Database Question Urgent!!!!

First: you are lazy and push everything to someone else.

Second: There are no bonus points for your question.

Third: this question is too retarded.

So, there shouldn't be anyone.

Note: The following answers are collections.

Q: The following software is not part of the database management system A: UNIX

Q: DBS is a computer system that uses database technology. A DBS is an aggregate that includes databases, computer hardware, software, and

A: Database administrators.

Q: For a specific database application, the following statements are true A: None of the above three are unique.

Q: The following are not part of the database system

A: Database Administrator (DBA).

Q: Which of the following four statements is incorrect

A: The database avoids all data duplication.

Q: Not a database system's advantage over a document management system.

A: The access speed is fast.

Q: Among the following four items, the ones that do not belong to the characteristics of relational databases are A: Good data sharing.

Q: Based on the characteristics of the data model --- relational model on which the relational data is based, one of the following is correct

Answer: The data is stored in a two-dimensional structure, and duplicate rows are not allowed in the relational table.

Q: The model that uses a tree structure to represent the connections between entities is A: A hierarchical model.

Q: Relational databases are used to represent connections between entities.

Answer: Two-dimensional tables. Dizzy.

The square enclosed by Uncle Zhang is large.

Uncle Guo 21*9=189

It can also be used to form a circle around a larger area of the nursery.

When m=1, y=x, 2-1, and the intersection of the x-axis a(1,0) b(-1,0).

Note that the function of the image folded up on the x-axis is y=-x 2+1(1), which is not true, for example, y=x+b, over the point b, and in this case, it is also over three points: y=x+b is tangent to y=-x 2+1.

2) When b=2, y=x+2

When y=0, x=-2 passes the point c(-2,0).

a(root m,0) b(-root m,0).

Apparently there is a case.

Root number m<-2 m>4

There is another case (m<4) where y=x+2 does not intersect y=-x 2+m, if y=x+2 tangentially solves the equation with y=-x 2+m, and we get x+2=-x 2+m x 2+x+2-m=0 and there is a single root: 1-4(2-m)=0 -7+4m=0 m=7 4, so 0 root number m m 2>m m(m-1)>0 gives m<0 or m>1

So when m>1 there is no intersection point.

So it's not true. There are 2,3 in the correct solution

1. Conceptual design and logical design.

2. Database security and database integrity.

3. One is the loading of data, and the other is the coding and debugging of the application.

4. An entity.

5. Correctness.

6. Timeout method and wait graph method.

7. Data items and data structures.

8. Mode. DBMS: A database management system is a large-scale software that manipulates and manages databases, and is used to establish, use, and maintain databases, abbreviated as DBMS. It manages and controls the database in a unified manner to ensure the security and integrity of the database.

Transitive dependency: In the relational pattern r(u), let x,y,z be different subsets of the attributes of u, if x determines y, y determines z, and x does not contain y,y does not determine x, (x y) z=empty set, then z-transfer function dependency is called transitive functional dependency to x.

Two-segment lock protocol: The so-called two-segment lock protocol means that all transactions must lock and unlock data items in two stages: 1

Before you can read or write any data, you must first apply for and obtain a block on that data, and 2After a block is released, the transaction does not apply for and receive any other blocks. The meaning of the so-called "two-stage" lock is that the transaction is divided into two phases, the first of which is to acquire the block, also known as the expansion phase.

At this stage, the transaction can request any type of lock on any data item, but it cannot release any locks. The second stage is the release of the lockdown, also known as the contraction phase. At this stage, the transaction can release any type of lock on any data item, but can no longer apply for any locks.

Media Failure Recovery Steps: Mount the latest backup copy of the database (the staging copy closest to the time of the failure) to restore the database to the consistent state it was in at the time of the most recent staging. For the database copy of the dynamic dump, the copy of the log file at the start of the dump must also be loaded, and the recovery system failure method (i.e., redo+undo) must be used to restore the database to a consistent state.

Load the appropriate copy of the log file ** save a copy of the log file at the end of the day) and redo the completed transaction. That is, the log files are first scanned to find out the identity of the transaction that was committed at the time of the failure, and it is recorded in the redo queue; The log files are then scanned forward to redo all transactions in the redo queue.

That is, the "updated value" in the log record is written to the database;

aob=120°，∴boc=60°。

oa=ob=4, oc= ob= 4=2, bc=ob?sin60°=

The coordinates of point b are (2,

2) The parabola passes through the origin o and the point, and the parabola can be set to y=ax2+bx, and a(4,0),b( 2, substitution, obtain, solution.

The analytic formula for this parabola is .

If ob=op, then 22+|y|2=42, the solution is y= when y= in RT pod, pdo=90°, sin pod=, pod=60°

POB = POD + AOB = 60° + 120° = 180°, that is, P, O, and B are in the same straight line.

y= does not fit the topic, discard.

The coordinates of the point p are (2,

If ob=pb, then 42+|y+ |2=42, solution y=

The coordinates of the point p are (2,

If op=bp, then 22+|y|2=42+|y+ |2. Solve y=

The coordinates of the point p are (2,

To sum up, there is only one eligible point p, whose coordinates are (2, ).

Database is a warehouse that organizes, stores and manages data according to the data structure, which was born more than 60 years ago, with the development of information technology and the market, especially after the nineties of the twentieth century, data management is no longer just about storing and managing data, but has transformed into a variety of data management methods required by users. There are many types of databases, from the simplest to store all kinds of data, to large database systems that can store massive amounts of data.

Definition 1 database (11 photos).

A database is a warehouse built on a computer storage device to organize, store, and manage data according to the data structure.

To put it simply, it can be regarded as an electronic filing cabinet - a place to store electronic documents, and users can add, intercept, update, delete and other operations on the data in the file.

In the daily work of economic management, it is often necessary to put some relevant data into such a "warehouse" and process it accordingly according to the needs of management.

For example, the personnel department of an enterprise or public institution often stores the basic information of its employees (employee number, name, age, gender, place of origin, salary, resume, etc.) in a table, which can be regarded as a database. There you have this"Data warehouse"We can inquire about the basic situation of an employee at any time as needed, and we can also inquire about the number of employees whose wages are within a certain range, etc. If all this work can be done automatically on the computer, then our personnel management can reach a very high level.

In addition, it is also necessary to establish a large number of such in financial management, warehouse management, and production management"Databases", so that it can use the computer to realize the automatic management of finance, warehouse, and production.

Definition 2Strictly speaking, a database is an organized, shareable collection of data stored in a computer for a long time. The data in the database refers to the data that is organized, described and stored together in a certain data model, with the characteristics of the smallest redundancy, high data independence and easy scalability, and can be shared by multiple users within a certain range.

This kind of data collection has the following characteristics: it is not duplicated as much as possible, it serves a variety of applications of a specific organization in an optimal way, its data structure is independent of the application that uses it, and the addition, deletion, modification and query of data are managed and controlled by unified software. From the perspective of development history, database is an advanced stage of data management, which is developed by document management systems.