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Articles by Bhanu Priya
Page 72 of 106
Explain join dependency in DBMS
Join dependency is a constraint which is similar to functional dependency or multivalued dependency. It is satisfied if and only if the relation concerned is the join of a certain number of projections. Such type of constraint is called join dependency.Let's consider a special class of join dependencies which help to capture data dependencies present in a hierarchical data structure.Example 1The above hierarchical organization informs regarding ward and patients currently admitted to a ward depend only on the hospital but not the facilities present in that hospital. Since hospitals have multiple wards, functional dependencies are not adequate to describe the ...
Read MoreCreate an example table that is in its first normal form(DBMS)
If a table has data redundancy and is not properly normalized then it will be difficult to handle and update. If a relation contains composite or multivalued attributes it violates the first normal form.A table is in 1Nf if the following conditions exist −There are only single valued attributes.Attribute domain does not change.There is a unique name for every attribute or column.The order in which data is stored does not matter.ExampleConsider the table given below −IdNameCourse1AC1, C22EC33BC2, C3The above table is in un normalized form, the course attribute is having multivalued attributes which violates 1NF.Now we represent the above table ...
Read MoreWhich normal form is the highest that satisfies the functional dependencies(DBMS)?
Let's take the dependencies F= {AB->CDEF, AF->ED, F->B} which ONE of the following is the highest normal form that a table R=ABCDEF could satisfy.Select any one from the following −No normal form would be satisfied.Boyce-Codd Normal Form1st Normal Form2nd Normal Form3rd Normal FormGiven Functional dependencies of F are as follows −AB ---> CDEFAF ---> EDF ---> BNow in R.H.S (Right Hand Side) of Functional dependencies of F, attributes B, C, D, E, F are all present but attribute A is missing. So, attribute A must be the part of Super Key.We have to find the closure of A (A+), A+ ...
Read MoreExplain how normal forms can be transformed from lower to higher(DBMS)
In the database management system there are several rules to manage the tables and do the changes like insertion, deletion, updatation and there are different stages at which the tables are organized and these stages are known as normal forms.It is a standard structure of relational databases in which a relation may be inserted in another relation.Five normal formsThere are five normal forms which are explained below −First normal formThe first normal form defines the definition of the table. The rules of the first normal form are as follows −Each column must have a single value.Each column has a unique ...
Read MoreWhat is multivalued dependency in DBMS?
Multivalued dependency (MVD) is having the presence of one or more rows in a table. It implies the presence of one or more other rows in that same table. A multivalued dependency prevents fourth normal form. A multivalued dependency involves at least three attributes of a table.It is represented with a symbol "->->" in DBMS.X->Y relates one value of X to one value of Y.X->->Y (read as X multidetermines Y) relates one value of X to many values of Y.A Nontrivial MVD occurs when X->->Y and X->->z where Y and Z are not dependent are independent to each other. Non-trivial ...
Read MoreCheck which FD violates 3NF in a given relation and decompose R into 3NF(DBMS)
A relation is in 3NF when it is in 2NF and there is no transitive dependency or a relation is in 3NF when it is in 2NF and all non-key attributes directly depend on candidate key.Third normal form (3NF) is the third step in normalizing a database and it builds on the first and second normal forms, 1NF and 2NF.3NF states that all column references in referenced data that are not dependent on the primary key should be removed. Another way of putting this is that only foreign key columns should be used to reference another table, and no other ...
Read MoreConstruct an ER diagram for a company in DBMS?
ProblemDraw of ER model for company considering the following constraints −In a company, an employee works on many projects which are controlled by one department.One employee supervises many employees.An employee has one or more dependents.One employee manages one department.SolutionFollow the steps given below to draw an ER model for the company −Step 1 − Identify the entity setsThe entity set has multiple instances in a given business scenario.As per the given constraints the entity sets are as follows:EmployeeDepartmentProjectDependentStep 2 − Identify the attributes for the given entitiesEmployee − The relevant attributes are name, ssn, sex, address, salary.Department − The relevant ...
Read MoreExplain Mapping the ER diagrams with binary and ternary relationships(DBMS)?
It is the relationship between the instances of two different entity types. Two entities will participate in the relationship.ExamplePerson and events are two different entity types which are related by using the relationship called “attends”.Mapping ER diagram with binary relationshipMapping one to many relationshipExampleHere, Create two tables for two entities.Primary key of one side relation is a foreign key for many side relations.One side relation is customer and many side relations is Order.The primary key cutomerID of the customer is a foreign key of order.The equivalent relations for the above ER diagram are as follows −One-one, many-one, many-many can be ...
Read MoreWhat is a composite attribute in DBMS?
The attributes that cannot be divided into sub-parts are called simple attributes. The attributes which can be divided into sub-parts are called composite attributes.ExampleBalance, account number are simple attributesName, address is called composite attributesLet’s consider an example of how to convert Entity Relationship (ER) model of composite attribute to Relational model.Methods for mappingName of relation = Entity set of ER diagramName of column = Attribute of ER diagramExampleIn this example, Name of the relation =studentName of columns=StdID, name, BranchThe equivalent relation for the above ER diagram is −StudentStdIDNameBranchNow apply this technique for Mapping ER diagram with a composite attribute as ...
Read MoreExplain the concept of key attributes with an example in DBMS?
Key is a data item which is used to identify a record or a value used to identify a record in a database is called a key. It helps uniquely to identify an entity from an entity set.Key allows us to identify a set of attributes that make it sufficient to distinguish entities from each other.ExampleAccount number, employee number, customer number are used as key fields because they specifically identify a record stored in a database.Different types of keysThe different types of keys in the database management system (DBMS) are as follows −Primary keySuper keyCandidate keyAlternate keyArtificial keyForeign keyPrimary, super, ...
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