Week 2 Flashcards
ANSI-SPARC Three-Level Architecture
External
Conceptual
Internal
Users’ view of the database.
Describes that part of database that is relevant to a particular user.
External level
Community view of the database.
Describes what data is stored in database and relationships among the data.
Conceptual level
Community view of the database.
Describes what data is stored in database and relationships among the data.
Internal level
Objectives of Three-Level Architecture
All users should be able to access same data.
A user’s view is immune to changes made in other views.
Users should not need to know physical database storage details.
DBA should be able to change database storage structures without affecting the users’ views.
Internal structure of database should be unaffected by changes to physical aspects of storage.
DBA should be able to change conceptual structure of database without affecting all users.
Data Independence and the ANSI-SPARC Three-Level Architecture
External/Conceptual mapping = Logical data independence
Conceptual/Internal mapping = Physical data independence
Logical Data Independence
Refers to immunity of external schemas to changes in conceptual schema.
Conceptual schema changes (e.g. addition/removal of entities).
Should not require changes to external schema or rewrites of application programs.
Refers to immunity of conceptual schema to changes in the internal schema.
Internal schema changes (e.g. using different file organizations, storage structures/devices).
Should not require change to conceptual or external schemas.
Physical Data Independence
Refers to immunity of external schemas to changes in conceptual schema.
Conceptual schema changes (e.g. addition/removal of entities).
Should not require changes to external schema or rewrites of application programs.
Logical Data Independence
Database Languages
Data Definition Language (DDL)
Data Manipulation Language (DML)
Procedural DML
Non-Procedural DML
Fourth Generation Languages
Allows the DBA or user to describe and name entities, attributes, and relationships required for the application
plus any associated integrity and security constraints.
Data Definition Language (DDL)
Provides basic data manipulation operations on data held in the database.
Data Manipulation Language (DML)
allows user to tell system exactly how to manipulate data.
Procedural DML
allows user to state what data is needed rather than how it is to be retrieved.
Non-Procedural DML
Integrated collection of concepts for describing data, relationships between data, and constraints on the data in an organization.
Data Model
Data Model comprises:
a structural part;
a manipulative part;
possibly a set of integrity rules.
purpose of data model
To represent data in an understandable way.
Categories of data models include:
Object-based
Record-based
Physical.
Object-Based Data Models includes
Entity-Relationship
Semantic
Functional
Object-Oriented.
Record-Based Data Models includes
Relational Data Model
Network Data Model
Hierarchical Data Model.
_____ is the core of a system supporting all user views.
Conceptual schema
______ is process of developing a model of information use that is independent of implementation details.
Should be complete and accurate representation of an organization’s data requirements.
Conceptual modeling
____ is a conceptual data model.
Result
Functions of a DBMS
Data Storage, Retrieval, and Update.
A User-Accessible Catalog.
Transaction Support.
Concurrency Control Services.
Recovery Services.
Authorization Services.
Support for Data Communication.
Integrity Services.
Services to Promote Data Independence.
Utility Services.
