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Database > Unit 2 > Flashcards

Unit 2 Flashcards

ahhh shiii here we go again (64 cards)

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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
Client server arc types
Two and three tier
26
Two tier client server
3 components of app are divided to client application code and database server client -presentation client & server - process Server - store
27
What are the three components of an application
Presentation, processing and data
28
disadvantage of the 2 tier client server arc
performance ↓ with ↑ users Users need to remember and manage different logins for each database
29
Three tier client server arc
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
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
Oui oui
31
Advantage of 3 tier client server arc
reduced cost due to apps running in web browser app logic centralized in an app server ↑ modularity LE meilleur arc
32
which tier is harder to maintain: two tier/ three tier
three tier
33
why is the three tier more secure?
Cause direct client to database communication is prevented
34
what is an entity
a real world concept
35
Attribute?
Descriptive characteristic of an entity
36
Record?
what's inside an attribute
37
Meta data is data about data but still metadata?
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
Where is meta data stored?
Data Dictionary or System Catalog
39
What is a data model
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
Data model types:
external, conceptual and internal
41
External Data Model
represent each user’s VIEWS of the organization aka the Universe of Discourse (UoD),
42
Conceptual Data Model
represent the conceptual (or community) view that is DBMS independent; what the system contains View of the user in the real world
43
Internal/logical Data Model
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
Which data model shows Show relationships among data including: * Constraints * Semantic information (e.g., business rules) * Security and integrity information
Conceptual
45
Other models of data
Object-based Record-based Physical
46
Physical data model
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
Physical data model is managed by
OS (storage and file management)
48
Object based data model
based on the concept of Entity (distinct object) where Entity Relationship - considers only the data aspect Object oriented- considers both data n behavior
49
Record Based
Based on fixed format records each record has a fixed number of fields each field is a fixed length
50
What is the ER model
design/blueprint of a database high level conceptual data model the algorithm basically Based on entity/ attribute/relationship
51
Object oriented model
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
What are classes
Grouping of all objects with the same properties and behaviors
53
what are pointers
adresses that facilitate objects access and relationships between objects
54
Vrai ou faux: Class constructors method created object instances
Vrai, each object has a unique object id
55
Advantages of conceptual and logical
supports complex data structs has java features like inheritance and encapsulation Reusable, real world modeling, flexible
56
Disadvatages of conceptual and logical models
no universally defined data model Lacks theoretical foundation Relatively limited Complex
57
Hierarchical DB model
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
Drawbacks of hierarchical
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
Advantages of hierarchical
data sharing simple secure efficient with 1:many relationships
60
Network data model
Made to solve the short-comings of hierarchical Child can be connected to multiple parents Allows many to many relationship
61
Disadvantage of Network Model
Complex Not all relations can be handled by assigning them in the form of owners and members.
62
Relational Data Model
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
What is a tuple/attribute
a row/column
64

Database (5 decks)

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