Comp 1314 Data Management 1 Flashcards
(108 cards)
1
Q
What are the three key features of an OS?
A
Multi-user: Many users same system at the same time
Multi-processing: Multiple processors at the same time
Multi-tasking: Multiple processes at the same time
2
Q
What is the philosophy of UNIX?
A
Set the cultural norms for minimalistic modular software development
3
Q
What is special about UNIX?
A
Programs can be stringed together but it is secure as programs do not know about each other
4
Q
What is Linux based on?
A
UNIX
5
Q
What is piping?
A
Redirecting the input and/or output of a program
6
Q
What is the symbol for piping?
A
|
Program1 | Program2
7
Q
What is the Input/Output redirection symbol?
A
<: Input
>: Output
»: Append
8
Q
List some programs that you can use
A
Head
Tail
sort
wc
uniq
du
xargs
more
cut
find
tar
gzip
nohup
parallel
basename
9
Q
What are the environmental variables?
A
A set of variables that every running process has access to
Set using the export command
10
Q
How do you write a for loop in bash?
A
for var in directionory;
do
something
done;
11
Q
How do you do a while loop in bash?
A
cat file | while read line;
do
something
done;
12
Q
What does grep do?
A
Searches for the input provided in the text provided
Can even use regular expressions
13
Q
What does SED stand for?
A
Text Stream Editor
14
Q
What does SED do?
A
Reads the input provided and modifies it as specified by the command and then writes that to the standard input
sed [options] command [file]
15
Q
What does scp do?
A
Securely copies files from a secured server
16
Q
What does awk do?
A
For processing structured text files into rows and columns
17
Q
What are wildcards for?
A
Allows multiple arguments for commands (accessing multiple files becomes easy) using regular expressions
18
Q
What are the three permission categories?
A
u: users
g: group
o: others
19
Q
How do you change the permissions of a file?
A
chmod u+=x
chmod g-w*
You can also specify a decimal number which will be converted into binary and then assigned where each bit is a 1
20
Q
Who can change the permissions of a file?
A
The owner of a file and the superuser
21
Q
What is everything in UNIX?
A
Either a file or a process, this include directories.
22
Q
How can you move a process to the background?
A
bg
Adding a & symbol will begin the process in the background
23
Q
What are the two options with the kill command?
A
SIGTERM: A gentle request to kill, giving the process time to close
SIGKILL: A hard-request with no clean up time.
23
Q
How can you prevent all processes terminating when you log off?
A
With screens
24
What is a CSV file?
Comma separate values
Easy to manipulate and process but new lines and commas in text can be problematic
25
What does YAML stand for?
Yet Another Markup Language
Fixed Row and column format
Widely used within config files and passing messages between applications
Made of key-value pairs
26
What does JSON stand for?
JavaScript Object Notation
27
What are the benefits of being understandable as a machine?
Searching
Aggregation and Summarisation
Prediction
28
What is metadata?
Data that is useful for the machine, but not for the human.
29
What is markup?
Contains a bunch of semantic links to other pages.
30
What is SGML?
Standard Generalised Markup Language
A superset of all markup language
Separate structure from content
31
What is XML?
Extensible Markup Language
Designed to carry data, not display data
32
What must XML have?
A root element
33
What is the issue with namespaces?
XML files can reference other XML files and people can define two tags with the same name
34
How is the namespace problem resolved?
Using the special namespace tag to separate the two documents apart.
35
What is a URI?
A unique full name of the namespaces, by convention this is used as the URL but they are not the same.
36
What does a schema enable us to do?
Gives meaning to the structured data we work with, lots of people have already done this.
So there are a lot of different schemas
37
Give an example schema
38
How can we specify the number of occurrences in a sequence?
minOccurs
maxOccurs
39
What does DTD stand for?
Document Type Definition
40
What is XSD?
XML Schema Definition
Every element is either simple or complex
41
How many parsers does HTML5 contain?
