Database-Relationship.md

@@ -7,16 +7,22 @@ Their elements are listed as follow:
 - s_selected_course: uses **id** as primary key and **must stay the same as id in s_student**, and stores student_id and course_id at the same time.
 - s_teacher: uses **id** and **sn** as primary key and stores name, password, clazz_id and photo at the same time.
 - s_course: uses **id** as primary key and **must stay the same as id in s_teacher**, and stores name, teacher_id, course_date, selected_num, max_num and info at the same time. 
+
+In the following picture, the red part is the primary key.
 ![Relationship](uploads/9c2bfd6dc06df7887c6845205e5dcb86/Relationship.png)
 
 **Sprint4**
 
-At first we set up a new table: s_attendance. (The turquoise part is the new element, the orange part is new primary key, the turquoise relation line is the new relationline)
+At first we set up a new table: s_attendance. 
 - s_attendance: uses **id** as primary key, and stores course_id, type, student_id and course_date at the same time. Besides, course_id, course_date and student_id **must relatively stay the same as** id in s_course, course_date in s_course and id in s_student.
+
+In the following picture, the turquoise part is the new element, the orange part is new primary key, the turquoise relation line is the new relationline.
 ![Relationship1](uploads/438266a9fc428a9ec9a3b680b450adbe/Relationship1.png)
 
-Then we make some changes to the database. (The turquoise part is the new element and the turquoise relation line is the new relationline)
+Then we make some changes to the database. 
 1. Add the new element date in s_attendance.
 2. course_id in s_selected_course must also **stay the same as** id in s_course
 3. Add the new element count in s_course.
+
+In the following picture, the turquoise part is the new element and the turquoise relation line is the new relationline.
 ![Relationship2](uploads/93bbf3cd173d42cd1cbcbe9e88d56e4a/Relationship2.png)
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