Lesson 2 Flashcards
is the way in which the data in a database is viewed (or
represented to) by users.
DBMS ARCHITECTURE
ANSI stands for…?
American National Standards
It sets standards for American goods so that they can
be used anywhere in the world without compatibility
problems.
ANSI
Three level ANSI-SPARC Architecture
* External level
* Conceptual level
* Internal level
- the uppermost level in the database.
- known as the view level because it deals with how a user views your database.
- allows a user to access a customized version of the data in your database.
The External Level (User Representation of Data)
- tells how the database was structuredlogically.
- tells about the relationship between the data members of
your database. - It’s actually an overview of yourdatabase.
The Conceptual Level (Holistic Representation of Data)
- the lowest level in a three-tiered database.
- deals with how the stored data on the database is represented to the user
- shows exactly how the data is stored and organized for
access to your system.
The Internal Level (Physical Representation of Data)
- the overall description of thedatabase.
- the skeleton structure that represents the logical view of the entire database.
Database Schema
Three types of Schema:
* External Schema
* Conceptual Schema
* Internal Schema
is at the highest level and is also called subschemas that
correspond to the different viewsof the data.
External Schema
describes all the entities, attributes, and relationships
together with integrityconstraints.
Conceptual Schema
is the complete description of the internal model,
containing the definitions of stored records, the methods of
representation, the data fields, and the indexes and storage structures used.
Internal Schema
- a state of operational database with data at any given
time. - It contains a snapshot of thedatabase.
- It tends to change with time.
- A DBMS ensures that it’s every instance (state)is in a valid
state, by diligently following all the validations,
constraints, and conditions that the database designers
have imposed.
Database Instance
A language that allows the DBA/ users to describe and
name the entities, attributes, and relationships required
for the application, together with any associated integrity
and securityconstraints.
Data Definition Language
A descriptive language that allows the DBA or user to
describe and name the entities required for the
application and the relationships that may exist between
the different entities. Used to specify the database
schema.
Data Definition Language
