Ch.4
Information System Project
- System Design
📌 Database Design
1️⃣ Definition of Database ( DB )
- Database
: A self-describing collection of integrated data.
2️⃣ Characteristics of DB
- Real-time Accessibility
- Continues Evolution
- Concurrent Sharing
- Content Reference
3️⃣ Sources of DB
- Entity
: 자료수집의 대상 - Attributes
: Entity 의 속성 - Relationship
: Entity 간 관계 ( = Table, = File ) - Record
: Field ( Attribute ) 집합체 ( 자료검색단위 ) - Table ( file )
: Record 집합체 ( 자료저장단위 )
📌 Database Management System
1️⃣ Definition of Data Modeling
- Data Modeling
: 현실 세계를 DBMS가 지원하는 논리적 Data 구조로 변환시키는 과정
2️⃣ E-R ( Entity-Relationship ) Modeling
-
Notation of E-R Modeling
▪️ Data entities
▪️ Relationships
▪️ Attributes -
E-R Diagram
: A logical, graphical representation of the entities, associations, data elements for an organization or business.
3️⃣ Sources of E-R Diagram
-
Entity
: A person, place, object, event or concept in the user environment about which the organization wishes to maintain data. -
Entity Type
: A collection of entities that share common properties or characteristics. -
Attribute
: A named property or characteristic of entity. -
Candidate keys
: Attribute that uniquely identifies each instance of an entity type. -
Identifiers
: A candidate key that has been selected.
Selection Rules for an Identifier
▪️ Choose a candidate key that will not change its value.
▪️ Choose a candidate key that will never be null.
▪️ Avoid using intelligent keys.
▪️ Consider substituting single value surrogate keys for large composite keys.
-
Relationship
: An association between the instances of one or more entity types.▪️ Always labeled with verb phrases.
-
Degree
: The number of entity types that participate in a relationship. -
Cardinality
: The number of instances of entity B that can be associated with each instance of entity A.▪️ Minimum Cardinality
: The minimum number of instances of entity B that may be associated with each instance of entity A.▪️ Maximum Cardinality
: The maximum number of instances of entity B that may be associated with each instance of entity A.
4️⃣ Transforming E-R Diagrams into Relations
- Represent Entities
▪️ The value of the key must uniquely identify every row in the relation.
▪️ The key should be nonredundant.
⬇️ E-R Diagram
⬇️ Relation
-
Represent Relationships
ⓐ Binary 1:N Relationships
✅ The key of parent relation must be placed in the child relation.
⬇️ E-R Diagram - 1:N
⬇️ Relation - 1:N
ⓑ Binary or Unary 1:1 Relationships
✅ Needs Foreign key either way
⬇️ E-R Diagram - 1:1
⬇️ Relation - 1:1
ⓒ Binary and Higher M:N Relationships
✅ Intersection Relation 작성 필요 : Stu-Class ( class-ID, student-ID )
✅ The key for intersection relation is always the combination of parent keys.
⬇️ E-R Diagram - M:N
⬇️ Relation - M:N
