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Database > Unit 2 > Flashcards

Unit 2 Flashcards

ahhh shiii here we go again

1
Q

What is an instance?

A

Collection of a data in a database at a particular moment

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2
Q

Schema

A

Overall design

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3
Q

Subschemas

A

Having several schemas at view level

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4
Q

Vrai ou faux: logical schema is by far the most important, in terms of its effect on application programs, since programmers construct applications by using
the logical schema

A

Vrai. I was about to say it was the physical one…welp

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5
Q

Vrai ou faux: the physical schema can be easily changed without affecting the application program.

A

Vrai. Since it is hidden beneath the logical schemas

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6
Q

ANSI-SPARC can be divided to:

A

Internal, conceptual and external

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7
Q

Internal level

A

AKA physical level

how data is stored in a storage

File structures and access methods

Data compression and encryption techniques

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8
Q

Conceptual

A

AKA logical(community view)

What is stored and what relationships exist

Abstracts low level complexities of the physical storage

The level app developers work on

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9
Q

External

A

AKA view level

What the end users use

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10
Q

What are the objectives of the 3TA(three tier arc)

A

DATA ABSTRACTION

views allow data to be viewed for d/t users

user doesn’t care about the physical storage detail

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11
Q

Vrai ou faux: Physical storage structure can be changed without requiring changes in
conceptual structure of the database as well as users view

A

Vrai

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12
Q

Vrai ou faux: Conceptual structure of the database can be changed without affecting end
users.

A

vrai encore

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13
Q

What is Data Independence

A

allows changes to be made to a database without affecting the applications that use it

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14
Q

Logical data independence:

A

conceptual doesn’t change the external schema and vise versa

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15
Q

Physical data independence

A

conceptual doesn’t change the internal schema and vise versa

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16
Q

Layers of ANSI-SPARC organ data

A

external and Internal

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17
Q

External Mapping

A

the DBMS maps names in the user’s view to the relevant part of the conceptual schema (translator)

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18
Q

Internal Mapping

A

(Navigator) DBMS funds the records in physical storage based on the constraints…ig

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19
Q

Multi- User architectures

A

Tele processing, file and client server

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20
Q

Main-Frame (teleprocessing)

A

Mainframe dependent, uses dumb terminals to access apps and the database

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21
Q

File Server

A

One computer(file server) connects to workstations and they share storage, the apps run on the workstation while asking the file server files when necessary

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22
Q

disadvantages of file server

A

Heavy network traffic

Cost of ownership

Complex integrity, concurrency, and recovery control

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23
Q

Client Server arc

A

The client and server
don’t reside on the same machine

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24
Q

What is a server?

A

device that provides and manages, access to a
centralized resource or service to another device , program or end user in a network

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25
Q

Client server arc types

A

Two and three tier

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26
Q

Two tier client server

A

3 components of app are divided to client application code and database server

client -presentation
client & server - process
Server - store

27
Q

What are the three components of an application

A

Presentation, processing and data

28
Q

disadvantage of the 2 tier client server arc

A

performance ↓ with ↑ users

Users need to remember and manage different logins for each database

29
Q

Three tier client server arc

A

components of application are separated

Presentation layer- UI and communication

Application/logic/middle - business and data processing logic and can add, delete, or modify data in the data tier

Data tier- data validation, manage DB access

30
Q

Vrai ou faux: In a three-tier application, all communication goes through the application tier. The
presentation tier and the data tier cannot communicate directly with one another

A

Oui oui

31
Q

Advantage of 3 tier client server arc

A

reduced cost due to apps running in web browser

app logic centralized in an app server

↑ modularity

LE meilleur arc

32
Q

which tier is harder to maintain: two tier/ three tier

A

three tier

33
Q

why is the three tier more secure?

A

Cause direct client to database communication is prevented

34
Q

what is an entity

A

a real world concept

35
Q

Attribute?

A

Descriptive characteristic of an entity

36
Q

Record?

A

what’s inside an attribute

37
Q

Meta data is data about data but still metadata?

A

Describes length and composition ( basically based on the datatype

Stores structure, definition,
purpose, storage, number of columns and records, dependencies, access rights, owner… of an object

38
Q

Where is meta data stored?

A

Data Dictionary or System Catalog

39
Q

What is a data model

A

collection of conceptual tools for describing data, data relationships, data
semantics, and consistency constraints

shows how data is manipulated

has structural part, manipulative part and possibly a set of integrity rules

40
Q

Data model types:

A

external, conceptual and internal

41
Q

External Data Model

A

represent each user’s VIEWS of the organization aka the Universe of Discourse (UoD),

42
Q

Conceptual Data Model

A

represent the conceptual (or community) view
that is DBMS independent;
what the system contains

View of the user in the real world

43
Q

Internal/logical Data Model

A

represent the logical schema in such a way that it
can be understood by the DBMS

Designed and developed independently from the DBMS.

View in the database

44
Q

Which data model shows Show relationships among data including:
* Constraints
* Semantic information (e.g., business rules)
* Security and integrity information

A

Conceptual

45
Q

Other models of data

A

Object-based
Record-based
Physical

46
Q

Physical data model

A

HOW it is implemented

physical representation ☺

Describes how the data is stored and deal with…Run-time performance, Storage utilization and compression, File organization and access methods and Data encryption

47
Q

Physical data model is managed by

A

OS (storage and file management)

48
Q

Object based data model

A

based on the concept of Entity (distinct object) where
Entity Relationship - considers only the data aspect

Object oriented- considers both data n behavior

49
Q

Record Based

A

Based on fixed format records

each record has a fixed number of fields

each field is a fixed length

50
Q

What is the ER model

A

design/blueprint of a database
high level conceptual data model
the algorithm basically

Based on entity/ attribute/relationship

51
Q

Object oriented model

A

data is formed in the form of objects which have state and behavior

State-attribute
Behavior- methods/procedures

The designer defines classes with attributes/methods and relationships

52
Q

What are classes

A

Grouping of all objects with the same properties and behaviors

53
Q

what are pointers

A

adresses that facilitate objects access and relationships between objects

54
Q

Vrai ou faux: Class constructors method created object instances

A

Vrai, each object has a unique object id

55
Q

Advantages of conceptual and logical

A

supports complex data structs
has java features like inheritance and encapsulation
Reusable, real world modeling, flexible

56
Q

Disadvatages of conceptual and logical models

A

no universally defined data model

Lacks theoretical foundation

Relatively limited

Complex

57
Q

Hierarchical DB model

A

upside down tree?

other than the root, each record has one parent and many children

a parent node can have >1 child
one child can only have 1 parent

Relationship is established by creating physical link between records

Consists of boxes

58
Q

Drawbacks of hierarchical

A

can only have one to many relationship models

to add new records the DB must be refined and stored in a new form

hard to accomodate changes

Complex implementation

Requires physical data storage characteristics

59
Q

Advantages of hierarchical

A

data sharing
simple
secure
efficient with 1:many relationships

60
Q

Network data model

A

Made to solve the short-comings of hierarchical

Child can be connected to multiple parents

Allows many to many relationship

61
Q

Disadvantage of Network Model

A

Complex

Not all relations can be handled by assigning them in the form of owners and members.

62
Q

Relational Data Model

A

Uses a collection of tables to represent both data and the
relationships among those data

Can define more flexible and complex

Stores information in the form of tables

63
Q

What is a tuple/attribute

A

a row/column

64
Q
A

Database (5 decks)

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