CH4 Flashcards
Three Stages of Database Development
– Requirements Analysis Stage
– Component Design Stage
– Implementation Stage
Systems Development Life Cycle (SDLC)
- Requirement analysis
- Design
- Development
- Testing
- Maintenance
The Requirements Analysis Stage
– User Interviews – Forms – Reports – Queries – Use Cases – Business Rules
Elements of E-R Models
– Entities
– Attributes
– Identifiers
– Relationships
Entity
• something of importance to a user that needs to be represented in a database • represents one theme or topic • in an entity-relationship model, entities are restricted to things that can be represented by a single table.
Entity Class
a description of the structure and format of the occurrences of the entity
Entity Instance
a specific occurrence of an entity within an entity class
Attributes
- have a data type and properties
* describe the entity’s characteristics
Identifiers
- Entity instances have identifiers
- An identifier will identify a particular
instance in the entity class
Identifier Types
- Uniqueness
- Composite
Uniqueness
– Identifiers may be unique or nonunique.
– If the identifier is unique, the data value for the
identifier must be unique for all instances.
Composite Identifier
- Consists of two or more attributes.
• E.g., OrderNumber & LineItemNumber are both
required.
Relationships
• Entities can be associated with one
another in relationships.
Relationship Degree
• Defines the number of entity classes participating in the relationship: – Degree 2 is a binary relationship. – Degree 3 is a ternary relationship.
1:1 (one-to-one) Binary Relationship
A single entity instance in one entity class is
related to a single entity instance in another
entity class.
• An employee may have no more than one locker;
and
• A locker may only be accessible by one employee
