"Sister school to teach database system" (d) the concept of database design

hello Hello everyone, today we learn the concept of database design. Sister school to teach database, never seen such a cool title, right? "Language does not startle," Yes, the title is so cool.

My little sister buried 18-year-old campus goddess of existence, the outstanding universal sport, personality gentle and virtuous. However, only I know, everybody's eyes shining little buried in the past is a hamster dressed in cloak, rolling on the floor, ate and slept and play super house women. And all this change, since the day is night.

Since then, the small underground often let me help her homework. Today she wanted to understand the concept of database design. This tutorial by the way I buried with little dialogue to talk about the concept of database design.

Blog continues to update, the other blog to see the same series. Welcome to my column "sister school to teach database system," I hope we can pay attention to me, and together learn database system.

Small buried: "ER diagram how to paint it."

Entity - relationship model (ER model)

Associated with the contact of the concept

1. Contact, contact type, contact set

• contact:
• Contact type: Contact the same class have in common type
• Contact type of degree
• Contact set: a collection of the current instance of the database stored contact type

2. Contact type ER diagram
   
   

• An entity type can participate in and own the same type of contact
  

Contact-type constraints

1. Contact-type constraints

• Base ratio
• 1 pairs
• Many to many

2. Dependency constraints / engagement constraint: Characterization entities involved in the minimum cardinality type contact type (i.e. a minimum of physical contact to participate in several)

• 0 (partially involved): ER represented as a single line in FIG.
• ≥1 months (all involved): expressed as double the figure in the ER
  
  

Contact type of property

1. Contact type can have attributes. In the ER diagram, with straight lines of contact type and contact type of properties together.
   
2. Weak entity, weak entity set

• Weak entity type
• Identify the entity type
• Contact type logo
• Key part
  
• FIG ER is expressed as follows:
  

3. Multiple Relation

• Multiple Relation (higher-degreerelationships): more than three entities involved contact

• And a n-contact on the n contact Significance of the Dual indicated generally different
  

Small buried: "Enhanced ER model is simple to talk about it, I want to go out."

Enhanced ER model

1. Subclass / superclass

• Disjoint subclasses
• Overlapping subclasses