✅ After sorting out the notes for the questions...
Article directory
● The teaching materials we use:
1. Multiple-choice and fill-in-the-blank questions
- The tasks in the logical design phase include designing views and forming the external schema of the database. ( )
A. Right
B. Wrong
Answer: A. Parsed as follows:
- In an ER diagram, attributes can be related to other entities. ( )
A. Right
B. Wrong
Answer: B. Attributes can only be linked to their corresponding entity type.
- In the demand analysis stage, the actual requirements of users should be investigated, and the focus of the investigation is "data" and "_____".
Answer: processing. The original words in the book.
- A data dictionary is the main outcome of detailed data collection and data analysis. It is about the description of the data in the database, that is, ___ the data, not the data itself.
Answer: Yuan. The original words in the book.
- The connection between two entity types is divided into the following three types: one-to-one connection; one-to-many connection; many-to-____ connection.
Answer: one.
- The data dictionary consists of _____, _____, _____, _____, and _____ sections.
Answer: data item, data structure, data flow, data storage, process. The original words in the book.
- There are three main types of conflicts between the ER diagrams of the subsystems: _____, _____, _____.
Answer: Attribute conflicts, naming conflicts, structure conflicts. The original words in the book.
- There are many interest groups organized in the school. Students can sign up to join multiple groups. Each group has an instructor. Each teacher can guide multiple groups. If students, interest groups, and teachers are regarded as three types of entities, then the guidance There is a ( ) relationship between the teacher and the students.
A. 1:n
B. n:1
C. m:n
D. None of the above is correct
Answer: C. There may be m teachers teaching n students in p groups (m≤p).
- In ER diagrams, attributes of entities are represented by oval boxes. ( )
A. Right
B. Wrong
Answer: A. Entity types are represented by rectangles. Attributes are represented by ovals, and relationships are represented by diamonds.
- The logical structure design is independent of the specific database management system. ( )
A. Right
B. Wrong
Answer: B. It can only be said that the logical structure is an information structure independent of any kind of data model. As for "logical structure design", it cannot be independent of the specific database management system.
- Indexing is a task in the logical structure design phase of the database design process. ( )
A. Right
B. Wrong
Answer: B. It should be the stage of physical structure design.
- In database design, the process of converting ER diagrams into relational data models belongs to the ( ) stage.
A. Requirements analysis
B. Logical design
C. Conceptual design
D. Physical design
Answer: B.
- When there are 5 entities in an ER model, one 1:1 relationship, two 1:M relationships, and one M:N relationship, then according to the rules for converting the ER model into a relational model, the number of converted relational models The number is ( ).
A. 6
B. 7
C. 8
D. 9
Answer: A. An entity type needs to be converted to a relational schema. And for "1:1 relationship", it can be merged with the relationship mode corresponding to any end, and for "1:n relationship", it can be merged with the relationship mode corresponding to the n end. And for "m:n relationship", it can only be converted to a relational schema. For these knowledge points, it is recommended to read the "Complete Version of Introduction to Database Systems - P50" . "P46, P47, P49, P50" is a whole, it is recommended to read it together. If you can’t understand it once, read it twice if you don’t understand it once, and slow down, especially P47, P49, and P50.
- Which of the following statements about indexes is wrong ( ).
A. DBMS creates an index for the primary key by default
B. Use "DROP INDEX" to revoke the index
C. Index creation belongs to the logical model
D. Indexes can improve the speed of query operations
Answer: C. Index creation belongs to the physical model.
- The data implementation phase includes two important tasks, one is data loading, and the other is application coding and debugging. （）
A. Right
B. Wrong
Answer: A. The original words in the book.
- The results of the logical design of the database are not unique. （）
A. Right
B. Wrong
Answer: A. The original words in the book.
- Database management systems generally provide multiple access methods. The commonly used access methods are ______ and ______.
Answer: index method, clustering method.
Two, big questions
- Various competitions are set up in the school track and field meeting. Each competition category has attributes such as category number, category name, and supervisor. Each competition category contains many competition items; each competition item has an item number, item name, competition time and level. and other attributes; each team has attributes such as group number, group name, and team leader. Each delegation consists of multiple athletes, and athletes have attributes such as number, name, age, and gender; each athlete can participate in multiple competitions. There are also multiple athletes participating in each competition event, and athletes participating in the competition have performance attributes.
(1) Draw the ER diagram according to the above semantics,
(2) Convert the ER diagram into a relational schema, and point out the primary key and external key of each relational schema, with an underline representing the primary key and a wavy line representing the external key.
◆ Supplementary Note: An entity type needs to be converted into a relational model. And for "1:1 relationship", it can be merged with the relationship mode corresponding to any end, and for "1:n relationship", it can be merged with the relationship mode corresponding to the n end. And for "m:n relationship", it can only be converted to a relational schema. For these knowledge points, it is recommended to read the "Complete Version of Introduction to Database Systems - P50" .
"P46, P47, P49, P50" is a whole, it is recommended to read it together. If you can’t understand it once, read it twice if you don’t understand it once, and slow down, especially P47, P49, and P50. After you understand it, you can solve these problems easily .
3. Feelings after writing
● Teacher Wang Shan said: "Database is a course with strong practicality. I hope that students will practice more on the actual database system after class, so that they can really master it."
● This chapter is more conceptual, but the main line is still very clear: requirements analysis→conceptual structure design→logical structure design→physical structure design→database implementation and maintenance. At different stages, the focus of the work is different, as shown in the figure below:
● If it is not enough, welcome to leave a message in the comment area for discussion.
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