INTRODUCTION TO DATABASES- ANSI-SPARC Flashcards
What is ANSI-SPARC in full?
American National Standards Institute Standards Planning And Requirements Committee
Explain the first level: External view
This is the highest level of data abstraction.
It describes only part of the entire database that a end user concern.
It is also known as an view level.
End users need to access only part of the database rather than entire database.
Different user need different views of database. And so, there can be many view level abstractions of the same database.
*See diagram
Explain the second level: Conceptual view
This is the next higher level than internal level of data abstraction.
It describes What data are stored in the database and What relationships exist among those data.
It is also known as Logical level.
It hides low level complexities of physical storage.
Database administrator and designers work at this level to determine What data to keep in database.
Application developers also work on this level.
*See diagram
Explain the third level: Internal view
This is the lowest level of data abstraction.
It describes How the data are actually stored on storage devices.
It is also known as physical level.
It provides internal view of physical storage of data.
It deals with complex low level data structures ,file structures and access methods in detail.
It also deals with Data Compression and Encryption techniques, if used.
*See Diagram
What is a database schema?
An overall description of a database.
Can also be called the intension of the database
What are the types of schema?
External schema
Conceptual schema
Internal schema
*There is only one conceptual and internal schema per database but there may be more than one external schema
A DBMS is involved in mapping between the three schema. What does this involve?
- Confirming that each external schema is derivable from the conceptual schema
- Using the information in the conceptual schema to map between each external schema and the internal schema
What is conceptual-internal mapping and what is its purpose?
The conceptual schema is related to the internal schema by conceptual-internal mapping
It enables the DBMS to find the actual record or the combination of records in physical storage that constitutes a logical record in the conceptual schema.
Also enables the DBMS to find any constraints to be enforced on operations for the logical record
What external-conceptual mapping and what is its purpose?
Each external schema is related to the external schema by external-conceptual mapping
This enables the DBMS to map names in the user’s end view to the relevant part of the schema
What is a database instance?
Data in the database at any particular point in time.
Also called an extension (or state) of the database
What are the two kinds of data independence?
Logical- It should be possible to make changes to the conceptual schema without affecting the external schema or having tp rewrite application programs
Physical- It should be possible to make changes to the internal schema without affecting the external schema or the conceptual schema
Briefly explain four reasons why views are an important aspect for database management
systems
- Views can hide the complexity of the database and the data the user must hide that.
- Views can provide additional security from unauthorized users and unauthorized access.
- Views provide data independence to an application as the application depends on a view but not on a real table. Therefore, any change in the table will not affect the application, and an application will always be independent of the table schema design.
- Views can act as aggregated tables where aggregated data (sum, average, etc.) are calculated and presented as part of data.
- Views can join and simplify the tables in a virtual table.
- Views do not require additional storage.
Discuss the reasons for the three-level architecture (external, conceptual and internal) for a Database Management System
-Same data can be accessed by different users with different customized views.
-The user is not concerned about the physical data storage details. -Provides data abstraction.
-Physical storage structure can be changed without requiring changes in internal structure of the database as well as users view.
Conceptual structure of the database can be changed without affecting end users.
Security is improved since the client does not have direct access to the database; it is more difficult for a client to obtain unauthorized data.
Using examples, discuss the concepts of logical data independence and physical data
independence in ANSI-SPARC 3-level database architecture
Physical data independence helps you to separate conceptual levels from the internal/physical levels. It allows you to provide a logical description of the database without the need to specify physical structures. Eg Due to Physical independence, Using a new storage device like Hard Drive or Magnetic Tapes will not affect the conceptual layer.
Logical Data Independence is the ability to change the conceptual scheme without changing either External views or External API or programs. Eg Add/Modify/Delete a new attribute, entity or relationship is possible without a rewrite of existing application programs
which type of data independence is harder to achieve and why?
Logical data independence is more difficult to achieve than physical data independence, since application programs are heavily dependent on the logical structure of the data that they access.
