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Distributed DB > chapter 1 > Flashcards

chapter 1 Flashcards

1
Q

What is a Distributed Database System (DDBS)?

A
  • Is the union of database system and computer network technologies.
  • This addresses the limitations of traditional database systems, which are characterized by a centralized approach to data processing.
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2
Q

Distributed database system (DDBS) shifted the Database paradigm from ____ to ______ ?

A

■ from data processing in which each application defined and maintained its own data

■ to one in which the data are defined and administered in a central repository

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3
Q

What is Data Independence?

A
  • Refers to the concept that application programs are immune to changes in the logical or physical organization of the data, and vice versa.
  • This means that changes to how data is structured (logical) or stored (physical) do not impact the application programs, and changes to applications do not affect how data is managed.
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4
Q

What is the Initial motivation behind the use of database systems?

A

■ The desire to integrate the operational data of an enterprise
■ To provide centralized and controlled access to that data

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5
Q

Given the contrasting nature of centralization efforts in database technology and the decentralized nature promoted by computer networks, how are these 2 approaches used together?

A

Integration vs. Centralization

Objective: The main goal of database technology is integration rather than centralization. This implies that the focus is on bringing together diverse data sources and making them accessible in a cohesive manner.

Realization: The understanding here is that integration doesn’t necessarily require centralization. It is possible to achieve a unified view of data without concentrating all data management in a single location.

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6
Q

What is a Distributed computing system?

A
  • Refers to autonomous processing devices that are interconnected by a computer network and that cooperate in performing tasks.
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7
Q

What elements can be distributed?

A
  1. Distribution of Processing Logic
  2. Distribution of Computer Functions
  3. Distribution of Data
  4. Distribution of Control
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8
Q

What are the motivation factors behind distribution?

A

▪ The organizational structure of today’s widely distributed enterprises,
▪ More reliable and more responsive
▪ many of the current applications of computer
technology are inherently distributed
▪ Local units want control over data.
▪ Reduce telecommunication costs.
▪ Reduce the risk of telecommunication failures

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9
Q

What is a Distributed Database?

A
  • Is a collection of multiple, logically interrelated databases distributed over a computer network.
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10
Q

What is a Distributed Database Management System (Distributed DBMS)?

A
  • Is the software system that permits the management of the distributed database and makes the distribution transparent to the users.
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11
Q

What are the three orthogonal dimensions of data delivery?

A

􏰀 delivery modes
􏰀 frequency
􏰀 communication methods.

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12
Q

What are Delivery Modes?

A
  • Refer to the ways in which data can be delivered from they are stored to where they are queried.
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13
Q

What are The three delivery modes?

A
  • pull-only
  • push-only
  • hybrid
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14
Q

Explain the Pull-Only Data Delivery Mode.

A
  • Initiation: Data transfer is initiated by a client pull.
  • Process: When a client request is received at a server, the server responds by locating the requested information.
  • Challenge: Servers must be continuously interrupted to handle client requests, and the information clients can obtain is limited to what they know to ask for explicitly.
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15
Q

Explain the Push-Only Data Delivery Mode.

A
  • Initiation: Data transfer is initiated by a server push in the absence of specific client requests.
  • Difficulty: Determining which data is of common interest and when to send them to clients is a challenge.
  • Alternatives: Periodic, irregular, or conditional approaches are used to decide when to push data.
  • Server Accuracy: The usefulness of server push depends heavily on the accuracy of the server in predicting the needs of clients.
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16
Q

Explain the Server Information Dissemination Methods used by Push-based modes?

A
  1. Random Broadcast
    ■ an unbounded set of clients who can listen to a
    medium
  2. Multicast
    ■ to selective set of clients who belong to some
    categories of recipients that may receive the data.
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17
Q

Explain the hybrid delivery mode.

A
  • Combines both client-pull and server-push mechanisms.
  • Benefits: This approach combines the advantages of both pull and push, allowing for proactive updates and reactive data retrieval.
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18
Q

What is Continuous Query Approach? explain in detail.

A

-Is a way of combining pull and push modes through continuous (or continual) query approach.

  • Example: Data transfer is initiated by a client pull (posing a query), and subsequent transfers of updated information to clients are initiated by a server push.
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19
Q

What are the Frequencies of data delivery?

