Three Schema Architecture and ERD Flashcards
This architecture is proposed to support DBMS characteristics of 1. support for multiple views of data and 2. program-data independence
Three-Schema Architecture
Not explicitly used in commercial DBMS products, but has been useful in explaining database system organization.
Three Schema Architecture
Three Schema Architecture defines DBMS schemas at what three levels?
- Internal schema
- Conceptual schema
- External schema
Schema that describe physical storage structures and access paths and typically uses a physical data model.
Internal Schema
Schema that describe the structure of the whole database for a community of users.
Conceptual schema
Schema that describe various user views that uses conceptual/implementation model.
External schema
Mapping among schema levels are needed to ______________________.
transform requests and data.
Programs refer to an _________ , and are mapped by the DBMS to the internal schema for execution.
external schema
Data extracted from the internal DBMS level is reformatted to match the ___________________________.
Match the user’s external view.
Types of Data Independence
Logical and Physical
The capacity to change the conceptual schema without having to change the external schemas and their associated application programs.
Logical data independence.
The capacity to change the internal schema without having to change the conceptual schema.
Physical Data Independence
Describes data entities, relationships, and attributes.
Entity Relationship Model.
A specific thing or object in the real world with an independent existence.
Entity.
A collection of all entities of a particular entity type in the database at any point in time.
Entity set.
A particular property that describes an entity.
Attribute
Two populator notation in Entity Relationship Diagram.
Chen’s notation (we are using) and Crow’s foot notation.
An association between among several entities.
Relationship
If t wo or more relationships have the same name, they are of the same __________ _______.
Relationship type
Degree of a relationship is the ____________________.
Number of participating entity types.
a relationship type that associates entities which are members of the same entity type.
Recursive Relationship type
_____ must be specified in Recursive relationship type to distinguish the meaning of every participation of the entity type.
Roles
