Is there only ordinary multi-valued dependence in the 4GN?
4. Let me explain it to you in detail. ###Fourth Normal Form (4GN) and Multi-valued Dependence (MVR) In database design, 4HF was a very important model. It required that every non-main attribute in the relationship model could not depend on the non-main attributes of other non-main attributes. In other words, a relationship model should have no multi-valued dependence and no joint dependence. Multi-valued dependence refers to the fact that an attribute in a relationship model depends on multiple values of other non-main attribute sets in the relationship model. ###Ordinary and Non-Ordinary Multivalue Dependences - ** Ordinary multi-valued dependence **: When the set of values of Y is a sub-set of X, that is, Y X, the multi-valued dependence X→→Y is called ordinary. This meant that the value of Y was completely determined by the value of X, regardless of whether there were other attributes in Y. - ** Non-trivial multi-valued dependence **: If Y is not a set of X, that is, Y X, then the multi-valued dependence X→→Y is called non-trivial. In this case, the value of Y not only depended on the value of X, but it might also depend on attributes other than X. ### 4 Multivalue Dependences in HF In 4HF, only trivial multi-valued dependence is allowed. This meant that if there were any non-trivial multi-valued dependence, it would need to be eliminated through the database normalisation process. This usually involves breaking down the relationship model into smaller, more manageable parts to ensure data integrity and integrity. Through the above analysis, we can see that there is a close relationship between 4HF and multi-valued dependence, but there are also obvious differences. I hope this information will help you better understand the concepts of 4HF and multi-valued dependence and their application in database design. The Extraordinary Ordinary Life novel is equally exciting. Everyone is welcome to click and read it!
Ordinary multi-valued dependence example
Let the relation model R(U), U = {A, B, C}, let X = {A}, Y = {B}, Z = {C} and Z = U-X- Y. If for any relation r of R(U), given a pair of (A's value, C's value), there is a set of B's value, and this set of B's value only depends on the value of A and has nothing to do with the value of C. When Z is an empty set (that is, there are only two attribute sets of A and B in the relation pattern), it forms an ordinary multi-valued dependence X→→Y. For example, if there is a relationship that represents the student's course selection, assume that the student can only choose one course.(The situation is simplified here for example), the relationship model has an attribute set {student name, course name, teacher name}. If we only consider the two attribute sets {student name} and {course name}, for each student name, the course name is determined (there is no multi-valued situation, because the setting can only choose one course). At this time, if the other attribute sets are regarded as empty sets (here is the attribute set of teacher name), this can be regarded as an ordinary multi-valued dependence. The Extraordinary Ordinary Life novel is equally exciting. Everyone is welcome to click and read it!
Ordinary, multi-valued dependence and non-ordinary
In a multi-valued dependence, let R(U) be a relation pattern on the property set U, X, Y, and Z be a set of U, and Z = U-X- Y. If X→→Y and Z is an empty set, then X→→Y is called a trivial multi-valued dependence; if Z is not empty, then X→→Y is called a non-trivial multi-valued dependence. For example, in the relationship model <Warehouse Manager, Warehouse No., Warehouse Item No.>(Assuming that a product can only be placed in one warehouse, but a warehouse can have several managers), there is a warehouse number corresponding to a <Warehouse Manager, Warehouse Item No.>, but in fact, this warehouse number is only related to the inventory item number and has nothing to do with the manager. This is a manifestation of multi-value dependence. The Extraordinary Ordinary Life novel is equally exciting. Everyone is welcome to click and read it!
Asymmetrical multi-valued dependence
In the database relationship model, there was an unbalanced situation in the multi-valued dependence. Generally speaking, multi-valued dependence refers to a relationship where one attribute group has a dependence on another attribute group. This relationship is independent of other attributes, does not involve the uniqueness of keys, and is different from functional dependence. For example, in the relationship StudentClasses (StudentID, Course, Instructor), StudentID ->> Course means that the student can take multiple courses (there is a multi-valued dependence between the student and the course). This is an unbalanced relationship because the course cannot determine the student (the unbalanced characteristic), and this dependence is independent of the teacher (the characteristic of multi-valued dependence is independent of other attributes). This kind of non-symmetrical multi-valued dependence was of great significance in the process of database design and regularisation. For example, when detecting multi-valued dependence, it was necessary to analyze this kind of non-symmetrical attribute group relationship and verify whether it met the conditions of multi-valued dependence through a formal definition (for the relationship R and the attribute group A, B, C, if A ->> B, then for each fixed value of A, there is a set of unique B values. These B values and C values are independent) to ensure the accuracy and efficiency of the database design. The Extraordinary Ordinary Life novel is equally exciting. Everyone is welcome to click and read it!
