Chapter 2 : Data Base Architecture Flashcards
What are the levels of DBMS architecture?
- External Level
- Conceptual Level
- Internal Level
- Physical Storage
What is the External View ?
The external view is concerned with the end user n highest level of abstraction , no DBMS knowledge is needed .
The database shows the user its part that the user needs and hides the rest.
What is Conceptual View?
The main purpose is to hide the physical data of the database and constrate on data relationship ,describing entities …
It ensures Overall query optimization , management of user conflicts
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What is Internal View ?
The Internal view is the view that tells us how the data is stored and how .
The following aspects are at this level : Storage information , access paths
What is Data indpendence and what are its types?
Data independence is the seperation between levels
The two types are Logical and Physical.
What Is Logical Independence?
If there’s a change in the conceptual level without affecting the physical or internal level
Example : the name field in the conceptual view is stored as First , Middle and Last name but in the external level it remains as a single name
What is Physical Independence?
If there’s a change in the internal level without affecting the conceptual level or external.
Example: If we change the database’s location from C drive to D , the external and conceptual level won’t be affected .
What are the responsibilities of a DBA?
- Ensuring the relationship between users
- Safety
- Intergity
- Migration and updates
- Perfomance
- Development aid and tests
- Recovery of Data and disaster management
What are the elements of a Database Connexion ?
- Start a tool that creates a User Process
- Connect To Oracle Server
- The connexion request will create Server Process
What is the User Process?
It runs on the Client Machine
It starts when the tool starts and ends when the user quits or forced to interrupt
It includes User Program Interface
What is the Server Process and Its types?
The server process loads disk data in memory for the user to handle .
It has two types : Dedicated Server and Shared Server .
What is the Dedicated Server Process?
Everytime a user initiates a session, a dedicated server is created just for that user
What is the Shared User Process?
User’s requests are routed to one or more Dispatchers it assigns the user’s request in a queue and the shared process executes them one by one.
How to alter between Shared Server or Dedicated Server?
change SHARED_SERVERS =0;
What are the elements of Database Server Architecture?
- Memory
- Process
- Storage
