1. The ANSI/SPARC Architecture of a Database Environment
Lecture 2

2. Schema and instance database schema database instance
the description of the database is called the database schema or intension;
specified at the creation of the database
not expected to change very often
database instance
the raw data that populates a database at a particular moment in time is called a database instance of the extension of the database

3. Schema and instance - example

4. Levels of access to data

5. The three ANSI/SPARC levels of abstraction

6. Schemas and mappings schemas mappings
external
conceptual
internal
mappings
external / conceptual
conceptual / internal
data catalogue/dictionary  schemas  mappings

7. External / conceptual example

8. Conceptual / internal - example

9. Program - data independence
physical
the immunity of application programs to changes at the internal level
logical
the immunity of application programs to changes at the conceptual level

10. The components of a database environment

11. Data types characteristics primary derived integrated shared extensive
data = raw data + data dictionary

12. Hardware storage space computational power permanent / secondary
temporary / primary
computational power

13. Software

14. Application programs user developed provided by developers
in a third generation language
provide an embedded data sub-language
provided by developers
fourth generation language
examples: query processors, statistical packages, reports/forms generators

15. Database management system
provides support for
data manipulation / definition
data sub-languages (computationally incomplete)
data integrity
security control
recovery services
concurrency facilities
data communication
accessing the data dictionary
why needed? applications’ automatic access to the DB

16. People data administrator database administrator
relevance and meaning of data; standards; policy
database administrator
design, implementation and maintenance of the DB
application programmers
end user

17. Summary
the three level ANSI/SPARC architecture of a database environment
the components of a database environment

18. Activity A2
Which role within a database environment would you prefer to be in, if you were able to choose? Why? Which activities would you be interested in performing? How would you like to co-operate with the people performing the other roles?