Is a transfer function dependency a full function dependency?

You see that a in this relationship determines some non-principal properties, and e and ea determine other properties, and they are basically different from each other, that is, at least a and e

It's completely possible to detach from two things. Because the main attributes are not the same, and the determination is also different, right, in a high-level relationship, you can't try to put two things in one relationship, if that's the case, then it can only be the 1nf.

When answering the first question, you must not write like above, but write concepts like upstairs. That's what I'm explaining in the vernacular.

2.Decomposition: a, b, c, d) (e, f) (e, a, g).

When it comes to decomposition, it's not something complicated like you wrote. That is, one thing is said within a relation, and there are no transfer function dependencies and partial function dependencies between the gates. It's a one-to-one certainty. Gradually get a little closer to the dependencies with trivial functions.

BCNF paradigm.

If the relational pattern r 1nf, and all functions depend on x->y(y x), and the determinant x contains a candidate code for r, then r is said to belong to the bc paradigm and is denoted as r bcnf.

A relational pattern that satisfies the BCNF paradigm is:

All non-primary properties are fully functionally dependent on each code.

All primary properties are dependent on any set of properties that do not contain any set of properties for each code that does not contain it.

If r bcnf, then r excludes the passing and partial dependency of any attribute on the code.

It doesn't belong.

The transfer function dependency belongs to the relational pattern r(u), in which x, y, and z are different subsets of the properties of u. In the relational pattern r (u), if x y, y z, z are not a subset of y, and y does not determine x, then z is said to be transitive functional dependency.

The definition indicates that there are 2 cases of transfer function dependencies:

1) y x is true, in this case the transfer function dependency degenerates into a partial function dependence, that is, the z part of the function depends on x, and the partial function dependency is a special transfer function dependence. (2) y x is not true, which is a transfer function dependence in the ordinary sense.

In r (u), if x y, y z, y are not a subset of x, and y does not determine x, then z is said to be dependent on the x transfer function. Since it is pointed out that y is not a subset of x, it is denied that some function dependencies are special transfer function dependencies.

The defined transfer function depends on the case in definition 1, so that the proposition "If r 3nf, then r 2nf" cannot be proved to be correct, so that there is no inclusion relationship between various paradigms as shown in Figure 1, and the relational data theory presents locality and inconsistency. So definition 2 is not rigorous.

In r (u), if x y, y z, y are not a subset of x, z is not a subset of y, z is not a subset of x, and y does not function to determine x, then z is said to be dependent on the x transfer function.

Like Definition 2, it points out that y is not a subset of x, denies that some function dependencies are special transfer function dependencies, and also makes the various paradigms not have the inclusion relationship as shown in Figure 1, and the relational data theory presents locality and inconsistency, so it is not rigorous.

Partial function dependency is a mathematical term. In the relational pattern r(u), if x y, and there is a true subset of x0 such that x0 y, then y is said to be dependent on the x part of the function.

Let r(u) be the relational pattern on the attribute set u, and x,y be a subset of u. If for any of the possible relations of rr(u) r, it is impossible for two tuples in r to have equal property values on x, but unequal property values on y, then it is said that "the x function determines y" or "the y function depends on x", which is denoted as x y.

In general, a function dependency can only be determined based on the meaning of the word. For example, the name-age function dependency is only true if there is no homonymite, and if the same name is allowed, the age function no longer depends on the name. Designers can also impose mandatory rules on the real world.

For example, it is not permissible to allow the same name to appear, so that the name age function dependence is established, and if the same name is found, it is refused to be loaded into the tuple, which is generally unreasonable. Functional dependencies do not refer to the constraints that one or some of the relationships of the relational pattern r satisfy. Rather, it refers to the constraints that all relations of r must be satisfied.

For example, the SC (SNO, CNO, GRADE) relationship model assumes that in the current record, each student takes one course, and the fact that each student currently takes only one course does not limit him to only one course, and only when the system stipulates that each person can only take one course, does the above argument really constitute a data dependence.