2
One which can parse HTML or XML
42
Why is XML not used for large scale solutions?
We could easily loose all of the data, database can mitigate this.
43
What is a DBMS?
Database Management System
A collection of software that manages a database
44
Why do we need DBMS?
Handles all the data exchange and creates data independence
Applications don't need to care about the database
45
What is logical and physical independence?
Logical: Protect from change in the data structure
Physical: Protect from changes in how the data is stored
46
What does the DBMS manage?
The data model
Store large amounts of data persistently, conveniently and efficiently
Transaction management
Concurrency control
Access Control
Resiliency
47
What is a data model?
A collection of mathematical concepts for describing data
Every model has a data language
48
What are the two parts of a data language?
A data definition language
A data manipulation language
49
What is XPATH?
The Data manipulation language for XML
50
What properties does a relation have?
Each row represents a k-tuple of R
The ordering of rows is immaterial
All rows are distinct
The order of attributes should not be significant
The significance of each column is conveyed by the name we give it.
51
What is a k-ary relation scheme?
A relation name and an ordered sequence of k attributes
52
What is an instance of a relation scheme?
A relation that conforms to the schema
Arities match
Data types of attributes match
53
What is a key?
A set of attributes where any two different tuples cannot have the same value
54
What is a superkey?
For every relation R, X is a set of attributes of R, X is a superkey of R, if X -> A, for every attribute A of R
The set of all attributes will always be a superkey
55
What is a candidate key?
X is a candidate key of R where X is a minimal superkey of R
Where X is a superkey and there is no superkey Y such that Y is a subset of X
56
Describe the steps of the closure algorithm
X+ = {Ai : F ⊧ X → Ai } is the closure of X with respect to F * F ⊧ X → Y if and only if Y ⊆X+
INPUT: R, attribute set U, F, X is a subset of U
OUTPUT: X+ = {Ai : F⊧X → Ai }
Repeat until: X_n+1 == X_n
R(ABCDEFG)
F = {AB -> CD, C -> EG, D->H}
0. X={A,C}
1. X_0={A,C} only path is to EG
2. X_1={A
57
Why is bad database design a problem?
It can lead to anomalies
58
What is a functional dependency?
When two tuples within a relation agree on the values of A1,...,An then they also agree on B
A --> B
So the right side cannot change where the left side is the same.
59
What is splitting/combining in Functional dependencies?
We can split bigger functional dependencies into smaller ones and vice versa.
60
What is normalisation for?
Avoiding anomalies
61
Give examples of anomalies
Redundancy
Update anomalies
Insert anomalies
Deletion anomalies
62
What is 1st Normal Form?
A relation that contains only atomic values with no repeating groups
63
What is 2nd Normal Form?
No partial key dependencies
Every non-key attributes is dependant on all attributes of all candidates keys
64
What is 3rd Normal Form?
All attributes are determined only by the keys
65
What is transitive dependence?
A -> B -> C but B does not determine A
66
What is Boyce-Codd Normal Form?
Every determinant is a candidate key
67
What are the benefits and drawbacks of BCNF?
Advantages:
No redundancy
Efficiency
No duplication
Changes can cascade across relations
Disadvantages:
More tables
More complex
More relationships
Queries become more complex
68
What is SQL?
Structured Query Language
Converts a data model to a physical databases by specifying a DDL and a DML
69
What is SQLite?
All of the database contained within a single file.
Simple databases
70
What types does SQL use?
INTEGER
REAL
TEXT
BLOB
NULL
71
What joins are possible in SQLite?
LEFT: All of 1 and matches in 2
RIGHT: All of 2 and matches in 1
FULL OUTER: Everything from both
72
What are views?
Virtual tables which have a name and can run queries. Pre-joined for convenience
73
What are indexes?
Data structures associated with tables to support queries, logically ordered by the values of the key.
74
Why are indexes used?
To improve the performance of looking up data
75
How is an index created?
CREATE INDEX ON
