diff --git a/Course.java b/Course.java
new file mode 100644
index 0000000..fdaf5da
--- /dev/null
+++ b/Course.java
@@ -0,0 +1,90 @@
+package basic;
+
+/**
+ * 课程类，与学科建立多对一关系
+ */
+public class Course {
+    private int id;
+    private String name;
+    private int credit;
+    
+    // 所属学科（多对一关系）
+    private Subject subject;
+    
+    // 先修课程（一门课程可能有多门先修课程）
+    private java.util.List<Course> prerequisiteCourses;
+    
+    public Course(int id, String name, int credit) {
+        this.id = id;
+        this.name = name;
+        this.credit = credit;
+        this.prerequisiteCourses = new java.util.ArrayList<>();
+    }
+    
+    // 添加先修课程
+    public void addPrerequisiteCourse(Course course) {
+        if (course != null) {
+            prerequisiteCourses.add(course);
+        }
+    }
+    
+    // 移除先修课程
+    public void removePrerequisiteCourse(Course course) {
+        if (course != null) {
+            prerequisiteCourses.remove(course);
+        }
+    }
+    
+    // 设置学科
+    public void setSubject(Subject subject) {
+        this.subject = subject;
+    }
+    
+    // Getters and Setters
+    public int getId() {
+        return id;
+    }
+    
+    public void setId(int id) {
+        this.id = id;
+    }
+    
+    public String getName() {
+        return name;
+    }
+    
+    public void setName(String name) {
+        this.name = name;
+    }
+    
+    public int getCredit() {
+        return credit;
+    }
+    
+    public void setCredit(int credit) {
+        this.credit = credit;
+    }
+    
+    public Subject getSubject() {
+        return subject;
+    }
+    
+    public java.util.List<Course> getPrerequisiteCourses() {
+        return prerequisiteCourses;
+    }
+    
+    public void setPrerequisiteCourses(java.util.List<Course> prerequisiteCourses) {
+        this.prerequisiteCourses = prerequisiteCourses;
+    }
+    
+    @Override
+    public String toString() {
+        return "Course{" +
+                "id=" + id +
+                ", name='" + name + '\'' +
+                ", credit=" + credit +
+                ", subject=" + (subject != null ? subject.getName() : "null") +
+                ", prerequisites.size()=" + prerequisiteCourses.size() +
+                '}';
+    }
+}
\ No newline at end of file
diff --git a/Grade.java b/Grade.java
new file mode 100644
index 0000000..7a702c6
--- /dev/null
+++ b/Grade.java
@@ -0,0 +1,55 @@
+package basic;
+
+/**
+ * 成绩类，实现学生与成绩的一对多关联关系，同时与课程建立多对一关系
+ */
+public class Grade {
+    private int id;
+    private double score;
+    
+    // 所属学生（多对一关系）
+    private Student student;
+    
+    // 所属课程（多对一关系）
+    private Course course;
+    
+    public Grade(int id, Course course, double score) {
+        this.id = id;
+        this.course = course;
+        this.score = score;
+    }
+    
+    // 设置学生
+    public void setStudent(Student student) {
+        this.student = student;
+    }
+    
+    // Getters and Setters
+    public int getId() {
+        return id;
+    }
+    
+    public void setId(int id) {
+        this.id = id;
+    }
+    
+    public double getScore() {
+        return score;
+    }
+    
+    public void setScore(double score) {
+        this.score = score;
+    }
+    
+    public Student getStudent() {
+        return student;
+    }
+    
+    public Course getCourse() {
+        return course;
+    }
+    
+    public void setCourse(Course course) {
+        this.course = course;
+    }
+}
\ No newline at end of file
diff --git a/Student.java b/Student.java
new file mode 100644
index 0000000..08d6f47
--- /dev/null
+++ b/Student.java
@@ -0,0 +1,68 @@
+package basic;
+
+/**
+ * 学生类，添加成绩属性并实现学生与成绩的一对多关联关系
+ */
+public class Student {
+    private int id;
+    private String name;
+    private advanced.Parent parent;
+    
+    // 学生的所有成绩（一对多关系）
+    private java.util.List<Grade> grades;
+    
+    public Student(int id, String name) {
+        this.id = id;
+        this.name = name;
+        this.grades = new java.util.ArrayList<>();
+    }
+    
+    // 添加成绩
+    public void addGrade(Grade grade) {
+        grades.add(grade);
+    }
+    
+    // 移除成绩
+    public void removeGrade(Grade grade) {
+        grades.remove(grade);
+    }
+    
+    // Getters and Setters
+    public int getId() {
+        return id;
+    }
+    
+    public void setId(int id) {
+        this.id = id;
+    }
+    
+    public String getName() {
+        return name;
+    }
+    
+    public void setName(String name) {
+        this.name = name;
+    }
+    
+    public java.util.List<Grade> getGrades() {
+        return new java.util.ArrayList<>(grades);
+    }
+    
+    public advanced.Parent getParent() {
+        return parent;
+    }
+    
+    public void setParent(advanced.Parent parent) {
+        this.parent = parent;
+    }
+    
+    @Override
+    public String toString() {
+        return "Student{" +
+                "id=" + id +
+                ", name='" + name + '\'' +
+                ", parent=" + (parent != null ? parent.getName() : "null") +
+                ", grades.size()=" + grades.size() +
+                '}';
+    }
+}
\ No newline at end of file
diff --git a/Subject.java b/Subject.java
new file mode 100644
index 0000000..9015bb3
--- /dev/null
+++ b/Subject.java
@@ -0,0 +1,49 @@
+package basic;
+
+/**
+ * 学科类，实现学科与课程的一对多关联关系
+ */
+public class Subject {
+    private int id;
+    private String name;
+    
+    // 该学科下的所有课程（一对多关系）
+    private java.util.List<Course> courses;
+    
+    public Subject(int id, String name) {
+        this.id = id;
+        this.name = name;
+        this.courses = new java.util.ArrayList<>();
+    }
+    
+    // 添加课程
+    public void addCourse(Course course) {
+        courses.add(course);
+    }
+    
+    // 移除课程
+    public void removeCourse(Course course) {
+        courses.remove(course);
+    }
+    
+    // Getters and Setters
+    public int getId() {
+        return id;
+    }
+    
+    public void setId(int id) {
+        this.id = id;
+    }
+    
+    public String getName() {
+        return name;
+    }
+    
+    public void setName(String name) {
+        this.name = name;
+    }
+    
+    public java.util.List<Course> getCourses() {
+        return new java.util.ArrayList<>(courses);
+    }
+}
\ No newline at end of file