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Database Articles
Page 184 of 546
Entity Integrity Rule in RDBMS
For Entity Integrity Rule, each table has a Primary Key.Primary Key cannot have NULL value.Student_IDStudent_AwardsStudent_AwardsAbove, you can see our primary key is Student_ID. We cannot consider Student_Awards as the primary key since not every student would have received the award.Let us see another example −Employee_IDEmployee_NameEmployee_AgeEmployee_LocationIn the above table, the Primary Key is Employee_IDLet us now summarize the Entity Integrity Rule −Make sure that each tuple in a table is unique.Every table mush has a primary key, for example, Student_ID for a Student table.Every entity is unique.The relations Primary Key must have unique values for each row.Primary Key cannot have NULL ...
Read MoreHow to identify entity from a given problem
Entity in DBMS can be a real-world object with an existence. To identify entity from a given problem, follow the below given tips −Under the problem description, try to find the entity.Search for nouns, like Teacher, Doctor, etc.Classify nouns to get a wider picture about the entities.Read the problem description repeatedly.Entities are like Persons, Students, Teachers, Courses.Entities has attributes, that properties describing it, for example, for Professor entity, the attributes are Professor_Name, Professor_Address, Professor_Salary, etcFor example, Problem DescriptionHospital has doctors and patients. Patients visit the hospital to get a consultation from the doctor. Doctor may suggest tests to examine the condition ...
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 ...
Read MoreFifth Normal Form (5NF)
The 5NF (Fifth Normal Form) is also known as project-join normal form. A relation is in Fifth Normal Form (5NF), if it is in 4NF, and won’t have lossless decomposition into smaller tables.You can also consider that a relation is in 5NF, if the candidate key implies every join dependency in it.ExampleThe below relation violates the Fifth Normal Form (5NF) of Normalization −EmpNameEmpSkillsEmpJob (Assigned Work)DavidJavaE145JohnJavaScriptE146JamiejQueryE146EmmaJavaE147The above relation can be decomposed into the following three tables; therefore, it is not in 5NF −EmpNameEmpSkillsDavidJavaJohnJavaScriptJamiejQueryEmmaJavaThe following is the relation that displays the jobs assigned to each employee −EmpNameEmpJobDavidE145JohnE146JamieE146EmmaE147Here is the skills that are ...
Read MoreObjectives of a good Database Design
Good Database Design is what everyone wants to achieve to avoid the consequences of dealing with a bad design.The following are the objectives of a good database design −Avoid Redundant DataThe table in the database should be constructed following standards and with utmost dedication. It should have different fields and minimize redundant data. The table should always have a Primary Key that would be a unique id.Faultless InformationThe database should follow the standards and conventions and provide meaningful information useful to the organization.Data IntegrityIntegrity assists in guaranteeing that the values are valid and faultless. Data Integrity is set to tables, ...
Read MoreOne-to-One Relationship in DBMS
Relationships in DBMS can be stated as a relation between two entities like Employee-Department, Student-Course, etc.One-to-One relationship in DBMS is a relationship between an instance of an entity with another.The relation can be stated as −An Employee is issued an Employee ID Card. An individual employee is offered a unique ID card in the company. Here, Employee and ID Card (ID_Card) are entities.
Read MoreMajor Concerns with Database Design
Database Design can be a tiresome task and you would need to follow the below approach and tackle the challenges to get a well-designed database.The concerns and challenges with Database design are the following −Following Design StandardsConsidering Design Standards while designing a database is quite essential. It gives you components that are well defined. With this, you can also easily evaluate an existing design.If you are unable to follow the design standards approach, then do not expect the design to be proper and you will not be able to evaluate it.Achieving High Processing SpeedEveryone needs faster access for the relationships ...
Read MoreFully-functional dependency in DBMS
An attribute is fully functional dependent on another attribute, if it is Functionally Dependent on that attribute and not on any of its proper subset.For example, an attribute Q is fully functional dependent on another attribute P, if it is Functionally Dependent on P and not on any of the proper subset of P.Let us see an example −ProjectIDProjectCost00110000015000EmpIDProjectIDDaysE099001320E056002190The above relations states that −Days are the number of days spent on the project.EmpID, ProjectID, ProjectCost -> DaysHowever, it is not fully functional dependent.Whereas the subset {EmpID, ProjectID} can easily determine the {Days} spent on the project by the employee.This summarizes ...
Read MoreThe benefits of good Database Design
A good database design has many benefits and is a goal to achieve for every DBA −Easy Retrieval of InformationIf the design is developed properly, then it would be easier to retrieve information. Correct design means the tables, constraints, and relationships created are flawless.Easier ModificationChanges that you make to the value of a given field will not adversely affect the values of other fields within the table.Easy to MaintainThe database structure should be easy to maintain. The design is perfect if changes in one field is not affecting changes in another field.InformationWith a good design, you can enhance the quality ...
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