Functional dependency in dbms

Functional dependencies are a fundamental concept in database design, and are used to establish relationships between attributes in a database. They are used to ensure that the database is in a state of normalization, which helps to minimize data redundancy and improve data integrity. A Functional dependencies can also be represented using mathematical notation. For example, the functional dependency above can be represented as: Employee ID → Employee Name, Address, etc. It’s important to note that functional dependencies only apply to the individual tuples in the table, and not to the table as a whole. Functional dependencies can be used to identify and eliminate data redundancy in a database. For example, if a database contains a table with the attributes “employee ID” and “employee name”, and another table with the attributes “employee ID” and “employee address”, then there is a functional dependency between “employee ID” and “employee name” in the first table, and between “employee ID” and “employee address” in the second table. By combining these two tables into one, with the attributes “employee ID”, “employee name”, and “employee address”, the data redundancy is eliminated. Functional dependencies can also be used to identify and eliminate data inconsistencies in a database. For example, if a database contains a table with the attributes “employee ID” and “employee name”, and another table with the attributes “employee ID” and “employee address”, then there is a fun...

The relationship existing between any two attributes is called functional dependency. This kind of relationship is present between the non-key attribute and the primary key inside a table. Functional dependencies come in use for designing or redesign of a relational database which assists to remove redundancy (duplication of data), thus minimizing the chance of update anomalies. Redundancy is removed via a process called normalization. xà y In the above illustrated Functional Dependency, x will be known as the determinant and y will be known as the dependent. For Example Let us imagine that there is a table where employee data is the key attributes are: Emp_Name, Emp_ID, Emp_Address. Here Emp_Name attribute can individually identify the Emp_Id attribute of the given table. The reason behind this identification is that if one is aware of the Emp_Name then we can identify the employee ID linked with it. This Functional Dependency can be illustrated as: Emp_Nameà Emp_Id The above illustration implies that Emp_Id is functionally dependant on Emp_Name. Different types of Functional Dependency • Trivial Functional Dependency • Non Trivial Functional Dependency Trivial functional Dependency • xà y will have trivial functional dependency if y is a subset of x. • Following are also Trivial Dependencies: aà y, yà y Example Let us assume there is a table that has two columns Emp_Name and Emp_Id. . Similarly, Emp_Nameà Emp_Name and Emp_Idà Emp_ID also have trivial functional dependenc...

I'm taking a database theory course, and it's not clear to me after doing the reading how I can infer keys, given a set of functional dependencies. I have an example problem: Find all keys of the relation R(ABCDEFG) with functional dependencies AB → C CD → E EF → G FG → E DE → C BC → A Demonstrate your knowledge by identifying which of the following is a key. a. BCDEF b. ADFG c. BDFG d. BCDE Can someone walk me through how I should decompose the functional dependencies to conclude that some combination of attributes is a key? I expect I'll face a number of these types of problems and I need to understand how to approach it. Take an FD, e.g. AB→C Augment until all attributes are mentioned, e.g. ABDEFG → CDEFG (note that this is equivalent to ABDEFG → ABCDEFG because it is trivially true that A->A and B->B). This tells you that ABDEFG is a superkey. Check the other FDs in which the LHS is a subset of your superkey, and that on its RHS contains some other attribute of your superkey. There are two. EF→G and FG→E. Remove the attributes of the RHS of these from your superkey. Doing so gives you two keys, that are certainly superkeys, but not necessarily irreducible ones: ABDEF and ABDFG. However, from AB→C and CD→E we can also derive that ABD→E. Hence we can also remove the E from our ABDEF key. The nasty thing here is that when I said "Check the other FDs", that apparently means that you should also check any FD that appears in the closure of your set of FDs (i.e. any FD that i...

In the field of database management, functional dependency is a crucial concept that helps to maintain the accuracy and consistency of data stored in a database. It is used to establish a relationship between different attributes of a database table, which ensures that the data is stored in an organized and meaningful manner. This article discusses the definition of functional dependency in DBMS, its types, properties, and at last the advantages of functional dependency in DBMS. What is Functional Dependency in DBMS? Functional dependency in DBMS, as name suggests, is a relationship between two or more attributes of a database table related to each other, where the value of one attribute uniquely determines the value of another attribute. For example, let’s consider a database table "Employee" with the following attributes: Employee (Employee_ID, Employee_Name, Address, Salary) In this case, the Employee_ID attribute uniquely identifies each employee. Therefore, we can say that Employee_Name, Address, and Salary are functionally dependent on Employee_ID. We can denote this functional dependency as follows: Employee_ID → Employee_Name, Address, Salary Take another example, suppose we have a database table "Order" with attributes like Order_ID, Product_Name, Quantity, and Price. In this case, the product name is dependent on the order ID, which means that if we know the Order_ID, we can determine the corresponding Product_Name. We can denote this functional dependency as: Or...

11 Chapter 11 Functional Dependencies Adrienne Watt A functional dependency (FD) is a relationship between two attributes, typically between the PK and other non-key attributes within a table. For any relation R, attribute Y is functionally dependent on attribute X (usually the PK), if for every valid instance of X, that value of X uniquely determines the value of Y. This relationship is indicated by the representation below : X ———–> Y The left side of the above FD diagram is called the determinant, and the right side is the dependent. Here are a few examples. In the first example, below, SIN determines Name, Address and Birthdate. Given SIN, we can determine any of the other attributes within the table. ISBN ———–> Title Rules of Functional Dependencies Consider the following table of data r(R) of the relation schema R(ABCDE) shown in Table 11.1. Table 11.1. Functional dependency example, by A. Watt. As you look at this table, ask yourself: What kind of dependencies can we observe among the attributes in Table R? Since the values of A are unique (a1, a2, a3, etc.), it follows from the FD definition that: A → B, A → C, A → D, A → E • It also follows that A →BC (or any other subset of ABCDE). • This can be summarized as A →BCDE. • From our understanding of primary keys, A is a primary key. Since the values of E are always the same (all e1), it follows that: A → E, B → E, C → E, D → E However, we cannot generally summarize the above with ABCD → E because, in general, A → E, ...

For example, in a table listing employee characteristics, including Social Security number (SSN) and name, it can be said that name is dependent upon SSN (or SSN -> name) because an employee's name can be uniquely determined from an SSN. However, the reverse statement (name -> SSN) is not true because more than one employee can have the same name but always have different SSNs. Trivial Functional Dependencies A trivial functional dependency occurs when you describe a functional dependency of an attribute on a collection of attributes that includes the original attribute. For example, -> SSN. This type of functional dependency is called trivial because it can be derived from common sense. It is obvious that if you already know the value of B, then the value of B can be uniquely determined by that knowledge. Full Functional Dependencies A full functional dependency occurs when you already meet the requirements for a functional dependency and the set of attributes on the left side of the functional dependency statement cannot be reduced any further. For example, -> name is a functional dependency, but it is not a Multivalued Dependencies Multivalued dependencies occur when the presence of one or more rows in a table implies the presence of one or more other rows in that same table. For example, imagine a car company that manufactures many models of car, but always makes both red and blue colors of each model. If you have a table that contains the model name, color, and year...