A
  1. Periodic Delivery
  2. Conditional Delivery
  3. Ad hoc Delivery
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20
Q

In ________ are data are sent from the server to clients at regular intervals?

A
  1. Periodic Delivery
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21
Q

Give examples for Periodic Delivery [ push and pull ]?

A

■ Periodic pull
A client request for IBM’s stock price every week

■ Periodic push
an application sends out stock price listing on a
regular basis, say every morning.

22
Q

In _______ delivery, data are sent from servers whenever certain conditions are satisfied?

A

Conditional Delivery

23
Q

Give examples for Conditional Delivery.

A

■ An application that sends out stock prices only when they change
■ An application that sends out a balance statement only when the total balance is 5% below the pre-defined balance threshold.

24
Q

________ delivery is irregular and is performed mostly in a pure pull-based system?

A

Ad-hoc

25
Q

What are the Four fundamentals promises of DDBS technology?

A

■ Transparency
■ Reliability
■ Performance
■ Scaling

26
Q

What is Transparency?

A

■ refers to separation of the higher-level semantics of a system from lower-level implementation issues.

27
Q

A transparent system “hides” the implementation details from users.

A

True

28
Q

transparent access allows users can still pose queries [ SELECT ENAME AMT
FROM EMP, ASG, SAL ]
without paying any attention fragmentation, location, or replication of data.

A

True

29
Q

_______ refers to the fact that the command used to perform a task is independent of both the location of the data and the system on which an operation is carried out?

A

Location transparency

30
Q

______ means that a unique name is provided for each object in the database?

A

Naming transparency

31
Q

In the absence of Naming transparency users are required to embed ________ as an identifier?

A

the location name

32
Q

What is The Replication transparency issue is?

A

■ whether the users should be aware of the existence of copies or whether the system should handle the management of copies , the user should act as if there is a single copy of the data

33
Q

From a user’s perspective, it is preferable to be involved with handling of replicated data?

A

False

34
Q

_________ refers only to the existence of replicas, not to their actual location

A

replication transparency

35
Q

Explain Network transparency.

A
  • Distributing replicas across the network in a transparent manner
36
Q

Explain Fragmentation Transparency.

A

to divide each database relation into smaller fragments and treat each fragment as a separate database object.

Example: employees, projects and other related data.

■ EMP(ENO, ENAME, TITLE) and
■ PROJ(PNO,PNAME, BUDGET)
■ SAL(TITLE, AMT) to store salary information:
■ ASG(ENO, PNO, RESP, DUR) to store which projects employees have been assigned to

37
Q

Fragmentation helps with performance, availability, and reliability.

A

True

38
Q

______ can reduce the negative effects of replication.

A

fragmentation
- Each replica is not the full relation but only a subset of it [ thus less space is required ]

39
Q

List and describe the Two general types of fragmentation

A
  1. Horizontal fragmentation
    ■ a relation is partitioned sub-relations based on tuples (rows) of the original relation.
  2. Vertical fragmentation
    ■ a relation is partitioned sub-relations based on attributes (columns) of the original relation.
40
Q

handling user queries becomes a challenge when queries are specified on entire relations but need to be executed on sub-relations.

A

True

41
Q

The fundamental issue of dealing with fragmentation
transparency is ________ ?

A

query processing

42
Q

What is required during query processing in Fragmentation Transparency?

A

a translation from what is called a global query to several fragment queries.

43
Q

replicated components improve reliability by … ?

A

eliminating single points of failure

44
Q

What is Transaction?

A

▪ is a unit of reliable computing, having a sequence of database operations executed as an atomic action

45
Q

_______ transforms a consistent database state to another consistent database state

A

Transaction

46
Q

Give a A transaction Example?

A

bank atm thing

47
Q

What should be done To encapsulate a query within transactional boundaries?

A

declare the begin of the transaction and its end

48
Q

a distributed DBMS fragments the conceptual database, enabling data to be … ?

A

stored in close proximity to its points of use (also called data localization)

49
Q

What are the two potential advantages of data localization?

A
  1. competition for CPU and I/O services is not as severe as for centralized databases.
  2. reduces remote access delays
50
Q

Benefits of reduced contention / competition and reduced communication overhead can be obtained only by a proper ______ and _______ ?

A

􏰀 fragmentation and
􏰀 distribution of the database

Distributed DB (3 decks)

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