Attribute relationships on which the function depends:

There are three kinds of relationships between attributes, but not every one of them has a function dependency. Let r(u) be the relational pattern on the attribute set u, and x,y be a subset of u.

1. If there is a 1 1 relationship (one-to-one relationship) between x and y, such as a 1 1 relationship between the school and the principal, then there is a function dependent on x y and y x.

2. If there is a 1 n relationship between x and y (a one-to-many relationship), such as a 1 n relationship between age and name, then there is a function dependence on y x.

3. If there is a m n relationship (many-to-many relationship) between x and y, such as m n relationship between students and the course, there is no functional dependency between x and y.

According to the meaning of the two, the main difference between the two is the different definitions.

Data dependence is an abstraction of the interconnection between attributes in the real world, which is an intrinsic nature of data. In computer science, data dependency refers to a state when a program structure causes the data to reference previously processed data. In compilation, data dependency is a part of data analysis.

A function dependency is when a set of properties determines another set of properties, and when another set of properties is said to depend on that set of properties. Functional dependency is a mathematically derived term that characterizes the dependence of the value of one property or set of attributes on the value of another property or set of attributes. Function dependency is the semantic property of the information expressed by the relationship itself, and cannot be determined by the way the attribute constitutes the relationship, nor can it be determined by the current content of the relationship.

Hello! In r(u), if x y, and for any true subset of x x'

Both have x'y, then y is called a complete function dependence on x, denoted as: x y

If x y, but the incomplete function of y depends on x, then y is said to be dependent on part of x, which is denoted as xy. (Generally, 1:1 is a full function dependency, and m:1 is a partial function dependency) if it is helpful to you, I hope to adopt it.

Part of the function depends on.

The difference between a lai and a full function dependency.

Partial function dependency: If x->y and there is a true subset of x1 such that x1->y is such that y is partially dependent on x.

Full function dependency: If x->y and there is no x1->y for any true subset of x1, then y is said to be completely dependent on x.

Examples: -> at the same time -> or -> are partially dependent.

In r(u), x->y, if any one of x is a true subset x'->y, which is a partial dependency, if x'It is not certain that y is a complete function dependency. For example, (sno,cno)->grade is fully function-dependent, because neither of the SNOs,CNOs can be missing to determine grade

However, if (sno,cno)->sdefpt is partially function-dependent, because sno can be a deterministic sdept,

Function dependence bai is defined from a mathematical point of view, and is used to describe the mutual constraints and interdependence between the attributes of the relationship in the relationship.

Circumstances. Function dependence is common in real life, for example, to describe the relationship of a student, there can be multiple attributes such as student number, name, department, etc., because a student number corresponds to one and only one student, and a student is enrolled in a certain department, so when the value of the "student number" attribute is determined, the values of "name" and "department" are uniquely determined, At this time, it can be said that the "name" and "department" functions depend on the "student number", or the "student number" function determines the "name" and "department". Write as: student number, name, student number, department. The exact definition of function dependencies is given below.

Definition: Let u be a set of attributes, r(u) be a relation on u, and x and y are subsets of u.

If, for any possible relation under r(u), there is a value of x that corresponds to a unique concrete value of y, the y function is said to depend on x, denoted as x y.

where x is called the determining factor. Furthermore, if there is y x, it is said that x and y are interdependent and denoted as x y. For example, in the "system" relationship shown in the table, if the value of the system name is unique, that is, the system name is different, then there is a function dependency set:

Multi-valued dependence: y->-x and x has t[x] and u[x] in layman's terms:

Multi-value dependence"To put it bluntly, it is"Polygamy"A man [y] can have a wife [x], but the wife can be t[x] and u[x], which are two or more people.

Function dependencies"That's it"Monogamy"A man can only have a wife, but it can only be one person, which is understandable from above"Monogamy"The system is also"Polygamy"One of the reasons"Polygamy"You can marry only one wife.

Function dependencies"That's it"Multi-value dependence"Special circumstances.