Database Fundamentals and Applications Post-Course Exercise Answers
Chapter Exercise Answers
I. Multiple Choice Questions
, Data Definition, Data Manipulation
, File System Stage, Database System Stage
, Attribute, Field, Tuple, Record
, attribute, attribute-to-domain mapping
, relation, relationship
, projection p>
, selection operation, projection operation
, concatenation operation, natural concatenation
Three, Short Answer Questions
, A. A database (
) is a system for storing data over a long period of time.
) is a collection of shared data that is stored in a computer for a long period of time, is organized, and can be represented in a variety of forms
, abbreviated as
, is a computer system software, which has the function of
effectively organizing and storing data,
acquiring and managing data, and
accepting and managing data.
Accepting and fulfilling various requests from users to access data.
A database system is a computer system supported by database technology,
which can realize organized,
dynamic storage of a large amount of
relevant data, and provide data processing and information resource sharing services.
A database system is a system after the introduction of a database into a computer system,
generally consisting of a database,
database management system
its development tools)
, an application system, database administrators and users.
, A: A relation is a two-dimensional table, each with a relation name. In a computer, a relation can be stored as a
, a relation is a table file.
A tuple is a horizontally oriented row, sometimes called a record, in a two-dimensional table.
Attributes are vertically oriented columns in a two-dimensional table, sometimes called a field.
Answer: a database system consists of four parts: the hardware system, the system software, the database application, and the various personnel.
, A: Commonly used data models are hierarchical, mesh and relational.
Hierarchical models are characterized by:
Shaped like an upside-down tree,
there is one and only one node without a parent,
this node is called the root node
and the other nodes have one and only one parent.
The mesh model is characterized by being
shaped like a net,
allowing more than one node to have no parent node,
and a node can have more than one
The relational model is characterized by the following:
In a relationship,
the logical structure of the data is a two-dimensional table.
The table satisfies that the component in each column is
the same type of data;
the order of the columns can be arbitrary;
the order of the rows can be arbitrary;
the components in the table are the smallest items of data that cannot be subdivided
i.e., there are no sub-tables permitted in the table; and any two rows in the table cannot be identical.
Hierarchical models describe data with one-to-many hierarchical relationships in a very natural,
mesh models mainly describe
data with many-to-many relationships.
The relational model has a strict mathematical theory as the basis,
in describing the data using simple and flexible
activity, data independence and other characteristics, and is recognized as the ideal way of organizing data.
, A: No, only a two-dimensional table with the following requirements is said to be a relation:
) The components in each column are data of the same type;
) The columns’ order can be arbitrary;
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1 Basic Concepts of Database Systems
Data: actually symbolic records that describe things.
Characteristics of data: it has a certain structure, there are types and values, such as integer, real, character, etc.. And the value of the data gives the value in line with the stereotype, such as the integer value 15.
Database: is a collection of data, with a unified structure and stored in a unified storage medium, is the integration of a variety of application data, and can be shared by various applications.
Database storage data is stored according to the data provided by the data model, has the integration and sharing characteristics.
Database management system: a system software, responsible for data organization, data manipulation, data maintenance, control and protection and data services in the database, is the core of the database.
2Data integrity is divided into three types, namely, entity integrity, referential integrity, and user-defined integrity.
3Stored in the system database architecture is the basic information that creates the database