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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 ... Read More
Many-to-Many relationship in DBMS is a relationship between more than one instance of an entity with more than one instance of another entity i.e. both the entities can have many relationships between each other.The relation can be stated as −Let us see an example −Many Authors can write a Book, whereas an Author has written more than one book.Here, Book and Author are entities.Let’s say a book has two authors, whereas an individual author has written six books till now.
Database Design Methodologies has phases to guide the designer for assistance. The Methodology has a structured approach to help in the design process.The following are the phases/ models −Conceptual PhaseThe Conceptual phase lets you know the entities and the relation between them. It describes the conceptual schema. The entities & relations are defined here.Logical PhaseLogical data model provides details about the data to the physical phase. The physical process gives ER Diagram, data dictionary, schema, etc that acts as a source for the physical design process.Physical PhaseThe physical database design allows the designer to decide on how the database will ... Read More
To set flex items to be of equal width column, use the flex-fill class. The class displays the items as equal width. In the below example screenshot, you can see that we have four flex items with equal width columns −The flex-fill class is used for every flex items and in this way, we can set equal width. Below, we have two flex items − Example 1 Example 2 ExampleLive DemoThe following is an example showing how to set flex items into equal width columns using the flex-fill class − Bootstrap Example ... Read More
The history of data models had three generations of DBMS −Hierarchical System was the first generation of DBMS. The first generation also came with the CODASYL system. Both of them introduced in 1960s.The second generation includes the Relational Model. Dr. E.F.Codd introduced it in 1970.The third generation includes Object-Relational DBMS and Object-Oriented DBMS.The history timeline of databases is shown below −File based systemsFile based systems came in 1960s and was widely used. It stores information and organize it into storage devices like a hard disk, a CD-ROM, USB, SSD, floppy disk, etc.Relational ModelRelational Model introduced by E.F.Codd in 1969. The ... Read More
Entity in DBMS can be a real-world object with an existence, For example, in a Company database, the entities can be Employees, Department, Project, etc. In a College database, the entities are Profession, Students, Result, Activities, etc.An entity is represented as a single rectangle, shown belowThe following are the entity relationships −One-to-One RelationshipUnder One-to-One (1:1) relationship, an instance of entity P is related to instance of entity Q and an instance of entity Q is related to instance of entity P.Let us see an example −A person can have only one passport, and a passport is assigned to a single person.One-to-Many RelationshipUnder ... Read More
Identifying entity relationships in DBMS is used to identify a relationship between strong and weak entity.Before beginning, let us take an example of Professor entity, which is our Strong Entity, with Professor_ID as a Primary Key −Professor_IDProfessor_NameProfessor_CityProfessor_SalaryThe weak entity is Professor_Dependents entity:NameDOBRelationNow, let us continue, Weak EntityWeak Entity is dependent on Strong Entity and does not have a primary key. Weak Entity has a partial key. It is represented as double rectangle −Strong EntityOther entities are dependent on Strong Entity and it has a key attribute i.e. a primary key and represented as a single rectangle.Identifying RelationshipsIt links the strong and weak entity ... Read More
The HTML DOM Input Email required property determines whether Input Email is compulsory to set or not.SyntaxFollowing is the syntax −Returning boolean value - true/falseinputEmailObject.requiredSetting required to booleanValueinputEmailObject.required = booleanValueBoolean valuesHere, “booleanValue” can be the following −booleanValueDetailstrueIt is compulsory to set the email field to submit form.falseIt is the default value and to set an email field is not compulsory.ExampleLet us see an example of Input Email required property − Live Demo Input Email required form { width:70%; margin: 0 auto; text-align: center; } * { ... Read More
Managing data was the key and was essential. Therefore, data model originated to solve the file system issues. Here are the Data Models in DBMS −Hierarchical ModelIn Hierarchical Model, a hierarchical relation is formed by collection of relations and forms a tree-like structure.The relationship can be defined in the form of parent child type.One of the first and most popular Hierarchical Model is Information Management System (IMS), developed by IBM.ExampleThe hierarchy shows an Employee can be an Intern, on Contract or Full- Time. Sub-levels show that Full-Time Employee can be hired as a Writer, Senior Writer or Editor:AdvantagesThe design of ... Read More
DFS visits the child vertices before visiting the sibling vertices; that is, it traverses the depth of any particular path before exploring its breadth. A stack (often the program's call stack via recursion) is generally used when implementing the algorithm.Following is how a DFS works −Visit the adjacent unvisited vertex. Mark it as visited. Display it. Push it in a stack.If no adjacent vertex is found, pop up a vertex from the stack. (It will pop up all the vertices from the stack, which do not have adjacent vertices.)Repeat Rule 1 and Rule 2 until the stack is empty.Let us ... Read More