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Articles by Alex Onsman
Page 14 of 15
Comparison between E-R Model and Object Oriented Model
The detailed comparison on the E- R model and Object Oriented Model is given as follows −E-R ModelER model is used to represent real life scenarios as entities. The properties of these entities are their attributes in the ER diagram and their connections are shown in the form of relationships. An ER model is generally considered as a top down approach in data designing.An example of ER model is −Advantages of E - R modelThe data requirements are easily understandable using an E - R model as it utilises clear diagrams.The E-R model can be easily converted into a relational database.The ...
Read MoreRepresentation of class hierarchy in DBMS
Class hierarchy can be viewed one of two waysSpecialization (Top Down Approach)Generalization (Bottom Up Approach)SpecializationSpecialization is a process of identifying subsets of an entity that shares different characteristics. It breaks an entity into multiple entities from higher level (super class) to lower level (subclass). The class vehicle can be specialized into Car, Truck and Motorcycle ( Top Down Approach)Hence, vehicle is the superclass and Car, Truck, Motorcycle are subclasses. All three of these inherit attributes from vehicle. Moreover, these three share those attributes among themselves while containing some other attributes which make them different.GeneralizationGeneralization is a process of generalizing an entity which ...
Read MoreMoving Object Databases
Moving objects are those whose position changes frequently over a period of time. Conventional databases don't know how to handle this scenario, as they assume the data objects are stationaryIn this case, we use moving object databases. These databases can store information about moving objects and allow querying on them.For example- The location of nearest taxis for a particular customer can be found using querying on moving object databases.The approaches used in handling moving object databases are:Location ManagementThe current locations of the objects are saved in the database and estimations are made on their near future positions. This information is ...
Read MoreMandatory and optional Participation
Mandatory and optional participation are observed in E-R models between 2 different entities.Mandatory ParticipationIn the mandatory participation, for every instance of entity A, there must exist an instance of entity B and vice versa.An example of Mandatory participation would be relationship between mother and child. The child entity would exist only if there were a mother and similarly a mother would exist only if there were a childOptional participationIn optional participation, it is not necessary for all the instances of the entity to participate in a relationship. It may be that the number of instances participating for a particular entity ...
Read MoreBootstrap 4 .border-secondary class
Use the border-secondary class in Bootstrap 4 to add a gray border to an element.Set the border as − Gray border I have styled our element as shown in the following code snippet − .test { width: 200px; height: 150px; margin: 10px; } You can try to run the following code to implement the border-secondary class −ExampleLive Demo Bootstrap Example .test { width: 200px; height: 150px; margin: 10px; } Rectangle Gray border
Read MoreData and structural independence
Structural IndependenceStructural independence exists when changes in the database structure do not affect DBMS ability to access data.Structural dependence exists when changes in the database structure do not affect DBMS ability to access data.Data IndependenceThe changes done in the lower level will not affect the upper layers. The two types are −Physical Data IndependenceLogical Data IndependenceLet us begin with Physical Data Independence −Physical Data IndependenceModify physical schema without affecting the schema or logical data. It is easier to achieve.It is achieved by the internal level of the database and mapping from the logical level to the internal level. The Conceptual Schema ...
Read MoreFourth Normal Form (4NF)
What is 4NF?The 4NF comes after 1NF, 2NF, 3NF, and Boyce-Codd Normal Form. It was introduced by Ronald Fagin in 1977.To be in 4NF, a relation should be in Bouce-Codd Normal Form and may not contain more than one multi-valued attribute.ExampleLet us see an example −Movie_NameShooting_LocationListingMovieOneUKComedyMovieOneUKThrillerMovieTwoAustraliaActionMovieTwoAustraliaCrimeMovieThreeIndiaDramaThe above is not in 4NF, sinceMore than one movie can have the same listingMany shooting locations can have the same movieLet us convert the above table in 4NF −Movie_NameShooting_LocationMovieOneUKMovieOneUKMovieTwoAustraliaMovieTwoAustraliaMovieThreeIndiaMovie_NameListingMovieOneComedyMovieOneThrillerMovieTwoActionMovieTwoCrimeMovieThreeDramaNow the violation is removed and the tables are in 4NF.
Read MoreTransitive dependency in DBMS
What is Transitive DependencyWhen an indirect relationship causes functional dependency it is called Transitive Dependency.If P -> Q and Q -> R is true, then P-> R is a transitive dependency.To achieve 3NF, eliminate the Transitive Dependency.ExampleMovie_IDListing_IDListing_TypeDVD_Price ($)M08L09Crime180M03L05Drama250M05L09Crime180The above table is not in 3NF because it has a transitive functional dependency −Movie_ID -> Listing_IDListing_ID -> Listing_TypeTherefore, the following has transitive functional dependency.Movie_ID -> Listing_TypeThe above states the relation violates the 3rd Normal Form (3NF).To remove the violation, you need to split the tables and remove the transitive functional dependency.Movie_IDListing_IDDVD_Price ($)M08L09180M03L05250M05L09180Listing_IDListing_TypeL09CrimeL05DramaL09CrimeNow the above relation is in Third Normal Form (3NF) ...
Read MoreData Dictionary in DBMS
Data Dictionary consists of database metadata. It has records about objects in the database.What Data Dictionary consists ofData Dictionary consists of the following information −Name of the tables in the databaseConstraints of a table i.e. keys, relationships, etc.Columns of the tables that related to each otherOwner of the tableLast accessed information of the objectLast updated information of the objectAn example of Data Dictionary can be personal details of a student −ExampleStudent_IDStudent_NameStudent_AddressStudent_CityThe following is the data dictionary for the above fields −Types of Data DictionaryHere are the two types of data dictionary −Active Data DictionaryThe DBMS software manages the active data ...
Read MoreHow to normalize a Database Table
Normalization removes data redundancy and update, insert and delete anomalies and gives you a normalized perfect database design that a database administrator love.To normalize a database table, follow the below given steps that highlights the role of normalization forms and its uses −First Normal Form (1NF)1 INF is useful in removing the data redundancy issue and anomalies of a database. All attributes in 1NF should have atomic domains.Second Normal Form (2NF)The Second Normal Form eliminates partial dependencies on primary keys.Third Normal Form (3NF)The Third Normal Form eliminates Transitive Functional Dependency.Fourth Normal Form (4NF)To be in 4NF, a relation should may ...
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