What is metadata?
System catalog / data dictionary
What are the 4 types of Databases?
- Single user: Supports only one user at a time.
- Multi-user: Supports multiple users at the same time.
- Centralized: Supports data being located at a single site.
- Distributed: Supports data being distributed across several sites.
What are the 5 components of DBMS Environment?
- Hardware
- Software
- Data
- Procedures
- People
Name 4 Components of a Database.
- Meta-data repository (data dictionary)
- Data repository (Actual storage facility)
- Database interface (link between the data contained in the database and the external world)
- CASE tools
Name some advantages of Integrated DBMS.
- Better control of data redundancy
- Improved data consistency
- Improved data security
- Increased productivity
Name some disadvantages of DBMS.
- High cost
- Size of DBMS
- Complexity
Name 5 People’s Roles in the Database Environment.
- Data Administrators (DA)
- Database Administrators (DBA)
- Database Designers (Logical & physical)
- Application programmers
- End users
What is the concept of ‘Views’ with a DBMS?
- Allow each user to have his or her own view of the database.
- Security: Allow viewing of data without permission to change contents of a database.
- The user can only see parts of the data contained in the database.
Name some benefits of ‘Views’.
- Provide a level of security.
- Provide a mechanism to customize the appearance of the database.
- Present a consistent, unchanging picture of the structure of the database, even if the underlying database is changed.
What does the ANSI-SPARC, 3 Level Architecture provide?
This conceptual architecture:
- Provides a basis of understanding some of the functionality of a DBMS
- Emphasizes the implementation-independent layers needed to separate application programs from the data
What are the 3 levels of ANSI-SPARC Architecture?
- External Level
- Conceptual Level
- Internal Level
What is the External Level of ANSI-SPARC Architecture?
The way users perceive the data in the External level.
What is the Conceptual Level of ANSI-SPARC Architecture?
The conceptual level provides the mapping details, and aids the separation/independence between other two levels. (Logical structure of entire database)
What is the Internal level of ANSI-SPARC Architecture?
The way the operating system and DBMS perceive the data is the Internal level. (How data is organized)
Name 3 objectives of ‘Users’.
- All users should be able to access the same data.
- A user’s view is immune to changes made in other views.
- Users should not need to know the physical database storage details.
Name 3 objectives of ‘Database Administrators’ (DBA).
- DBA should be able to change the database storage structure without affecting the users’ views.
- Internal structure of a database should be unaffected by the changes to the physical aspects of storage.
- DBA should be able to change the conceptual structure of a database without affecting all users.
What is a ‘Schema’?
A schema is means of defining a view: An external schema defines an external view, the conceptual schema defines the conceptual view etc…
What are 3 types of Schemas?
- Internal schemas (Describes the data storage structures and the access paths)
- Conceptual schemas (Describes the structure and constraints for the whole database: Entities, attributes, relationships etc…)
- External schemas (Describe the various user views)
What does Logical Data Independence refer to?
Refers to the immunity of external schemas to changes in the conceptual schema.
What does Physical Data Independence refer to?
Refers to the immunity of conceptual schema to changes in the internal schema.
Name some functions of a DBMS.
- Data storing
- Retrieval
- Update
What is a System Catalog?
A system catalog is a repository of information (metadata) describing the data in the database.
What does a system catalog typically store?
- Names, types and sizes of data items.
- constraints on the data.
- Names of authorized data.
- Usage statistics.
