DBS Concepts and Architecture

Question 1

Data Model

Answer 1

• A set of concepts to describe the structure of a database

* Has constraints that the database should obey

Question 2

Data Model Operations

Answer 2

• Specify database retrievals and updates

* Basic operations and user-defined operations

Question 3

Conceptual (high-level, semantic) data models

Answer 3

• Provide concepts that are close to the way many users perceive data. (Also called entity-based or object-based data models.)

Question 4

Physical (low-level, internal) data models

Answer 4

• Provide concepts that describe details of how data is stored in the computer.

Question 5

Representational (implementation) data models

Answer 5

• Provide concepts that fall between the above two, balancing user views with some computer storage details.

Question 6

Database Schema

Answer 6

The description of a database.

• Describe the structure and constraints.

Question 7

Schema Diagram

Answer 7

A diagrammatic display of (some aspects of) a database schema.

Question 8

Schema Construct

Answer 8

A component of the schema (e.g., STUDENT, COURSE).

Question 9

Database State

Answer 9

Content of a database at a moment in time.

Question 10

Initial Database State

Answer 10

Refers to the database when it is loaded.

Question 11

Distinction between DB Schema and DB State

Answer 11

• The database schema changes very infrequently. The database state changes every time the database is updated.
• Schema is also called intension, whereas state is called extension.

Question 12

Three Schema Architecture

Answer 12

Defines DBMS schemas at 3 levels:
1, External schemas at the external level describe the various user views usually uses the same data model as the conceptual level
2, Conceptual schema at the conceptual level describe the structure and constraints for the whole database uses a conceptual or an implementation data model
3. Internal schema at the internal level describe physical storage structures and access paths typically uses a physical data model

Question 13

Data Independence (2)

Answer 13

1. Logical Data Independence: Can change the conceptual schema without changing the external schemas and their application programs.
2. Physical Data Independence: Can change the internal schema without changing the conceptual schema.

Question 14

DBMS Languages (3)

Answer 14

1. Data Definition Language (DDL): To specify the conceptual schema of a database.
2. Storage definition language (SDL)
3. View definition language (VDL)
   (last 2 used to define internal and external schemas)
4. Data Manipulation Language (DML): Used to specify database retrievals and updates
5. High Level or Declarative Languages: Specify what to do (what data to retrieve); not how to do. (Ex. SQL)
6. Low Level or Procedural Languages: Specify how to do; not what to do. (Has constructs like loops)

Question 15

Different Interfaces

Answer 15

• Menu-based, popular for browsing on the web
• Forms-based, designed for naïve users
• Graphics-based (Point and Click, Drag and Drop etc.)
• Natural language: requests in written English
• Combinations of the above