Week 11 UAS Flashcards Preview

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Flashcards in Week 11 UAS Deck (15):

What is Distributed Database?

A logically interrelated collection of shared data (and a description of this data), physically distributed over a computer network.


What is Distributed DBMS?

Software system that permits the management of the distributed database and makes the distribution transparent to users.


What is Distributed processing?

A centralized database that can be accessed over a computer network


What is Parallel DBMS?

A DBMS running across multiple processors and disks that is designed to execute operations in parallel, whenever possible, in order to improve performance.

3 main architectures for parallel DBMS:
1. shared memory is a tightly coupled architecture in which multiple processors within a single system share system memory.
2. shared disk is a loosely couple architecture optimized for applications that are inherently centralized and require high availability and performance.
3. shared nothing is a multiple-processor architecture in which each processor is part of a complete system, with its own memory and disk storage.


Advantages of Distributed DBMS?

1. Reflects organizational structure
2. Improved shareability and autonomy
3. Improved availability
4. Improved reliability
5. Improved performance
6. Economics
7. Modular growth
8. Integration
9. Remaining competitive


Disadvantages of Distributed DBMS?

1. Complexity
2. Cost
3. Security
4. Integrity control more difficult Lack of standards
5. Lack of experience
6. Database design more complex


Types of DDBMS?

1. Homogeneous DDBMS
3. Heterogeneous DDBMS


What is Multidatabase system?

A distributed DBMS in which each site maintains complete autonomy


Functions of a DDBMS?

1. Extended communication services.
2. Extended Data Dictionary.
3. Distributed query processing.
4. Extended concurrency control.
5. Extended recovery services.


3 key factors in Distributed Database Design?

1. Fragmentation
Relation may be divided into a number of sub-relations, which are then distributed.
2. Allocation
Each fragment is stored at site with “optimal” distribution.
3. Replication
Copy of fragment may be maintained at several sites.


Why fragment?

1. Usage
Applications work with views rather than entire relations.
2. Efficiency
Data is stored close to where it is most frequently used. Data that is not needed by local applications is not stored.
3. Parallelism
With fragments as unit of distribution, transaction can be divided into several subqueries that operate on fragments.
4. Security
Data not required by local applications is not stored and so not available to unauthorized users.

1. Performance, may be slower
2. Integrity, because data and functional dependencies are fragmented and located at different sites.


3 correctness rules in Fragmentation?

1. Completeness,
2. Reconstruction,
3. Disjointness.


4 types of fragmentation?

1. Horizontal,
2. Vertical,
3. Mixed,
4. Derived.


4 main types of transparency in a DDBMS?

1. distribution transparency
a. Fragmentation Transparency
b. Location Transparency
c. Replication Transparency
d. Local Mapping Transparency
e. Naming Transparency
2. transaction transparency
a. Concurrency transparency
b. Failure transparency
3. performance transparency
4. DBMS transparency


Date's 12 Rules for a DDBMS?

1. Local Autonomy
2. No Reliance on a Central Site
3. Continuous Operation
4. Location Independence
5. Fragmentation Independence
6. Replication Independence
7. Distributed Query Processing
8. Distributed Transaction Processing
9. Hardware Independence
10. Operating System Independence
11. Network Independence
12. Database Independence

last four rules are ideals