields the following result −Student_NameAndrewSaraHarrySallyAnneClauses in Select statementThe example of select statement given above is quite simple and not that useful in practice. So, there are many other clauses associated with select statement that make it more meaningful. Some of these are ... Read More

The different types of keys in DBMS are −Candidate Key - The candidate keys in a table are defined as the set of keys that is minimal and can uniquely identify any data row in the table.Primary Key - The primary key is selected from one of the candidate keys and becomes the identifying key of a table. It can uniquely identify any data row of the table.Super Key - Super Key is the superset of primary key. The super key contains a set of attributes, including the primary key, which can uniquely identify any data row in the table.Composite Key -  If ... Read More