Examen 3. Presentacion 6 Flashcards

1
Q

Semantic Data Control Involves

A

View management
Security control
Integrity control

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2
Q

Semantic Data Control Objective

A

Ensure that authorized users perform correct operations on the
database, contributing to the maintenance of the database
integrity.

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3
Q

View – virtual relation

A

generated from base relation(s) by a query
not stored as base relations

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4
Q

CREATE VIEW SYSAN(ENO,ENAME)
AS SELECT ENO,ENAME
FROM EMP
WHERE TITLE= “Syst. Anal.”

A

View – virtual relation Example

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5
Q

ELECT ENAME, PNO, RESP
FROM SYSAN, ASG
WHERE SYSAN.ENO = ASG.ENO

A

Views can be manipulated as base relations

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6
Q

SELECT ENAME, PNO, RESP
FROM SYSAN, ASG
WHERE SYSAN.ENO = ASG.ENO

A

Queries expressed on views

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7
Q

SELECT ENAME,PNO,RESP
FROM EMP, ASG
WHERE EMP.ENO = ASG.ENO
AND TITLE = “Syst. Anal.”

A

Queries expressed on base relations

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8
Q

CREATE VIEW ESAME
AS SELECT *
FROM EMP E1, EMP E2
WHERE E1.TITLE = E2.TITLE
AND E1.ENO = USER

A

To restrict access

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9
Q

CREATE VIEW SYSAN(ENO,ENAME)
AS SELECT ENO,ENAME
FROM EMP
WHERE TITLE=”Syst. Anal.”

A

Updatable

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10
Q

CREATE VIEW EG(ENAME,RESP)
AS SELECT ENAME,RESP
FROM EMP, ASG
WHERE EMP.ENO=ASG.ENO

A

Non-updatable

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11
Q

View Management in Distributed DBMS

A

Views might be derived from fragments.
View definition storage should be treated as database
storage
Query modification results in a distributed query
View evaluations might be costly if base relations are
distributed

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12
Q

Materialized View

A

Stored as a database relation, possibly with indices

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13
Q

Deferred mode

A

DDBMS: No need to access remote, base relations
Data warehouse: to speed up OLAP

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14
Q

Materialized View updating

A

Resembles data replication but there are differences
View expressions typically more complex
Replication configurations more general

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14
Q

When to Refresh a View Modes

A

Immediate mode, Deferred mode

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14
Q

Deffered Mode times

A

Lazily: just before evaluating a query on the view
Periodically: every hour, every day, etc
Forcedly: after a number of predefined updates

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14
Q

Deferred mode

A

Through separate refresh transactions
Triggered at different times with different trade-offs

15
Q

Immediate mode

A

As part of the updating transaction, e.g. through 2PC
View always consistent with base data and fast queries
But increased transaction time to update base data

15
Q

How to Refresh a View

A

Full computing from base data
Incremental computing by applying only the changes to
the view

16
Q

Data Security

A

Data protection
Access control

17
Q

Data protection

A

Prevents the physical content of data to be understood by unauthorized users
Uses encryption/decryption techniques

18
Q

Access control

A

Only authorized users perform operations they are allowed to on database objects

19
Q

Types of access control

A

Discretionary access control (DAC)
Multilevel access control (MAC)

20
Q

DAC’sMain actors

A

Subjects (users, groups of users) who execute operations
Operations (in queries or application programs)
Objects, on which operations are performed

21
Q

Problem with DAC

A

A malicious user can access unauthorized data through
an authorized user

22
Q

Multilevel Access Control

A

Different security levels
Access controlled by 2 rules
A relation can be classified at different levels
A classified relation is thus multilevel

23
Q

Different security levels

A

Top Secret > Secret > Confidential > Unclassified

24
Q

No read up

A

subject S is allowed to read an object of level L only if level(S) ≥ L
Protect data from unauthorized disclosure, e.g. a subject with secret
clearance cannot read top secret data

25
Q

No write down

A

subject S is allowed to write an object of level L only if level(S) ≤ L
Protect data from unauthorized change, e.g. a subject with top secret
clearance can only write top secret data but not secret data (which could
then contain top secret data)

26
Q

A relation can be classified at different levels

A

Relation: all tuples have the same clearance
Tuple: every tuple has a clearance
Attribute: every attribute has a clearance

27
Q

Additional problems in a distributed environment

A

Remote user authentication
Management of DAC rules
Covert channels in MAC

28
Q

Semantic Integrity Control

A

Maintain database consistency by enforcing a set of
constraints defined on the database.

29
Q

Structural constraints

A

Basic semantic properties inherent to a data model e.g., unique key constraint in relational model

30
Q

Behavioral constraints

A

Regulate application behavior, e.g., dependencies in the
relational model

31
Q

Two components

A

Integrity constraint specification
Integrity constraint enforcement

32
Q

Predefined constraints

A

Not-null attribute, Unique key, Foreign key, Functional dependency

33
Q

Precompiled constraints Definition

A

Express preconditions that must be satisfied by all tuples in a relation for a given update type

34
Q

Precompiled constraints

A

Domain constraint, Domain constraint on deletion, Transition constraint

35
Q

General constraints Definition

A

Constraints that must always be true. Formulae of tuple
relational calculus where all variables are quantified

36
Q

General constraints

A

Functional dependency, Constraint with aggregate function,