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!
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!
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!
Ordinary cook, multi-functional health pot
The ordinary chef's multi-functional health pot was a 34-centimeter product with a national recommended retail price of 798 yuan. However, the search results provided did not contain detailed information or instructions for the product. Therefore, it was impossible to provide specific information about the ordinary cook's multi-functional health pot.
trivial functional dependence and partial functional dependence
Based on context alone 1. ** Ordinary Function Dependence ** - In a database, let R(U) be a relation pattern on a set of attributes U, and X and Y be a set of attributes U. If Y is a sub-set of X (that is, Y X), then X→Y is a trivial functional dependence. - For example, in the relationship mode of students (student number, name, gender),{student number, name}→{name} is a trivial functional dependence, because the name itself is a part of {student number, name}. Semantically speaking, trivial functional dependence represented an obviously established dependence relationship. This dependence relationship did not actually contain much meaningful new information, because it only indicated that the dependence of a set of attributes on its own set must exist. 2. ** Part of Function Dependence ** - Let (X,Y) be the property set of the relation pattern (R). If (X→Y) exists a proper set of (X ') such that (X'→Y), then (Y) is partially dependent on (X). - For example, in the Relational Mode course selection (student number, course number, grades, course name),{student number, course number}→{course name}, but in fact,{course number}→{course name}, which meant that the course name only depended on the student number and the course number in the course number, not the entire {student number, course number}, so the course name was partially dependent on {student number, course number}. Partial functional dependence may cause data redundancy-like problems. In the standardized design of a database, it is usually necessary to eliminate partial functional dependence to achieve a higher standard. The Extraordinary Ordinary Life novel is equally exciting. Everyone is welcome to click and read it!
There are only ordinary posts, no ordinary jobs
This sentence emphasized that even if the position seemed ordinary, the work itself was important and should not be underestimated. From many perspectives, every job, no matter how ordinary, had its value. In the field of education, the provincial education conference had made clear many directions for education development, from strengthening the construction of teachers, increasing investment in education, paying attention to education fairness to emphasizing education reform and innovation. Every link could not be separated from the efforts of the education workers in ordinary posts. Although every educational worker had an ordinary position, their work was related to the hope of countless families, the rejuvenation of the nation, and social progress. In the Hangfa Real Estate Administration Center, the discipline officer Wang Junchao showed meticulous service in his ordinary post, from providing wheelchairs for the elderly with mobility difficulties to assisting in business. Although his work was ordinary, it was full of meaning. The entire Hangfa Real Estate team also practiced the service spirit in ordinary posts and played the role of a state-owned enterprise. Like the people who stuck to their posts during the National Day, the cleaner Xue Yuanxia cleaned carefully, the volunteers of the Culture and Travel Bureau Wang Gang and his colleagues patiently provided volunteer services to tourists, and the traffic police were on duty to deal with emergencies. They were engaged in seemingly ordinary jobs in ordinary posts, but they were all performing their duties with a positive attitude and creating unique value in their respective posts. That was why even though the position might be ordinary, every job was extraordinary. The Extraordinary Ordinary Life novel is equally exciting. Everyone is welcome to click and read it!