1. Chapter 2 CIS548.101 Sungchul Hong
Database Environment
Chapter 2
CIS
Sungchul Hong

2. The Three-Level ANSI-SPARC Architecture
External
Conceptual
Internal
<fig. 2.1>

3. Separation of Logical and Physical Presentation
Each user should be able to access the same data, but have a different customized view of the data.
Users should not have to deal directly with physical database storage details.
DBA should be able to change the database storage structures without affecting the users’ views.
The internal structure of the database should be unaffected by changes to the physical aspects of storage.
The DBA should be able to change the conceptual structure of the database without affecting all users.

4. External Level
Users’ view of the database. This level describes that part of the database that is relevant to each user.
External views
Different views may have different representations of the same data.

5. Conceptual Level
The community view of the database. This level describes what data is stored in the database and the relationships among the data.
Logical structure of entire database
All entities, their attributes, and their relationships
The constraints on the data
Semantic information about the data
Security and integrity information

6. Internal Level
The physical representation of the database on the computer. This level describes how the data is stored in the database.
Storage space allocation for data and indexes.
Record descriptions for storage.
Record placement
Data compression and data encryption techniques.

7. Schemas Database schema External schemas (subschema) Conceptual schema
Different views of the data
Conceptual schema
Describes all the entities, attributes,and relationships together with integrity constraints.
Internal schema
Complete description of the internal model, containing the definitions of stored records, the methods of representation, the data fields, and the indexes and hashing schemes used.

9. Mappings
The DBMS is responsible for mapping between these three types of schema.
Check consistency.
Conceptual/internal mapping
Find the actual record of a logical record
External/conceptual mapping
Map names in the user’s view on to the relevant part of the conceptual schema

11. Database Instance
Database schema is not expected to change frequently.
Database instance
The data in the database at any particular point in time.

12. Data Independence
Upper levels are unaffected by changes to lower level.
Logical data independence
Refers to the immunity of the external schemas to changes in the conceptual schema.
Physical data independence
Refers to the immunity of the conceptual schema to changes in the internal schema.

13. Data Definition Language
A language that allows the DBA or user to describe and name the entities, attributes,and relationships required for the application, together with any associated integrity and security constraints.
System catalog (meta data, data dictionary)

14. Data Definition Language (DDL)
The DDL us used to define a schema or to modify an existing one.
System catalog
Data dictionary

15. The Data Manipulation Language (DML)
A language that provides a set of operations to support the basic data manipulation operations on the data held in the database.
Insertion, modification, retrieval, deletion of data
Query language
Procedural DMLs
Non-procedural DML (SQL)

16. Fourth-Generation Languages (4GLs)
What v.s. How
Forms generator
Report generators
Graphics generators
Application generators

17. Data Models and Conceptual Modeling
An integrated collection of concepts for describing and manipulating data,relationships between data, and constraints on the data in a organization.
Structural part
Manipulation part
Set of integrity rules
Relational, network, hierarchical, Object-Oriented

18. Relational Data Model

19. Network Data Model

20. Hierarchical Data Model

21. Conceptual Modeling
The process of constructing a model of the information use in an enterprise that is independent of implementations details such as the target DBMS, application programs, programming languages, or any other physical considerations.

22. Functions of a DBMS Data storage, retrieval, and update
A user-accessible catalog (meta data)
Transaction support (update salary)
Concurrency control services
Recovery service
Authorization service
Support for data communication

23. Functions of a DBMS (2) Integrity services
Services to promote data independence
Utility service
Import, monitoring, statistical analysis, index reorganization, garbage collection.

24. Components of a DBMS Query processor Database manager File manager
DML preprocessor
DDL compiler
Catalog manager
Authorization control

25. Components of a DBMS (2) Command processor Integrity checker
Query optimizer
Transaction manager
Scheduler
Recovery manager
Buffer manager

28. Multi-User DBMS Architectures
Teleprocessing
File-Server
There is a large amount of network traffic
A full copy of the DBMS is required on each workstation.
Concurrency, recovery, and integrity control are more complex.
Client-Server

30. Client-Server It enables wider access to existing databases.
Increased performance.
Different types of computers works in parallel.
Hardware cost are reduced.
Communication costs are reduced.
Increased consistency – single server
It maps on to open-systems architecture naturally.