What is the extraordinary multi-valued dependence?
In the relation pattern R(U)(U is the property set), let X, Y, and Z be a set of U, and Z = U-X- Y. If the multi-valued dependence in the relation pattern is true, and the set is not empty, then the multi-valued dependence is called non-trivial. The Extraordinary Ordinary Life novel is equally exciting. Everyone is welcome to click and read it!
What is the extraordinary multi-valued dependence?
If X->->Y, and X, Y, and Z are subsets of U, Z = U-X- Y, then X->->Y is called a non-trivial multi-valued dependence if Z is not empty. For example, in the relationship model, if there is U = warehouse + administrator + item,(warehouse, item) determines a group of administrators, but the administrator is only determined by the warehouse,(R-warehouse-administrator) is not an empty set, here warehouse->-> administrator is a non-trivial multi-valued dependence. The Extraordinary Ordinary Life novel is equally exciting. Everyone is welcome to click and read it!
Ordinary Dependence and Extraordinary Dependence
Ordinary dependence refers to the dependence of a certain attribute set on itself in the relationship. For example, in a set composed of attributes A and B, the dependence of A and B on themselves (A→A and B→B) is trivial dependence. In a table that stores student performance information, the set of attributes {SNo, CNo, Score},{SNo} → SNo,{CNo, Score} → Score, etc. are also trivial dependence. Nontrivial dependence is if X → Y holds and Y does not belong to X. For example, in a student's report card,{SNo, CNo} → Score is a non-trivial dependence because Score does not belong to the combination key {SNo, CNo}. The Extraordinary Ordinary Life novel is equally exciting. Everyone is welcome to click and read it!
Is ordinary dependence the same as extraordinary dependence?
Ordinary dependence was different from extraordinary dependence. A trivial dependence refers to a property or property set that is completely dependent on itself. For example, in the relationship R(A, B), A -> A and B -> B are trivial dependence. The non-ordinary dependence was not the dependence of this attribute collection on oneself. In the process of database normalisation, trivial dependence had no practical effect and would not affect the integrity or integrity of the database design. It was more used to define and identify more complex dependence relationships, such as functional dependence, partial dependence, and transitive dependence. Non-trivial dependence had different effects and meanings in the design of the database. The Extraordinary Ordinary Life novel is equally exciting. Everyone is welcome to click and read it!
The difference between ordinary dependence and extraordinary dependence
Ordinary Dependence referred to the fact that a certain attribute in the attribute set depended on itself and did not need to obtain information from other attributes. For example, in a table containing the property set {SNo, CNo, Score},{SNo} → SNo, {CNo, Score} → Score is a trivial dependence. A non-trivial dependence is a non-trivial dependence if X → Y is true and Y does not belong to X. For example, in the student report,{SNo, CNo} → Score is a non-trivial dependence, because the score Score does not belong to the combination key {SNo, CNo}. In summary, the main difference between the two was that ordinary dependence was the dependence of attributes on themselves, while non-ordinary dependence was the dependence of an attribute (set) on another attribute (set) that did not belong to itself. The Extraordinary Ordinary Life novel is equally exciting. Everyone is welcome to click and read it!
Which of the following is ordinary dependence?
In the database, ordinary dependence referred to the fact that a certain attribute in the attribute set depended on itself and did not need to obtain information from other attributes. For example, in a set of attributes A and B, the dependence of A and B on themselves (A -> A and B -> B) is a trivial dependence. In a table that stores student performance information (containing the attribute set {SNo, CNo, Score}),{SNo} → SNo,{CNo, Score} → Score, etc. are also trivial dependence. In contrast, if X → Y holds and Y does not belong to X, it is called a non-trivial dependence. For example, in a student's report card,{SNo, CNo} → Score is a non-trivial dependence because the Score does not belong to the combination key {SNo, CNo}. The Extraordinary Ordinary Life novel is equally exciting. Everyone is welcome to click and read it!
Explanation of Ordinary Function Dependence Noun
In a relation, let the relation be R(U), and X and Y be a set of attributes on U. If X contains Y, then there must be X→ Y, which is called trivial functional dependence. For example, in employee relationships, the employee number could always determine itself (recorded as "employee number → employee number"), and the attribute set composed of employee number and gender could always determine the employee number or gender attribute (can be recorded as "(employee number, gender) → employee number" and "(employee number, gender) → gender" respectively). These were all trivial functional dependence. Simply put, one attribute (or set of attributes) was completely dependent on another attribute (or set of attributes). This dependence was obvious and direct. The Extraordinary Ordinary Life novel is equally exciting. Everyone is welcome to click and read it!